Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/09243046.2024.2396576

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

In this study, we proposed an electromagnetic induction testing method for measuring the electrical properties of carbon fiber reinforced thermoplastics (CFRTPs) along the through-thickness direction. The effectiveness of the transmission method, wherein the coil is placed opposite to the object to be measured, was demonstrated through finite element analysis and experimental measurements. The simulation results indicated that the output voltage of an interlaminar non-electrically conductive specimen exceeded that of an interlaminar conductive specimen due to the electromagnetic shielding effect. In the experiments, the impedance along the through-thickness direction depended on the lamination configuration and the presence of the PA-6 layer. Our findings indicate that the proposed method can be used to measure the changes in the electrical properties of CFRTP along the through-thickness direction.

DOI： 10.1016/j.ndteint.2024.103202

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Because moisture absorption changes the permittivities and electrical conductivities of carbon fiber reinforced plastics (CFRPs) with resin layers, electromagnetic induction testing (EIT) was used for evaluating CFRP moisture absorption. Conductivity and permittivity changes were obtained using a finite element analysis (FEA). A moisture-absorption test was conducted to deduce the relationship between the conductivity and moisture-absorption rate. The conductivity corresponding to CFRP moisture absorption was calculated and used in the FEA, while the permittivity corresponding to CFRP moisture absorption was numerically calculated. The simulation suggested that, as CFRPs absorbed moisture, the influence of displacement currents dominated in the EIT output. Finally, CFRP moisture absorption was analyzed using EIT. The results indicated that the EIT output tended to increase with moisture absorption, indicating the dominance of the displacement-current change due to resin moisture absorption in the moisture absorption. These results demonstrate the effectiveness of EIT for evaluating CFRP moisture absorption.

DOI： 10.1016/j.compositesa.2023.107934

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

EIT was found recently that it can also be applied to dielectrics under a high-frequency AC voltage. However, the EIT evaluation method for dielectrics has not been established sufficiently; in particular, there are no example studies of the drawing of impedance plane diagrams, which is widely used as an evaluation method for eddy current testing (ECT). Therefore, we have attempted to draw an impedance plane diagram based on the Ampère-Maxwell equation and a simple electrical circuit, as performed in ECT. First, a theoretical solution for the impedance based on the Ampère-Maxwell equation that considers eddy and displacement currents was derived, and impedance plane diagrams were then drawn. From the impedance plane diagrams obtained, it was shown that the same trends can be drawn for the diagrams for both conductors and dielectrics. Next, an electrical circuit model for EIT was proposed that takes into account both the conductivity and the permittivity. Using this model, impedance plane diagrams for conductors and dielectrics were drawn, and for dielectrics in particular, it was shown that the diagrams can be drawn by considering the conductivity. In addition, similar to the impedance plane diagrams drawn from the electrical circuit model and derived from the Ampère-Maxwell equation, the change behavior in the diagrams clearly differs between the cases where the conductivity and permittivity change and the case where the lift-off changes. This demonstrates the effectiveness of the electrical circuit model in providing a qualitative understanding of the effects of the dielectric conditions and measurement conditions on EIT.

DOI： 10.1007/s10921-024-01045-0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

In this study, we evaluated the effects of the fiber orientation and the presence of resin-rich layers on electromagnetic induction testing (EIT) of carbon fiber reinforced thermoplastics (CFRTPs). First, a finite-element analysis was performed to evaluate the distribution and path of the eddy and displacement currents induced in interlaminar conductive and interlaminar non-conductive CFRTP specimens. Second, interlaminar electrically conductive and interlaminar non-electrically conductive specimens of unidirectional CFRTP and cross-ply laminated CFRTP were fabricated using a 3D printer, with control of the number of PA-6 layers and fiber orientation. EIT of the specimens revealed that the presence of resin-rich layers and fiber orientation affected the measured EIT output. The results also indicated that the EIT of CFRTP with resin-rich layers requires penetration of displacement currents between the layers.

DOI： 10.1080/09243046.2023.2293603

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, an optimization method was developed to mini-mize the thickness of the cylindrical part of a carbon fiber reinforced plastic (CFRP)-composite overwrapped pressure vessel (COPV). This study extends the stress calculation equation of a pressure vessel with two layers subjected to internal pressure to multiple layers. This approach allowed the approximation of stress in each layer of the COPV with arbitrary stacking sequences and numbers of layers, reducing the computational costs. In this calculation method, only the strength of the cylindrical part of the COPV was considered. The stacking sequence was optimized to minimize the vessel thickness and maximum stress in the fiber direction under the condition that the inner diameter and thickness of a CFRP layer were constant. The optimization results show that the proposed method is reasonable because the stacking sequence is thinner than the existing tank stacking sequence. This omits the low-angle helical layer necessary to fabricate the dome part. Using the proposed method, we determined the possibility of optimizing the stacking sequence under arbitrary limiting conditions at a low computational cost. This study enables adding the allowable pressure for each damage mode (matrix cracking and fiber failure) to the limiting conditions or method optimization considering the strength development rate of fiber.

DOI： 10.11181/hpi.62.4

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

An approach was proposed to design high-pressure composite hydrogen vessels for fuel cell vehicles with damage tolerance. In addition, a stacking-sequence optimization method was developed, which was built upon the damage tolerance design. A no-growth approach, damage categorization, and residual strength requirements were proposed for the damage-tolerance design method for high-pressure hydrogen vessels, which were implemented in the damage-tolerance design method for composite aircrafts. The initial burst pressure was set at 180% of normal working pressure (NWP) assuming that the structural health monitoring (SHM) system with acoustic emission (AE) testing would immediately detect the occurrence of fiber failure. Stacking-sequence optimization was then conducted to minimize vessel thickness and meet the residual strength requirements. As a result of the optimization, the calculations confirmed that the vessel thickness could be reduced by approximately 52% of the existing vessel stacking sequence. The results show that the thickness of the vessel can be reduced by introducing a damage-tolerant design. Moreover, the proposed method for an optimal design based on the damage-tolerance design method is effective.

DOI： 10.1080/09243046.2024.2313312

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/09243046.2022.2095245

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/09243046.2022.2080989

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.compstruct.2023.117467

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Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, a convex micro-structure, single protrusion with a square profile, formed on adherend surfaces of single-lap adhesively-bonded joints as a crack propagation suppressor, and the performance of the convex structure was experimentally investigated by applying cyclic loads. Moreover, the change in crack propagation rate due to convex micro-structure was analytically discussed, focusing on strain energy release rate and stress field in the adhesive layer and the adherend. The experimental and analytical results revealed the crack propagation rate with convexity was lower than that without convexity around the convex micro-structure. In addition, the change ratio of crack propagation rate due to convex micro-structure did not depend on the test load levels. The reasons for suppressing crack propagation were considered the energy in the vicinity of the crack tip decreased due to the stress concentration around the convex microstructure and the limited displacement of the fractured adhesive interfered with the convex structure.

DOI： 10.11395/jjsem.23.236

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/00218464.2022.2088282

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jcomc.2022.100260

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/09243046.2022.2035303

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/00405000.2021.1957275

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/09243046.2021.1882163

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s12221-021-0423-1

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/00405000.2020.1742274

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/09243046.2019.1650323

Scopus

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compstruct.2019.111714

Web of Science

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society for Composite Materials  

<p>Continuous carbon fiber composites can be printed with 3D printers. Many studies detailing elucidations of the mechanical properties of such 3D printed composites have been published, all of which employed a conventional tensile specimen configuration with surface resin layers. In the present study, 0º, 90º, ±45º, and lay-up direction type specimens were newly designed for 3D printed composites without surface layers. Using the 3D printer, both conventional and newly designed specimens with serpentine folded fiber bundles were fabricated and investigated experimentally. The lay-up direction specimen was fabricated using 800 layers. The specimens without the serpentine folded fiber bundles were experimentally shown to be adequate for tensile tests. The lay-up direction specimen had the lowest strength and stiffness, which seems to be related to its surface roughness.</p>

DOI： 10.6089/jscm.45.141

CiNii Books

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publisher：The Japan Society for Composite Materials  

<p>Three-dimensional (3D) printing is a promising technology that can produce complex structures without the requirements of expensive tools and molds. Additives are usually incorporated into the plastic materials used in 3D printing to increase their strength and rigidity. Particularly, carbon fiber-reinforced plastic (CFRP) has shown great promise as a 3D printing material. However, the strength of CFRP after printing remains unknown, although it is well-known that its strength is affected by plastic melting during printing. Herein, we analyzed the fracture behavior of CFRP specimens before and after bending to different curvature radii. From the experimental results, a fracture criterion describing the material behavior by considering the tensile and compressive loads was developed. The fracture mechanism remained the same for CFRP specimens with different curvature radii. This study deepened our understanding of the mechanical properties of CFRP materials used in 3D printing.</p>

DOI： 10.6089/jscm.45.164

CiNii Books

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/09243046.2018.1558327

Scopus

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compstruct.2018.03.089

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

DOI： 10.1109/JSEN.2017.2773558

Scopus

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/transjsme.16-00359

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/09243046.2016.1239354

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4236/jtst.2017.31001

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/09243046.2016.1239354

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4236/ojcm.2017.73007

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/09243046.2015.1052132

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOCIETY FOR COMPOSITE MATERIALS  

Carbon fiber reinforced plastics (CFRPs) are generally used for weight reduction of industrial structures. Highly strong reinforced plastics and highly rigid matrixes in CFRP consist CFRP&prime;s high performance (e.g. specific strength and rigidity), while CFRP can be defected inside (e.g. deferent material interface or interlaminar) by off-plate directional impact load easily to reduce their strength significantly. Therefore, periodical non-destructive testing (NDT) is required for maintenance of their integrity. In addition, CFRP has remarkable mechanical and electrical anisotropy; especially electrical resistances are approximately 1000 times different between longitudinal and orthogonal direction. In this study, we propose new thermography method for CFRP delamination detection with electrical resistance heating of intentionally selected layer by using above-mentioned CFRP&prime;s electrical resistance anisotropy (selective-layer heating). This method can detect the delamination crack induced in an objective more deeply than the other thermography method that excite heat from an objective surface and can determine the delamination depth more precisely by excluding influence of 3-dimensional heat conduction than the other thermography method.

DOI： 10.6089/jscm.42.185

CiNii Books

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/09243046.2015.1087176

Web of Science

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.6089/jscm.42.98

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesa.2015.11.040

J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesb.2015.09.041

J-GLOBAL

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>Carbon fiber reinforced polymers (CFRPs) have high specific strength and many other advantages in mechanical properties compared with conventional metal materials. However, a small out-of-plane impact load can easily cause serious damage in a CFRP laminate because of its laminated structure composed of anisotropic layers. Although ultrasonic inspection is generally performed to detect the damage and estimate its location and size, the method usually requires both long inspection time and a large cost. Thus, a low-cost and in-situ system for monitoring collisions of foreign matters is required to identify the area where the ultrasonic inspection must be conducted. When a foreign matter, which is regarded as a charged body because any object is charged to a greater or lesser extent, approaches and hits grounded electric conductive materials such as a CFRP laminate, an electric current caused by electrostatic induction flows into the ground. We analyzed the electric current and conducted a falling-weight impact test to elucidate the mechanism of generation of the electric current. In addition, we proposed a collision monitoring system which utilizes the characteristic waveform of the electric current and the electrical anisotropy of a CFRP laminate, and conducted a falling-weight impact test to verify the validity of the proposed method. As a result, we succeeded in localizing the collision of the charged body in sufficiently high spatial resolution using the proposed system.</p>

DOI： 10.1299/transjsme.16-00237

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesa.2016.07.008

J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/mej.15-00491

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Experimental Mechanics  

This paper introduces "Tapping AE method" which is a new Non-destructive testing method for Carbon fiber reinforced plastic (CFRP). Although it has many advantages, internal damage easily occurs in CFRP components even by a small out-of-plane load. The typical non-destructive methods for CFRP are ultrasonic testing (UT) and tap testing. Although UT has high detectability, UT is a time and cost consuming method. On the other hand, tapping method is a quick and easy way to conduct, although, the detectability is insufficient. The aim of developing tapping AE method is realizing high-detectability tap testing. In Tapping AE method, the specimen is tapped by a hammer and secondary AE emitted from the damages are measured by AE sensor installed in the hammer during the hammer tapping. In order to evaluate feasibility of tapping AE method, we developed tapping AE system. The test was applied to a cross-ply CFRP laminate with and without internal damages. During the test, we observed secondary AE signals from the damaged specimen. New parameter, RMSratio was defined to evaluate secondary AE signals. Compared with the result of traditional tapping method using contact duration, the result of proposed method using RMSratio shows high detectability.

DOI： 10.11395/jjsem.15.175

CiNii Books

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesa.2014.08.010

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijadhadh.2015.03.003

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesa.2015.01.031

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compscitech.2014.12.013

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ndteint.2015.05.009

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.11395/jjsem.15.200

J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ndteint.2015.04.005

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compstruct.2015.07.028

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compstruct.2015.04.020

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4236/ojcm.2015.53009

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4236/ojcm.2015.54013

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.11421/jsces.2014.20140003

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science Japan  

DOI： 10.2472/jsms.63.331

Scopus

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Language：English   Publishing type：Research paper (international conference proceedings)  

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

High-temperature water stress corrosion cracking has high tensile stress sensitivity, and its growth rate has been evaluated using the stress intensity factor, which is a linear fracture mechanics parameter. Stress corrosion cracking mainly occurs and propagates around welded metals or heat-affected zones. These regions have complex residual stress distributions and yield strength distributions because of input heat effects. The authors previously reported that the stress intensity factor becomes inapplicable when steep residual stress distributions or yield strength distributions occur along the crack propagation path, because small-scale yielding conditions deviate around those distributions. Here, when the stress intensity factor is modified by considering these distributions, the modified stress intensity factor may be used for crack growth evaluation for large-scale yielding. The authors previously proposed a modified stress intensity factor incorporating the stress distribution or yield strength distribution in front of the crack using the rate of change of stress intensity factor and yield strength. However, the applicable range of modified stress intensity factor for large-scale yielding was not clarified. In this study, the range was analytically investigated by comparison with the J-integral solution. A three-point bending specimen with parallel surface crack was adopted as the analytical model and the stress intensity factor, modified stress intensity factor and equivalent stress intensity factor derived from the J-integral were calculated and compared under large-scale yielding conditions. The modified stress intensity was closer to the equivalent stress intensity factor when compared with the stress intensity factor. If deviation from the J-integral solution is acceptable up to 2%, the modified stress intensity factor is applicable up to 30% of the J-integral limit, while the stress intensity factor is applicable up to 10%. These results showed that the modified stress intensity factor can be applied even when the yielding scale exceeds the small-scale yielding criterion.

DOI： 10.1299/mej.2014smm0009

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Publishing type：Research paper (scientific journal)  

DOI： 10.4236/ojcm.2014.41003

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesb.2013.10.047

Web of Science

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/transjsme.2014smm0084

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/09243046.2013.832829

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4236/ojcm.2014.43015

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/mej.2014smm0030

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4236/ojcm.2014.43016

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5139/IJASS.2013.14.4.350

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/09243046.2013.805502

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesa.2012.09.014

Web of Science

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.79.1009

Scopus

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.79.555

Scopus

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.engfracmech.2013.07.019

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/09243046.2013.801822

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijadhadh.2013.01.008

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3144/expresspolymlett.2013.26

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/jsmemecj.2013._J046012-1

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesa.2011.09.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

Quick and automatic inspection of carbon fiber reinforced polymer (CFRP) aircraft after each flight would reduce the safety factor and allow for more flights. Visualization of impact damage was developed in an earlier study as an automatic self-monitoring method. The damaged area was visualized by selective and intense resistive heating based on its decreased through-thickness resistivity compared to undamaged areas. In the present study, the lightning protection system of a composite aircraft was used to apply a uniform electrical current distribution and electric heat to a large structure. Subsequent coupled thermal-electrical analyses showed that even small indentations (depth <0.15 mm) could be relatively easily detected in structures about 1 m in size.

DOI： 10.1299/jmmp.6.213

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

From a traffic safety point of view, there is an urgent need for intelligent tires which can optimize braking control by estimating the slip ratio and friction coefficient between a road surface and an automobile tire. The present study develops concurrent monitoring of frictional and vertical loads applied to the tires from the inner tire strain data for estimating the road/tire friction coefficient, which enables optimization of vehicle control and implementation of a road condition warning system. The tire strain is obtained using a three-dimensional digital image correlation method with a single wireless CCD camera attached to the wheel rim inside the tire. The procedures of the applied load estimation decompose the measured strain into the frictional and vertical strain components using their symmetrical and anti-symmetrical characteristics. Static tire rotation tests were carried out, and the applied loads were estimated from the inner tire surface strain distribution. Compared with the actual applied loads measured from strain gages attached to the experimental apparatus, it was confirmed that the vertical and frictional loads can be estimated independently with adequate accuracy.

DOI： 10.1299/jmmp.6.935

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.78.458

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.engfracmech.2012.08.011

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesa.2011.12.024

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.6.1053

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.6.1042

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.6.1062

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesa.2011.01.014

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

The previous study employs delamination detection in CFRP laminates using statistical analysis of temperature characteristic of resistance to prevent electrical resistance changes caused by damages of electrical contact at electrodes. A statistical analysis method discriminates the temperature characteristic of resistance of the damaged structure from that of the intact structure. To detect delaminations without learning processes, a new method which compares the electrical resistances at high temperature with those at low temperature is developed here. The new method has applicability to existing structures and can also detect initial defects. The present study employs the new method for detecting delaminations and initial defects in quasi-isotropic-plied CFRP plates. The detection limit of delamination and the effectiveness of detecting initial defects are experimentally investigated, and the effect of electrode damage on the diagnosis is discussed here.

DOI： 10.1299/kikaia.77.181

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s11465-011-0231-1

Scopus

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.compositesa.2011.03.004

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.5.44

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jcst.5.26.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.5.33

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society for Experimental Mechanics  

This paper describes the measurement of average strain, strain distribution and vibration of a cantilever beam made of Carbon Fiber Reinforced Plastics (CFRP), using a single Fibre Bragg Grating (FBG) sensor mounted on the beam surface. Average strain is determined from the displacement of the peak wavelength of reflected spectrum from the FBG sensor. Two unstrained reference FBG sensors were used to compensate for temperature drift. Measured strains agree with those measured by a resistance foil strain gauge attached to the sample. Stress distributions are measured by monitoring the variation in the full width at half maximum (FWHM) values of the reflected spectrum, using a proposed optical analytical model, described in the paper. FWHM values were measured for both the cantilever test beam and for a reference beam, loaded using a four-point bending rig. The trend of the stress distribution for the test beam matches with our analytical model, however with a relatively large noise present in the experimentally determined data. The vibration of a cantilever beam was measured by temporal analysis of the peak reflection wavelength. This technique is very stable as measurements are not affected by variations in the signal amplitude. Finally an application of FBG sensors for damage detection of CFRP plates, by measuring the natural frequency, is demonstrated. With small defects of different sizes applied to the CFRP plate, the natural frequency decreased with damage size.

DOI： 10.1007/s11340-011-9467-2

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人日本機械学会  

DOI： 10.1299/kikaia.76.961

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 腐食防食学会  

Temperature dependency of external stress corrosion cracking (ESCC) of 304 stainless steel was examined with CT specimens. Maximum ESCC propagation rates appeared in the early phase of ESCC propagation. ESCC propagation rates generally became smaller as testing time advance. Temperature dependency of maximum ESCC propagation rate was analyzed with Arrhenius plot, and apparent activation energy was similar to that of SCC in chloride solutions. Temperature dependency of macroscopic ESCC incubation time was different from that of ESCC propagation rate. Anodic current density of 304 stainless steel was also examined by anodic polarization measurement. Temperature dependency of critical current density of active state in artificial sea water solution of pH=1.3 was similar to that of ESCC propagation rate.

DOI： 10.3323/jcorr.59.430

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.4.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.4.610

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.4.711

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.4.864

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.4.658

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.4.658

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

DOI： 10.1299/jmmp.4.864

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

Intelligent tires, also known as smart tires, are equipped with sensors to monitor the strain of the interior surface and the rolling radius of tire, and are expected to improve the reliability of tires and tire control systems such as anti-lock braking systems (ABS). However, the high stiffness of an attached sensor like a strain gauge causes debonding of sensors from tire rubber. In the present study, a novel optical method is used for the concurrent monitoring of in-plane strain and out-of-plane displacement (rolling radius) utilizing the non-planar surface of the monitoring object. The optical method enables noncontact measurement of strain distribution. The in-plane strain and out-of-plane displacement are calculated by using image processing with an image of the interior surface of tire that is taken with a single CCD camera fixed on a wheel rim. This new monitoring system is applied to an aluminum beam and a commercially available radial tire. As a result, the monitoring system provides concurrent measurement, of in-plane strain, out-of-plane displacement and tire pressure, and is shown to be effective as the monitoring system for the intelligent tires.

DOI： 10.1299/kikaia.75.1269

CiNii Books

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

It is important to evaluate the integrity of composite overwrapped pressure vessels (COPVs) used for space applications. In this study, applicability of acoustic emission (AE) monitoring to the integrity evaluation of COPV materials was evaluated by using coupon-level specimens. It was found that by evaluating emissions during load-hold and relationship between AE signal peak amplitude and duration, damage occurrences during the test can be monitored. We also found that Kaiser effect and Felicity effect can be used for evaluating previously induced dam ages. Detectable minimum damage size for previously induced damage by AE method may be same or less than those by ultrasonic testing.

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

It is important to evaluate the integrity of composite overwrapped pressure vessels (COPVs) used for space applications. In order to examine applicability of acoustic emission testing (AT) for the evaluation, AE signals were monitored during the pressurization test of a COPV before and after an impact test. The impact test of 17-J energy was conducted by using a drop-weight impact tester to simulate machine-tool drop. A large number of emissions were monitored by the AE channel nearest the impact point. In addition, the characteristics of AE signals detected nearest the impact point were different from those by other channels. From these results, it is assumed that AT can be used for the qualitative integrity evaluation of COPVs. On the other hand, to realize the quantitative integrity evaluation, it is essential to make data base of AE parameters.

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, usefulness of lamb waves generated by chirp signals for NDI was examined. The target for the inspection is wall parts of composite propellant tanks. We first studied characteristics of lamb waves propagated around delamination zone by computer simulation. Then, the damage inspection using lamb waves generated by chirp signals was conducted on the composite plates with artificial damaged zone. When the sensor is on the damaged zone, maximum amplitude became 17% of those at sound zone. On the other hand, when the damage zone was between two sensors, scattered lamb waves were monitored. Finally damage inspection system was developed by utilizing these characteristics of lamb waves.

DOI： 10.11395/jjsem.8.65

CiNii Books

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

The impact damage threshold to cause internal damage in cross-ply CFRP laminates has been determined, by monitoring dynamic surface strain and Lamb-wave AE (Acoustic Emission) along with the impact force history in SACMA-type impact tests. Four types of cross-ply CFRP plates ([0o n /90o n]sym., n=4,6,8,10) are impacted with a spherical steel tup, 16 mm diameter, at 0.8 and 1 m/s. Surface strain of a test laminate is measured using a strain gauge and Lamb-wave AE signals are monitored by small AE sensors on both surfaces. The time history of surface strain matches with the impact force history when no damage occurs as predicted by theory of impact dynamics. Here, only impact-induced AE (or Impact AE) is obtained when the impact tup contacts the specimen. When internal fracture occurs, measured strain history deviated from that expected from the dynamic force and both Impact AE and fracture-induced AE (Fracture AE) are detected. Fracture AE is detected when the dynamic force and strain history indicates the initiation of internal CFRP damage. Impact damage threshold values for the four types of cross-ply CFRPs are measured by comparing the impact force, strain and Fracture AE. Initial AE signals monitored simultaneously on both sample surfaces are symmetric Lamb waves. Wave simulation analysis has revealed the nature of the onset of fracture to be the matrix cracking of the center plies. Complex AE signals following the initial fracture for a few ms are expected to be from delamination damage, which was confirmed with an ultrasonic C-scan study.

DOI： 10.1299/jmmp.2.1547

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/jinstmet.71.291

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Acoustic Emission Working Group  

The impact damage of CFRP plates under impact load was evaluated using recording of AE, load and strain history. The threshold or critical impact force to cause internal damage in cross-ply CFRP laminates was determined using dynamic surface strain and Lamb-wave AE along with the impact force history. Loading was conducted in SACMA-type impact tests at 0.8 and 1-m/s velocity. Four types of cross-ply CFRP plates ([0o n/90o n]s, n = 4-10) are impacted with a spherical steel-tup. Lamb-wave AE signals were detected by small AE sensors on both surfaces. Polarity of AE signals detected by both sensors are used in studying the progression of fracture. Only impact-induced AE (or Impact-AE) is obtained when the impact tup contacts the specimen at a lower speed. When internal fracture occurs, both Impact-AE and fracture-induced AE (Fracture-AE) were detected. The nature of Fracture-AE is examined in this study in con junction with ultrasonic C-scan and surface evaluation. AE monitoring on both surfaces enabled us to clearly separate the S0 and A0 modes of Lamb-wave AE signals. Most of strong AE signals correlated with matrix fracture source, while other damages had no associated distinctive events.

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Acoustic Emission Working Group  

We have proposed a control method for plastic-region tightening of bolts using AE method. In this paper, in order to investigate the validity of the tightening control by AE method, the tightening test in simulated factory environment was conducted and both tightening accuracy and variations were compared with those by conventional control methods. The results show that AE method is more effective for plastic-region bolt tightening control than the conven tional methods. Finally, a new system using a Maharanobis distance for controlling plas tic-region bolt tightening by AE method was developed.

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/jinstmet.70.1012

Web of Science

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Stress corrosion cracking (SCC) susceptibility of commercial type 316L stainless steel (SS) and 316 SS hot rolled plates was examined by the creviced bent beam method in oxygenated high temperature water at 561 K. Asreceived type 316L SS and 316 SS showed the highest susceptibility to SCC at the cold rolling reductions of 10% and 20%, respectively. Aging treatment on type 316L SS had a beneficial effect of mitigating SCC, although the same aging treatment degraded SCC resistance of type 316 SS in a certain temperature range probably because of the combined effect of sensitization.<br>The fracture surface of as-received and cold rolled type 316L SS and type 316 SS consisted mainly of inter-granular SCC with a small fraction of trans-granular SCC similar to those observed in the actual components. Heavily cold rolled Type 316 SS showed a large fraction of trans-granular SCC even in sensitized condition, suggesting that the heavy cold rolling formed active paths much sensitive to SCC than Cr depleted zone in crystal grains.<br>It was suggested from SEM observation that the crack growth process on specimen surface would contain coalition of several smaller cracks to one larger crack in addition to the growth of each crack.

DOI： 10.3323/jcorr.55.399

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Acoustic Emission Working Group  

AE source location is widely conducted during fracture monitoring of industrial structures. However, special techniques are required for thin structures due to the dispersive nature of plate wave AE. We have suggested frequency filtering algorithm utilizing a fast continuous wavelet transform for the source location in thin structures. By utilizing this method, the source location of thin structures can be conducted with good location accuracy. The Gabor function had been used as a mother wavelet in the previous study, but the effectiveness of other mother wavelets or frequency filtering algorithms had not been examined. In this study, the usefulness of Mexican hat wavelet, French hat wavelet, Haar wavelet, Gabor function wavelet, Harmonic wavelet and Butterworth filter for source location on thin structures were investigated. The Gabor function wavelet produced the most accurate source location compared to the other frequency filtering algorithms.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

Ultrasonic flaw sizing is important issue for remaining life prediction of industrial plants. Time-of-Flight Diffraction (TOFD) method is recognized as one of the most accurate flaw sizing method. However, to measure the crack height accurately, the crack must be symmetrically placed between transmitter and receiver. When the crack do not exist such position, the B-scan is required for accurate crack sizing. By the way, if additional transmitter or reciever is added to the system, the crack location and height can be estimated without B-scan. In this study, we examined the 4 sensor TOFD method which utilizes two transmitters and two receivers. In the result, the crack location and height can be estimated by 4 sensor TOFD method. However, the estimation errors were large due to the low SN ratio of received signal. Then we applied the pulse compression technique to the 4 sensor TOFD method for improving SN ratio of received signal. In the result, the SN ratio was enhanced about 11 dB by the pulse compression. The average location on error is reduced from 2.49 mm to 1.13 mm, and the average depth estimation error is reduced from 0.28 mm to 0.21 mm.

DOI： 10.1299/kikaia.72.2030

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/jinstmet.69.1049

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

Evaluation methods of thickness and interfacial soundness of polymer-lining on steel substrate were developed. The dispersive Rayleigh mode wave and The leaky Interfacial Compressional Wave (LICW) propagating along the lining surface or interface of a lining/substrate were utilized. Propagation characteristics of the waves were experimentally studied. Two methods of estimating lining thickness were proposed and experimentally verified using the dispersion relation of the Rayleigh mode wave and the propagation characteristic of the LICW. Size and location of the delamination portion can be determined utilizing the propagation characteristics of the LICW and Lamb wave via the delaminated lining layer.

DOI： 10.11396/jjsndi.54.252

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Acoustic Emission Working Group  

In this study, we developed a real-time executing source location system for anisotropic thin structures such as CFRP (Carbon Fiber Reinforced Plastics) tanks. The system consists of AE sensors, an A/D converter on a PC and a computer with proprietary software. We suggest two algorithms to realize the real-time executing source location. The first algorithm is a frequency filtering algorithm utilizing a fast continuous wavelet transform. The second algorithm is a fast source location calculation algorithm for unidirectional anisotropic structures. In the second algorithm, the affine coordinate transform is used. The calculation time for each source location is reduced to 1ess than 15 ms with reasonable accuracy

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

Damage monitoring of impacted materials by Acoustic Emission (AE) is useful for integrity evaluation. The monitoring is, however, generally difficult due to overlapping of AE signals by impact and damage. The autors proposed a new method to monitor crack generation by extracting the fracture-induced AE signals from strong AE signals produced by impact. Here, AE sensors were mounted on two end faces to minimize the effect of impact -induced AE. The impact testing was conducted for a 5mm-thick PMMA plate. Crack initiation was successfully monitored by the proposed method. Crack kinetics (opening speed and volume) was estimated by waveform simulation of the S0-Lamb packet using experimental overall transfer function of the system. The impact force history was also estimated using impact induced AE detected by a sensor on the impact surface.

DOI： 10.11396/jjsndi.53.230

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to estimate locations of micro-cracks in CFRP-tank during pressurization testing, we developed a source location method for utilizing AE signals. A 4-ch system of 150kHz resonant-type AE sensors was used for the source location. We first investigated the orientation dependence of AE signals in the tank by using artificial sources. Lamb-mode dispersive AE signals were monitored and arrival times to the sensor were defined by the times to maximum 90kHz-wavelet coefficients from each signal. We then investigated the effect of AE signals via liquid in the tank on source location results. Damage monitoring zone was set to the tank, and AE signals from non-monitoring zone were separated from those from monitoring zone by duration. Source location algorithm was proposed in this paper and accuracy of proposed method was discussed using artificial sources at variable points both in the monitoring and non-monitoring zone. Eighty percent of AE signals from non-monitoring zone were correctly separated from AE signals from monitoring zone. Source location of artificial source was estimated by the proposed method. Location of artificial source was identified with average error of 17.8 [mm] except 4 large error points.

DOI： 10.11395/jjsem2001.3.266

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate fracture modes and timing for two types of CFRP plates during cryogenic shock testing, Acoustic Emission (AE) monitoring was conducted. No damage was observed for the specimen that made of heat-resistant matrix, however, thirty-nine matrix cracks were observed for the other specimen. Several cracks were observed even at the location where temperature differences on both surfaces were small. The AE signals were classified into three types by waveform characteristics according to the damage behavior. After that, three fracture modes of matrix crack, delamination and transverse cracks were simulated by pulse-laser irradiation to the CFRP plate and the detected AE signals were compared to estimate those obtained at cryogenic shock testing. The number of the AE signals linearly increased untill the LN2 disappeared from the cooling cell. Then, we conducted the vertical immersion test to examine the influence of cooling temperature to the damage occurrences. At temperatures lower than 228K, matrix cracks initiated at the specimen surface. At 213K, large number of AE signals due to matrix crack and few number of AE signals due to delamination and transverse crack were observed. At 77K, large number of AE signals caused by three types of fractures was detected.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

For long time, numerous efforts have been made to find a way of performing a comprehensive three-dimensional photoelastic analysis with a model intact, even so the problem is still far from being solved completely because of thedifficulties how to realize the integrated fringe patterns obtained in measurements under continuous rotation of theprineipal birefringence axes. The final goal of this study is aimed at the establishment of new technique for analysis of internal stress distributlon in three-dimensional objects, but in this paper, the authors arrange two glass disks having a different stress state respectively in series and make attempt to separate stress states in each disks using an inverse analysis method. As the result, phase diffbrence and azimuth angle of two disks is successfully separated over the whole field.

DOI： 10.11395/jjsem2001.2.264

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.6089/jscm.28.66

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Study aims to estimate the impact force history and correlate it with damage occurrence in a cross-ply CFRP plate impacted by flying steel ball (φ7mm) at 10 to 45m/s velocities. Both the plate deflection and Lamb AE waves were monitored for 2mm thick [0°4/90°4]sym. cross-ply CFRP plate. We estimated the impact force from the plate deflection and the force history by the simplex-assisted Lamb waveform simulation, and compared with that calculated from energy balance and spring-mass models. The time history estimated by the Lamb waveform simulation agreed well with that calculated by the spring-mass model, however the force amplitude estimated by Lamb wave is 3.5 times smaller than that by the spring-mass model, but about half that by energy balance model. The maximum force amplitude estimated from the plate deflection agreed with that by the energy balance model at ball velocities below 20m/s, but the former significantly deviated at ball velocities higher than 30m/s at which large delamination occurred. Data deviation indicates a possibility of determining the critical ball velocity to cause serious internal damage. We discuss the detail of agreement and disagreement between the experimental data and models.

DOI： 10.2472/jsms.50.1036

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1023/a:1012573801510

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

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Language：English   Publishing type：Research paper (scientific journal)  

Web of Science

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/s0963-8695(99)00030-4

Web of Science

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

CiNii Books

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Soc of Corrosion Engineering  

DOI： 10.3323/jcorr1991.48.733

Scopus

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Scociety of Mechanical Engineers  

Laser surface acoustic waves (SAW) were utilized to detect the artificial subsurface lateral delamination in Unidirectional (UD)-GFRP. The amplitude distribution of the Rayleigh and Lamb waves over the surface was obtained by the wavelet transform of the SAW monitored by a heterodyne-type laser interferometer and was successfully utilized to detect the subsurface delamination area. The depth of delamination was accurately estimated by analysis of the phase velocity dispersion of the SAW.

DOI： 10.1299/kikaia.63.1499

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CiNii Books

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CiNii Books

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J-GLOBAL

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J-GLOBAL

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Carbon fiber reinforced polymer (CFRP) laminates have been getting adopted as structural components for aircrafts due to their high mechanical performances. For the purpose of the evaluation of damage caused by a lightning strike, electric current analysis for CFRP laminates is indispensable. The authors have already proposed the analysis method using orthotropic electric potential function, which is applicable to the large structure that cannot be dealt with by general numerical methods such as FEM and FDM. In the case of unidirectional and cross-ply CFRP laminates, the effectiveness of this method has already been shown. The actual CFRP structures, however, have 45°, -45° carbon fiber plies in many cases. The present study proposes the improved method which can be applicable to the laminates having 45°, -45° plies. The effectiveness of this method was shown through the comparison with a numerical method.

CiNii Books

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J-GLOBAL

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CiNii Books

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J-GLOBAL

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

This paper introduces "Tapping AE method" which is a new NDT method for CFRP. CFRP has a large number of advantages, although, internal damage easily occurs in it when impact load is applied. The typical NDT method to detect internal damages of CFRP are ultrasonic testing and tap testing. Although UT is reliable method for its high detectability, UT is a time and cost consuming method. On the other hand, tapping method is a quick and easy way to conduct, although, the detectability of the method is insufficient for main component materials. The aim of developing tapping AE method is realizing high-detectability tap testing. In Tapping AE method, the specimen is tapped by a hammer and secondary AE emitted from the damages are measured by AE sensor installed in the hammer during the hammer tapping. In order to evaluate feasibility of tapping AE method, we developed tapping AE system. The test was applied to a cross-ply CFRP laminate with and without internal damages. During the test, secondary AE signals were successfully observed.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

For the structural integrity assessment of the sandwich structural leaf spring installed on the rolling stock bogie "efWING", Electrical Resistance Change Method using the electrical conductivity of carbon fiber has been studied. In the present study, electrical resistance change of fatigue-loaded test coupons is experimentally measured and an inner damage is captured by ultrasonic testing. The relationship between electrical resistance and an inner damage is analytically investigated using FE analysis. As a result, the study shows the electrode producing a high current density in through-thickness direction is effective to detect an inner damage.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

This paper introduces a new technique to reconstruct Lamb wave ultrasonic tomography with manual transmitter scanning. By this technique, ultrasonic tomographic image can be obtained using only 4 receivers and 1 transmitter without a scanner or an encoder. The image is reconstructed by determining the transmitter position (x,y) by source location method and estimating an existence of defects between the transmitter and the receivers from amplitude-ratio of Ao mode to So mode of lamb wave. Lamb wave tomographic image was successfully reconstructed for an Aluminum plate with artificial defects by proposed method.

CiNii Books

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

Acoustic Emission Testing (AT) is one of the non-destructive testing methods which are widely used in engineering fields. Final goal of monitoring AE phenomena is to estimate characteristics of AE sources and to provide beneficial information to prevent fatal fracture. It is know that b-value is not changed by propagation length from the AE sources to AE sensors. Although, the effects of the frequency dependence on AE attenuation to b-value is not discussed in details by any researcher. In this research, we conducted the simulation with two conditions. First condition assumes AE source contains single frequency of 45 or 65 kHz, and the other condition assumes the source composed of 25 kHz, 45 kHz and 65 kHz. As a results, b-value is changed by propagation length when assuming AE sources with multiple frequencies. The cause of changing b-value is due to non-linear behavior of AE attenuation.

CiNii Books

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CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

This paper introduces a new real-time image ultrasound technique for thin-wall structure in which the scanning of the ultrasound transmitter is carried out by hand. By this technique, we can get the ultrasound-image without a scanner or an encoder, and test a thin-wall structure faster than by ultrasonic pulse-echo method. Existence or nonexistence of defects is estimated by monitoring the amplitude-ratio of A_0 mode to S_0 mode of lamb wave between the ultrasound transmitter and the receiver. In addition, the image is constructed by determining the transmitter position (x,y) by source location method. The damaged image was successfully constructed for a thinning made on Aluminum plate by proposed method.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Carbon Fiber Reinforced Polymers (CFRPs) are becoming widespread for their high specific strength and many other advantages. However, a small out-of-plane impact load can easily cause internal defects in CFRP plates. Although ultrasonic inspection scheme is generally used to find and estimate location and size of defects, the method usually requires both long inspection time and a large cost. Accordingly, a low-cost and in-situ monitoring system for impact load is required to assure safety of CFRP components. When applying an impact load to electric conductive materials such as a CFRP plate, an electric current flows in the plate. We conducted impact tests and finite element analyses to elucidate the mechanism of electric current generation by electrostatic induction when the charged impactor approaches the plate. In addition, we proposed a system made of a CFRP plate to identify the impact location of charged impactor from measured electric current.

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CiNii Books

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J-GLOBAL

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CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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There is a possibility that the crack growth rate of stress corrosion cracking and fatigue crack depend on the value of ∂K/∂a (differential term of stress intensity factor) as well as stress intensity factor K. In this study, the effect of ∂K/∂a on crack growth rate was investigated during the fatigue test. Two types of specimens were prepared. One is CT specimen of which K increases under constant loading. The other is CDCB specimen of which K is constant. The effect of ∂K/∂a was clarified by comparing the CT specimen and CDCB specimen under same stress intensity factor. In addition, ΔK corrections considering ∂K/∂a were conducted for CT specimens. As a result, the crack growth rates in CT specimens were larger than CDCB specimens in the same ΔK. Corrected ΔK considering ∂K/∂a is mostly coincides with the value of the CDCB specimen. From those results, the crack growth rate varied due to the effect of ∂K/∂a in fatigue crack propagation was experimentally clarified. In addition, elimination of the influence of ∂K/∂a is possible by ΔK correction.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Weight saving structures are recently demanded to reduce the energy consumption. Even for the automobile structures, Carbon Fiber Reinforced Plastics (CFRP) have been applied in these days. Hybrid car or Electrical Vehicle requires an electrical generator and an electrical condenser. Recently, the capacitors are tried to be integrated in composite structures such as carbon/epoxy laminates to save the weight and space: the structures are called CFRP structural capacitor, which has dielectric layer between CFRP laminates. Final goal of this study is to apply this structure into automotive outer panel made of CFRP. In order to keep capacitance and mechanical properties high, dielectric layer must be thin. But thin dielectric layer tends to cause continuity between CFRP electrodes. In the present study, we propose a manufacturing method of CFRP structural capacitor and the desirable condition of the method to prevent the continuity of electrodes and

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A new finite heterogeneous element consisting of sliced microstructures (FHES) is applied in a multi-scale technique. The FHES represents a heterogeneous material with microscopic constituents without homogenization or microscopic finite element analysis. A representative volume element extracted from a heterogeneous structure is thinly sliced. Each slice is modeled as a combined spring to calculate properties of the FHES. Each FHES has the same number of nodes as an ordinary finite element, and the macroscopic analysis cost is the same as that for ordinary finite element analysis. However, the FHES retains information about the microscopic material layout (i.e., the distribution of a material's property) in itself that is lost during homogenization. In the proposed approach, materials are not homogenized. The FHES does not have a constant (homogenized) material property and can "change stiffness" depending on its deformation behavior. This reduces error due to coarse-graming, and allows us to calculate the macroscopic deformation behavior with sufficient accuracy even if a large gradient of strain is generated in the macroscopic field. The novelty of the research is the development of rational heterogeneous finite elements. The paper presents the theory behind the FHES and its practical application to a linear elastic problem.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Composite materials have been widely used for primary structures of aircraft, and a rapid diagnosis method for large composite structures like aircraft components is required. In this study, a new inspection method using a lightning protection shield (LPS) as a load sensor and its wiring is proposed. Proposed load sensor is composed of copper plate used for LPS (upper layer), circuits (lower layer) and silicone rubber sheet used as support material between these two layers. The circuit consists of copper wires which are arranged in the direction of x-axis and which are arranged in the direction of y-axis. When an aircraft structure is impacted, copper plate of the sensor (upper layer) makes contact with wires of lower layer. Therefore a new electrical path occurs between the copper plate and circuit at the impacted point only while the colliding object is pressing the copper layer. A voltage gradient is applied to copper wires by Nichrome wire connected perpendicularly to the copper wires of each direction. The coordinates of the impact point can be identified by the touchpad techniques. To verily the practicability of the proposed sensor, impact load tests were conducted with the proposed sensor of 25mm×225mm and impacted position was identified within an error of less than 10.3mm.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Carbon fiber reinforced polymer (CFRP) composites have higher specific strength and specific stiffness than conventional metallic materials. However, the CFRP structures are easily damaged by impact loading. It is quite difficult to detect internal damages caused by impacts by visual inspection. In the present paper, self-sensing time-domain reflectometry (TDR) is proposed as a damage detection method for large CFRP structures. In the TDR, a set of high-frequency impulse signals is applied to a structure and damage location is calculated from difference in time of arrival between an input signal and reflected signal from the structure end or the damage. The experiment using TDR is conducted in this paper. It is the experiment for detection of impact damage in a long quasi-isotropic CFRP (1600 mm^L×200 mm^W, [0/+45/0/-45/90/+45/0/-45/ 90]s) in the fiber direction. Microstrip Line (MSL) structure is utilized for damage detection of CFRP. It is the structure which is arranged the dielectric (Glass fiber reinforced polymer, GFRP) on CFRP and the five copper lines as waveguide of electric pulse on the top. Copper meshes used for lightning protection in composite aircraft are arranged on copper lines of MSL which are not the target for measurement during TDR measurement in order to investigate that TDR could detected impact damage even if copper meshes exist around MSL. As a result, the experiments indicated that the TDR could detect impact damage on the copper line of MSL which could be used as lightning protection system.

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In recent years, thermoplastic CFRP attracts considerable attention especially in aviation and automobile industries due to weldability of thermoplastic CFRP. Ultrasonic testing (UT) is commonly adopted as a testing method for inspecting weld parts although time and cost on UT is thought to be problematic. Since eddy current testing (ET) is used for rapid and non-contact inspection on electrically conductive materials, this paper presents an eddy current based approach for detecting defects in thermoplastic CFRP welded zones. However, it is difficult for conventional ET to detect delamination which is parallel to eddy current although delamination is one of the common forms of weld defect. To detect delamination in thermoplastic CFRP welded zones, new eddy current based approach which utilizes temperature characteristic of electrical conductivity is proposed. The proposal consists of two steps. Firstly, temperature difference between intact zones and defective zones is caused by heating the one side of the weld part. Secondly, the temperature difference is detected by ET utilizing temperature dependency of electrical conductivity.

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A COPV (Composite Overwrapped Pressure Vessel) is consisting of a thin metallic liner wrapped with a fiber composite. The outer side CFRP layers bear the load due to internal pressure, and the inside liner provides a barrier between the fluid and the composite. Because of its high specific strength compared to metal pressure vessel, COPV have been applied to the field of aerospace. If it suffers impact load such as by falling tools, both CFRP and liner cause the impact failure, and a dent remains in liner by metal plastic deformation. Usually, the liner deforms elastically in MEOP (Maximum Expected Operating Pressure), but in the part of liner dent, there is a possibility of plastic deformation by adding the bending moment as well as the load due to internal pressure. If tensile and compressive plastic deformation repeats by pressurizing and depressurizing, the ratchetting plastic deformation occurs and plastic strain is accumulated in liner dent. This study discusses the ratchettig defomation of the COPV liner, and investigates the presence of ratcheting by FEM.

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Welds and heat affected zones have the distribution of the residual stress or the yield strength. The crack growth evaluation is conventionally conducted using stress intensity factor in those regions. However, the stress intensity factor may be invalid when the residual stress distribution or yield strength distribution changes in the vicinity of a crack tip. When the distributions exist, the crack growth evaluation should be conducted using a parameter considering the elastoplastic behavior near the crack tip. For that purpose, the authors proposed new correction method of the stress intensity factor using a differential term of that. The new method was demonstrated through the case study for stress corrosion cracking in a high temperature water environment.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Acoustic emission (AE) testing is one of the major nondestructive testing (NDT) techniques, and it can be used as the real-time monitoring method for the purpose of detecting fatigue damages. However, AE testing data for steels during the low-cycle fatigue test is rarely reported. In this study, AE monitoring was conducted during low-cycle fatigue test for austenitic stainless steel with the aim of detecting fatigue damages and identifying the source of AE. Those AE occurred in the process of increscent phase which is loading under tensile and unloading under compression and the contact of the crack surfaces were observed at the increscent phase. This means that friction of the crack surfaces induced AE. Therefore, the potential for monitoring low-cycle fatigue crack was demonstrated by focusing on the friction-induced AE (secondary AE).

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During Resin transfer molding (RTM) process for manufacturing composites, entrapped air may remain as void in a part to bring significant decrease of the mechanical properties. In the past, it has been presented that amount of the void formation depends on velocity of resin flow. However, in the case that an anisotropic fabric is applied, directions of the resin flow may also affect on the void formation. In this paper, the effect of anisotropy of fiber on void generation was examined analytically and experimentally. Finally, good agreement was obtained between results of them.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Composite materials have been widely used for primary structures of aircraft, and a rapid diagnosis method for large composite structures like aircraft components is required. In this study, a new inspection method using a lightning protection shield (LPS) as a load sensor and its wiring is proposed. The proposed sensor identifies the coordinates of the impact point by the touchpad techniques. To verify the practicability of the proposed sensor, impact load tests were conducted with the proposed sensor of 360mmx225mm. The impacted position was identified within an error of 10.3mm.

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Language：Japanese   Publisher：日本複合材料学会  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Carbon fiber reinforced polymer (CFRP) composites have higher specific strength and specific stiffness than conventional metallic materials. The CFRP structures, however, are easily damaged by impact loading. It is quite difficult to detect internal damages caused by impacts by visual inspection. In the present paper, self-sensing time-frequency-domain reflectometry (TFDR) is proposed as a damage detection method for large CFRP structures. In the TFDR a set of high-frequency burst signals is applied to a structure and damage location is calculated from difference in time of arrival between an input signal and reflected signal from the structure end. By using several signals with different frequencies, other information such as dimensions of damage can be obtained. This is one of the great advantages to using the frequency domain reflectometry. The TFDR uses both methods; one estimates damage location and the other identifies its dimensions. The purpose of this study is to verify the applicability of the TFDR to CFRP structures. In the TFDR, after experiment for damage detection using the time domain reflectometry (TDR) with electromagnetic waves flowing in a long UD CFRP (1980 mm×120 mm) in the transverse direction, the frequency characteristics of the wave in the CFRP structure are investigated by the finite difference time domain (FDTD) analysis. As a result, the experiment indicated that the TDR could detect a notch in the CFRP using waves flowing in the transverse direction. The electromagnetic analyses showed that the TFDR was able to detect damage and identify its location and dimensions of CFRP structures.

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The stress intensity factor is a fracture mechanics parameter that describes the stress field around a crack tip. When the stress intensity factor is used as a fracture mechanics parameter, the small-scale yielding condition in which the plastic-zone size near the crack tip should be sufficiently small relative to the crack length must be satisfied. When a hardness distribution exists near a crack tip, the potential exists to deviate from the conditions. In this study, yield stress distributions as a hardness distribution which are given Gaussian distribution along the crack propagation path are considered in the crack propagation model based on the Dugdale model. The validity of the stress intensity factor around the yield stress distribution are investigated by conducting numerical analysis. As a result, when the magnitude of the yield stress change within distribution is large, small-scale yielding conditions tend to be unsatisfied.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

This paper discusses optimum design of a stiffened composite panel, which is used in aerospace structures. Anisotropic thermal expansion coefficients of the composite laminates causes complicated deformation of the panel after the curing. In previous researches, stacking sequence optimizations were performed without considering thermal deformation: a response surface was used to obtain an objective function, and lamination parameters were sued as variables for the response surface of the objective function such as buckling load. However, the thermal deformation must be considered as a constraint factor for actual composite structures. In the present study, therefore, thermal deformation is dealt with as a constraint for a stacking sequence optimization problem. Three surrogate models of the thermal deformation are discussed here: a conventional method using lamination parameters; a new method using thermal coefficients; a modified new method As a result, the modified new method is shown to be effective for the surrogate model.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The Electrical Resistance Change Method (ERCM) is useful for inspection of CFRP (Carbon Fiber Reinforced Plastic) structures, because electrical conductivity of carbon fibers in them can be used as a sensor for damage detection. Fatigue damages need to be detected using the ERCM because these damages decrease residual strength and reliability of CFRP structures. This study experimentally deals with cyclic loading tests of CFRP laminates using the ERCM. Moreover, the mechanism of electrical resistance change caused by cyclic loading was investigated. First, the electrical resistance change was measured by four-probe method for CFRP laminates with stacking sequences of [0/±45/90]_s and [0_2/90_2]_s. As a result, the electrical resistance of CFRP laminates with the stacking sequence of [0/±45/90]_s decreased with the cycle number. By contrast, that with the stacking sequence of [0_2/90_2]_s increased with the cycle number. The mechanism of the resistance decrease of quasi-isotropic laminates under cyclic loading, which could have not been explained by the conventional theories, was revealed in this study. The test results indicate that residual strain in ±45° plies caused by cyclic loading increases fiber-fiber contact, which decreases resistance.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A rapid diagnosis method for composite aircraft is required. In this study, a new inspection method using a load sensor which also acts as a lightning protection shield (LPS) is proposed. The load sensor consists of upper layer and lower layer composed of an electrical circuit which has many pressure-sensitive elastomer pills in it. The upper layer is a copper mesh sheet acting as a LPS. The lower layer consists of two kinds of wires. One is high-electrical-resistance nichrome, and another is low-resistance copper. The pressure-sensitive pill changes from an electrical insulator into a conductor when it is compressed. When an impact load is applied to the sensor, the pressure-sensitive pill gives a new electrical path between the two layers at the load point. During the operation of the load sensor, a unidirectional gradient of electrical potential is applied to the lower layer. When a new electrical path is formed between the two layers by the load, potential of the upper layer comes to be equal to that of the indented part of the lower layer. Consequently, measuring the potential of the upper layer provides the X coordinate of the load point. After the X coordinate is acquired, the orthogonal potential gradient is applied to the lower layer to measure the Y coordinate. These XY coordinates can be evaluated within a few milliseconds. In addition, it comes possible to estimate the peak value of the load by measuring the electrical resistance of the pressure-sensitive pill.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, a new welding method which utilizes conductivity of CFRTP (Carbon fiber reinforced thermoplastic) is proposed. Electrical current is applied through the CFRTP single-lap joints in thickness direction. Since resistance of joining surface is the highest in the current path, the joining surface is preferentially heated by Joule heating. In this study, surface welding was conducted by the proposed method. By applying constant voltage of 10.3V, the joint-surfaces were heated above melting temperature of the material and were welded. In order to evaluate lap-shear strength (LSS) of welded joints, tensile lap-shear strength tests were conducted. As a result, LSS are 22.0MPa (CF Fabric/PEI) and 22.5MPa (CF Fabric/PPS). These strengths were comparable to those that were welded by traditional resistance welding. It is also found that LSS is changed with welding pressure of joint parts. Also, in order to elucidate the mechanism of self-resistance welding, the temperature of specimen and the current during welding process were measured. As a result, it was found that the process of self-resistance welding could be divided in two stages.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Vacuum assisted Resin Transfer Molding (VaRTM) is widely used for molding of composite structures. This paper presents a method to observe resin impregnation in a VaRTM process without embedding sensors into composite structures. The resin flow is estimated by an approach integrating a stochastic simulation of a VaRTM process with values of electrical capacitance measured between pairs of electrodes on a molding tool. This method is based on the ensemble Kalman filter (EnKF), known as a sequential data assimilation technique. The proposed method was examined by a numerical experiment and it was confirmed that the resin flow front could be estimated.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The Electrical Resistance Change Method (ERCM) is useful for CFRP (Carbon Fiber Reinforced Plastic) structures, because electrical conductivity of carbon fiber can be used as a sensor for damage detections. Fatigue damages need to be detected using the ERCM because these damages decrease the reliability of CFRP structures. This study experimentally deals with cyclic loading tests of CFRP laminates using ERCM. Moreover, the mechanism of electrical resistance change was investigated. First, the electrical resistance change was measured by four-probe method in the case of CFRP laminates with stacking sequence of [0/±45/90]s and [0_2/90_2]s- As a result, the electrical resistance of CFRP laminates with stacking sequence of [0/±45/90]s decreased with the increase of number of cycle. On the other hand, the electrical resistance of CFRP laminates with stacking sequence of [0_2/90_2]s increased with the increase of number of cycle. The mechanism of decreasing of the electrical resistance which can not be explained by the conventional thinking is due to the improvement of fiber fiber contact. Moreover, it is revealed that the improvement of fiber-fiber contact is caused by residual strain of ±45° ply.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The stress intensity factor is a fracture mechanics parameter that describes the stress field around a crack tip. When the stress intensity factor is used as a fracture mechanics parameter, the small-scale yielding condition in which the plastic-zone size near the crack tip should be sufficiently small relative to the crack length must be satisfied. When a steep residual stress distribution exists near a crack tip, the potential exists to deviate from the conditions, even for conditions that are satisfied by traditional criteria In this study, various shapes of residual stress distributions along the crack propagation path are considered in the crack propagation model based on the Dugdale model. The features of the residual stress distribution shape which influence the scale of yielding are investigated by conducting numerical analysis considering plastic-zone size fluctuation. Additionally, a simplified practical criteria to evaluate the condition is proposed when a steep residual stress distribution is present and the effectiveness of the criteria was discussed.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

When pressure test is conducted for impacted composite overwrapped pressure vessels (COPV) with locally deformed metallic liner, bending load is caused in the metallic liner at the deformed point When the repeated pressure test is conducted for the impacted COPV, cyclic alternating load is subjected to the deformed area When large alternating load is subjected to the area repeatedly, there is a possibility to cause ratchetting deformation, and eventually to cause fracture of the metallic liner The aim of this study is to observe deformed metallic liner behavior and to investigate stress condition of the deformed area during repeated pressure test The COPVs (111 5mm in diameter and 329mm in length) made of CFRP and aluminum liner were prepared for this study Impact load of 20J was subjected to the COPVs and pressure test of 20MPa in pressure were performed The shape of metallic liner at the impacted point was observed by using micro CT scan before and after pressure test Stress conditions of the liner during pressure test were also investigated by finite element analysis Ratchetting deformation couldn't observed directly in this study, although, repeated stress amplitude at the deformed area became larger than that at the sound area was founded by FEM analysis This result shows the possibility to cause ratchetting deformation when the metallic liner deformed locally by impact load

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

This paper discusses optimum design of a stiffened composite panel, which is used in aerospace structures. Anisotropic thermal expansion coefficients of the composite laminates causes complicated deformation of the panel after the curing. In previous researches, stacking sequence optimizations were performed without considering thermal deformation: a response surface was used to obtain an objective function, and lamination parameters were sued as variables for the response surface of the objective function such as buckling load. However, the thermal deformation must be considered as a constraint factor for actual composite structures. In the present study, therefore, thermal deformation is dealt with as a constraint for a stacking sequence optimization problem. Three surrogate models of the thermal deformation are discussed here: a conventional method using lamination parameters; a new method using thermal coefficients; a modified new method As a result, the modified new method is shown to be effective for the surrogate model.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Impact loads initiate damages of several forms such as an indentation, fiber breakage, matrix cracking, and delamination cracking in carbon fiber reinforced polymer (CFRP). In this study, rapid diagnosis, which can finish inspecting the whole aircraft structure within an hour during refueling, was developed for composite aircraft. The proposed method consists of two steps; the first target for detection is indentation in the whole structure, and the second one is delamination cracking. After an indentation is detected in the first step, you only have to inspect limited area around the indentation for delamination inspection. Therefore, you can make use of an indentation as a marker of impact damage and can save inspection time and money even if large CFRP components are inspected. In the first step for indentation detection, indentation increases fiber-fiber contact at the interlaminar interface and electrical conductivity. Consequently, electrical current applied to the material will concentrate around the indentation, and lead to selective and intense resistive heating. This temperature increase can be observed by thermography or detected as a change in electrical resistance caused by the temperature difference. In the second step, delamination around an indentation can be detected without sampling the data from intact structures using statistical treatment. Moreover false diagnoses from changes in resistance caused by damage to the electrical contacts at the electrodes can be prevented.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

An impact load on a thick carbon fiber reinforced plastic (CFRP) plate usually causes a dent. The dent results in a decrease of electrical resistance in the thickness direction. Our previous papers demonstrated the effect of the dent in the measurement of electrical resistance change of a thick CFRP plate subjected to impact loading. The present paper focuses on the mechanism of decrease of the electrical resistance caused by a dent. Experiments were performed to measure local fiber volume fraction after various loading. The observation revealed that the dent is made by plastic deformation of the matrix under compression loading at an impactor. This deformation cause slight increase of fiber volume fraction. The slight increase of the fiber volume fraction causes significant increase of electric conductance in the thickness direction.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In order to improve interfacial properties of an adherend of the bonded composites joints, in-mold surface preparation using imprint lithography is proposed. In the proposed method, microstructures are fabricated on the surface of the mold for forming composite materials. By forming composites on the mold, the shape of microstructures is transferred to the CFRP surface. In this method, since molding of composites and surface preparation can be conducted at once, it reduces the time required and costs involved in conventional surface preparation such as sand blasting, chemical etching etc In this paper, micro concavo-convex structures are fabricated on the surface of CFRP by in-mold surface preparation to improve the apparent mode I fracture toughness of CFRP/adhesive interface According to DCB tests, it was confirmed that the fracture toughness became stronger and fracture mode changed from interfacial failure to cohesive failure of adhesive as the aspect ratio A of microstructures increased.

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CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

During Resin transfer molding (RTM) process for manufacturing composites, entrapped air may remain as void in a part to bring significant decrease of the mechanical properties. In the past, it has presented that amount of the void formation depends on velocity of resin flow. However, in the case that an anisotropic fabric is applied, directions of the resin flow may also affect on the void formation. In this paper, the effect of anisotropy of fiber on void generation was examined analytically and experimentally. Finally, good agreement was obtained between results of them.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CFRP laminated structures are applied to many aerospace structures. Although the CFRP laminates have high specific strength and specific stiffness, delamination cracks are easily created and the delamination cracks are usually difficult to be detected by visual inspections. Recently, high toughness CFRP laminates are adopted to primary structures. The tough CFRP yields small fiber breakages when delamination crack is made in many cases. This requires a detection system of fiber breakages at low cost for large laminated CFRP structures. In the present study, TDR method is adopted. TDR method uses an electrical pulse wave and observes the reflected wave. The method is applied to a 2m CFRP strip specimen and notches are detected from the reflected pulse wave. Besides, the pulse wave propagated along CFRP strip specimen is investigated by the electromagnetic simulation using FDTD method.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, a new welding method which utilizes conductivity of CFRTP (Carbon fiber reinforced thermoplastic) is proposed. Electrical current is applied through the CFRTP single-lap joints in thickness direction. Since resistance of joining surface is the highest in the current path, the joining surface is preferentially heated by Joule heating. In this study, spot welding and surface welding were conducted. By applying constant voltage of 5.0V or ,10.3V, the joint-surfaces were heated above glass transition temperature of the material and were welded. In order to evaluate lap-shear strength (LSS) of welded joints by proposed method, tensile lap-shear tests were conducted. As a result, the tensile lap-shear true stress of spot welding is 31.0MPa and nominal stress of surface welding is 22.0MPa (CF Fabric/PEI) and 21.6MPa (CF Fabric/PPS) . These strengths were comparable to those that were welded by traditional resistance welding (19-22MPa) . It is also found that LSS is changed with welding pressure of joint parts.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Carbon Fiber Reinforced Plastic (CFRP) laminates are weak in durability against impact load, and it yields internal damage like delamination cracks. The electrical resistance change method (ERCM) is useful for CFRP structures, because electrical conductivity of carbon fiber can be used as a sensor for damage detections. Many researchers detect various kinds of damage of CFRP laminates by using the ERCM. However, the method has unsolved issues such as an effect of temperature change and an effect of cyclically loading in service. This study experimentally deals with the effects on the ERCM. At first it was revealed that the relationship between temperature and electrical resistance change was almost linear. This means that temperature compensation for temperature distribution is possible using the linear relationship. Moreover, it was investigated that the temperature coefficient depends on a fatigue of CFRP. Finally, temperature change was observed in fatigue tests, therefore electrical resistance is formulated as constant temperature. As a result, the electrical resistance decreases with the increase of number of cycles.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Vacuum assisted Resin Transfer Molding (VaRTM) is a composite molding process by which resin is drawn through fiber preforms using a vacuum pressure. We proposed a method to measure three-dimensional resin impregnation in a VaRTM process on the basis of the ensemble Kalman filter (EnKF). In this method, the resin-impregnated region was estimated by a combination of measuring capacitances from a set of electrodes and a simulation of a VaRTM process. The proposed method was examined by numerical experiments and it was confirmed that the flow velocity reduction in a low permeability region can be estimated.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Laminated Carbon Fiber Reinforced Polymer (CFRP) composites easily have delamination cracks resulting from small impact loads such as from dropped tools. Since the delamination cracks are usually difficult to detect by visual inspection, the CFRP laminates must have high knockdown capabilities to confirm their structural integrity. The present paper investigates Electrical Resistance Change Method (ERCM) for thick CFRP laminates. Authors have proposed the damage identification method for CFRP using the ERCM and confirmed its applicability for beams and thin plate-type specimens in the previous study. However, a dent is made for thick CFRP when an impact load is applied, and the dent causes electrical resistance decreases because the dent causes decreases of the thickness. The present study focuses on the electrical resistance decrease by the dent, and the electrical resistance decrease is used for monitoring delamination location. FEM analyses are used to obtain electrical resistance change decrease distributions. The estimation results are compared with the experimental data. 55 cases of FEM analyses were performed here to obtain the relationship between the damage and the electrical resistance changes. Using these results, response surfaces are made to obtain relationship between the fraction of electrical resistance change and delamination location. Experimental data are input into the obtained response surface and delamination locations are estimated. Several experimental data are input into the response surface and the estimations of delamination locations are made. As a result, the response surface made from the FEM analyses predicted successfully the damage location for the thick CFRP laminates.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In order to improve interfacial properties of an adherend of the bonded composites joints, in-mold surface preparation using nanoimprint lithography is proposed. In the proposed method, microstructures are fabricated on the surface of the mold used during curing process of composites. By forming CFRP on the mold with microstructures, the shape of microstructures is transferred to the CFRP surface. In this method, since molding of CFRP and surface preparation can be conducted at once, it reduces the time required and costs involved in conventional surface preparation such as sand blasting, chemical etching etc. In this paper, micro concavo-convex structure was proposed to improve the mode I fracture toughness of CFRP/adhesive interface and fabricated on the surface of CFRP by in-mold surface preparation. According to DCB tests, it was confirmed that the fracture toughness become stronger as the aspect ratio A of microstructures increased.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Comprehensive knowledge of the low-cycle fatigue properties of nuclear component materials, and nondestructive testing (NDT) techniques for fatigue damage detection are important when evaluating nuclear components affected by earthquakes. Acoustic emission (AE) testing can be used for the condition monitoring of the components. Therefore, we conducted low-cycle fatigue tests of austenitic stainless steel with AE monitoring. The results of fatigue tests showed that the estimation based on the usage factor (UF) could be useful for the life prediction. The results of AE monitoring also showed that the timing of AE generation changed by the remaining fatigue life, so the potential for characterization of fatigue damage was demonstrated by focusing timing of AE generation. Furthermore, the possibility of applying AE monitoring to NDT techniques was demonstrated through the results of these fatigue tests.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

If it is possible to inspect composite aircraft automatically and quickly after every flight, we can reduce the safety factor and allow for more flights. Although, an electrical resistance change method (ERCM) has been proposed as a self-monitoring method which can inspect rapidly even a large structure without expensive equipments, there are many problems with its practical application. In this study, a new diagnostic method, impact-damage visualization, was developed. Indentation damage increases fiber庸iber contact at the interlaminar interface and electrical conductivity. Consequently, electrical current applied to the material will concentrate around the damaged area, and lead to selective and intense resistive heating. This temperature increase can be observed by thermography or detected as a change in electrical resistance caused by the temperature difference. The lightning protection system of a composite aircraft was used to apply a uniform electrical current distribution and electric heat to a large structure. Subsequent coupled thermal-electrical analyses showed that even small indentations (depth <0.15 mm) could be relatively easily detected in structures >1 m in size.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

This paper discusses optimum design of a stiffened composite panel: the panel is widely used for weight reduction in aerospace structures. Anisotropic thermal expansion coefficients of the composite laminates causes complicated deformation of the panel after the curing. . In previous researches of the stacking sequence optimizations, the optimizations were performed without considering thermal deformation: a response surface was used to obtain an objective function at low computational cost, and lamination parameters were sued as variables for the response surface of the objective function such as buckling load ratio. However, the thermal deformation caused by the temperature change after curing must be considered as a constraint factor for actual composite structures. In the present study, therefore, thermal deformation is dealt with as a constraint for a stacking sequence optimization problem. Three surrogate models of the thermal deformation are discussed here: a conventional method using lamination parameters; a new method using lamination parameters and thermal coefficients; a modified new method As a result, the modified new method is shown to be effective for the surrogate model.

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Carbon Fiber Reinforced Plastic (CFRP) laminates are weak in durability against impact load, and it yields internal damage like delamination. The electrical resistance change method (ERCM) which is one of the nondestructive inspection is useful for CFRP structures, because electrical conductivity of carbon fiber can be used as a sensor for damage detection. Many researchers detect various kinds of damage of CFRP laminates by the ERCM. However, there are some effects such as a temperature change and a cyclically loading in real environment. This study experimentally deals with the effect on the ERCM. At first it was revealed that the relationship between temperature and electrical resistance change was almost linear. Moreover, it was investigated that the temperature coefficient depends on a fiber orientation angle. Finally, temperature change was observed in fatigue tests, therefore electrical resistance is formulated as constant temperature.

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

If it is possible to inspect composite aircraft automatically and quickly after every flight, we can reduce the safety factor and allow for more flights. Although, an electrical resistance change method (ERCM) has been proposed as a self-monitoring method which can inspect rapidly even a large structure without expensive equipments, there are many problems with its practical application. In this study, a new diagnostic method, impact-damage visualization, was developed. Indentation damage increases fiber-fiber contact at the interlaminar interface and electrical conductivity. Consequently, electrical current applied to the material will concentrate around the damaged area, and lead to selective and intense resistive heating. This temperature increase can be observed by thermography or detected as a change in electrical resistance caused by the temperature difference. The lightning protection system of a composite aircraft was used to apply a uniform electrical current distribution and electric heat to a large structure. Subsequent coupled thermal-electrical analyses showed that even small indentations (depth <0.15 mm) could be relatively easily detected in structures >1 m in size.

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The present paper investigates Electrical Resistance Change Method (ERCM) for thick CFRP laminates with a dent. The authors have proposed the damage identification method for CFRP using the ERCM and confirmed its applicability for beams and thin plate-type specimens in the previous studies. However, the dent is made for thick CFRP and the dent causes electrical resistance decreases. In the present study, we focus on the dent and the electrical resistance decrease is adopted for monitoring delamination location. FEM analyses are used to obtain electrical resistance decrease distributions. Response surfaces are adopted to estimate the delamination location here. The results show good agreements with the experimental data.

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In order to improve interfacial properties of bonded composites joints, in-mold surface preparation using nanoimprint lithography is proposed. In this method, CFRP is formed on the mold with microstructures and the shape of microstructures is transferred to the CFRP surface, which gives us adherent surface without any conventional surface treatment. In this paper, microstructures which improve mode I fracture toughness of adhesive joints were proposed and fabricated on CFRP laminates. It was confirmed experimentally that fracture toughness become stronger as the aspect ratio of microstructures increased.

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Comprehensive knowledge of the low-cycle fatigue properties of nuclear component materials, and nondestructive testing (NDT) techniques for fatigue damage detection are important when evaluating nuclear components affected by earthquakes. Acoustic emission (AE) testing can be used for the condition monitoring of the components. Therefore, we conducted low-cycle fatigue tests of austenitic stainless steel with AE monitoring. The results of fatigue tests showed that the estimation based on the usage factor (UF) could be useful for the life prediction. The results of AE monitoring also showed that the timing of AE generation changed by the remaining fatigue life, so the potential for characterization of fatigue damage was demonstrated by focusing timing of AE generation. Furthermore, the possibility of applying AE monitoring to NDT techniques was demonstrated through the results of these fatigue tests.

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CFRP laminated structures are applied to many aerospace structures. Although the CFRP laminates have high specific strength and specific stiffness, delamination cracks are easily created and the delamination cracks are usually difficult to be detected by visual inspections. Recently, high toughness CFRP laminates are adopted to primary structures. The tough CFRP yields small fiber breakages when delamination crack is made in many cases. This requires a detection system of fiber breakages at low cost for large laminated CFRP structures. In the present study, TDR method is adopted. TDR method uses an electrical pulse wave and observes the reflected wave. The method is applied to a 2m CFRP strip specimen and notches are detected from the reflected pulse wave. Besides, the propagation of the pulse wave is investigated by the electromagnetic simulation using FDTD method.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Vacuum assisted Resin Transfer Molding (VaRTM) is a composite molding process by which resin is drawn through fiber preforms using a vacuum pressure. We proposed a method to measure resin impregnation in a VaRTM process non-intrusively on the basis of the ensemble Kalman filter (EnKF). In this method, the resin-impregnated region was estimated by a combination of measuring capacitances from a set of electrodes and a simulation of a VaRTM process. The proposed method was examined by a numerical experiment and it was confirmed that the flow velocity reduction in a low permeability region can be estimated.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

From a traffic safety point of view, there is an urgent need for intelligent tires which can optimize braking control by estimating the slip ratio and friction coefficient between road surface and tire. This study develops a concurrent method for estimating the frictional and vertical loads applied to the tires from the measured strain data when both loads change. The method decomposes the measured circumferential strain to the frictional and vertical strain components using their symmetrical and anti-symmetrical characteristics. FEM analysis is used for simulating tire deformation under various wheel loads and braking torques. When the estimated and true applied loads were compared, it was confirmed that the vertical and frictional loads can be estimated independently from the circumferential strain with sufficient accuracy.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

This paper discusses optimum design of a stiffened composite panel: the panel is widely used for weight reduction in aerospace structures. Anisotropic thermal expansion coefficients of the composite laminates causes complicated deformation of the panel after the curing.. In previous researches of the stacking sequence optimizations, the optimizations were performed without considering thermal deformation: a response surface was used to obtain an objective function at low computational cost, and lamination parameters were sued as variables for the response surface of the objective function such as buckling load ratio. However, the thermal deformation caused by the temperature change after curing must be considered as a constraint factor for actual composite structures. In the present study, therefore, thermal deformation is dealt with as a constraint for a stacking sequence optimization problem. Three surrogate models of the thermal deformation are discussed here: a conventional method using lamination parameters; a new method using lamination parameters and thermal coefficients; a modified new method As a result, the modified new method is shown to be effective for the surrogate model.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

During Resin transfer molding (RTM) of composites, entrapped air in resin during resin impregnation may remain as voids in the product and depresses the mechanical properties. In this paper, bundle scale void formation in anisotropic plane woven fabric is focused. The effect of anisotropy on void formation is described by simplified model of void formation. Experiments were carried for the validation and good agreement was obtained between the result and the expectation of the analysis model.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CFRTP (Carbon fiber reinforced thermoplastic) has the superior properties such as high toughness, high productivity, recycling efficiency and repairability when compared with CFRP (Carbon fiber reinforced plastic). Another advantage of CFRTP is its weldability. Although several welding methods, such as resistance welding, ultrasonic welding and induction welding have been proposed, a new welding method which using electrical resistance of material itself is proposed in the study. In other words, electric current is loaded on through-thickness direction of single lap joint, and resin of welding area is melting. In this method, electric resistance of joint part is peak in the current pathway, welding area can be preferentially heated up. In this study, spot welding and surface welding were conducted. Tensile lap-shear tests were conducted for CFRTP joints welded by the proposed method. As a result, the tensile lap-shear strength (LSS) of spot welding is 31.0MPa and LSS of surface welding is 22.0MPa. Also, LSS is changed with welding pressure of joint parts.

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Language：Japanese   Publisher：日本工業出版  

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This study examined the applicability of acoustic emission (AE) method for the impact damage evaluation of CFRP pressure vessels. As a fundamental study, the characteristic features of AE signals obtained from impact-damaged CFRP laminates during tensile tests were analysed. Coupon-level CFRP specimens were prepared and impact forces were applied to the edge of the specimens so that the internal damages (e.g. delamination) could be observed from the edge-surface of the specimens. AE signals were detected via AE sensors mounted on the specimen surface during tensile loading test. For damaged specimen, it is found that the growth of delamination and the friction of delamination surfaces are the main AE sources. Also it is revealed that a large number of AE signals were detected during unloading period only for damaged specimens. These results showed a possibility that the AE method could be used for the impact damage evaluation of CFRP structures, including pressure vessels.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To increase the strength of CFRP bolted joints, we have tried to gain ffiction force between CFRP members by increasing a friction coefficient and a bolt-fastening force. In this study, the joint strength and the failure behavior of conventional and proposed joint were examined by finite element method analyses with degradation rules of material properties. The results show that the joint strength of the proposed joint was higher than that of conventional joint and the failure behavior was different from that of the conventional joint. To investigate the strength and the failure behavior of the actual proposed joint, the single-lap joint tensile tests with AE monitoring were conducted. The failure strengths of CFRP bolted joints with high-friction sheets and cone washers were higher than those of conventional CFRP bolted joints, and the failure behavior of the proposed joint was different from that of the conventional joint just like the finite element method analyses.

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Carbon Fiber Reinforced Polymer (CFRP) laminated structures are applied to many aerospace structures. Although the CFRP laminates have high specific strength and specific stiffness, delamination cracks are easily created and the delamination cracks are usually difficult to be detected by visual inspections. Recently, high toughness CFRP laminates are adopted to primary structures. The tough CFRP yields small fiber breakages hen delamination crack is made in many cases. This requires a detection system of fiber breakages at low cost for large structures. In the present study, Time Domain Reflectometry (TDR) is adopted. TDR uses an electrical pulse wave and observes the reflected wavefrom. The method is applied to a 2m CFRP strip specimen and notches are detected from the reflected pulse wavefonn.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The present paper investigates Electrical Resistance Change Method (ERCM) for thick CFRP laminates with a dent The authors have proposed the damage identification method for CFRP using thc ERCM and confirmed its applicability for beams and thin plate-type specimens in the previous studies. However, the dent is made for thick CFRP and the dent causes electrical resistance decreases. In the present study, we focus on the dent and the electrical resistance decrease is adopted for monitoring delamination location. FEM analyses are used to obtain electrical resistance decrease distributions. Response surfaces are adopted to estimate the delamination location here. The results show good agreements with the experimental data.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The current work investigates full-field monitoring of resin flow during a VaRTM using an area-sensor array. The squared area sensors are aligned as a matrix on a thin polyimide film without any un-sensing space; thus the film measures the full-field flow monitoring, and never misses a diy spot that may occur anywhere on the film. To identify the precise flow front and diy spots, the impregnated area is estimated by minimizing the residual sum of squares between the measured and estimated impregnated area ratios. Using the different characteristics of electrical properties, the electrical capacitance and resistance in case of out-of-plane and in-plane impregnation, the resin flow direction and distribution is estimated. In this study, we assume the RTM manufacturing of unsaturated polyester resin/glass fiber composites. These GFRP composites has vely different permittivity and resistivity characteristics between impregnated and un-impregnated states.

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In the previous study, unsupervised detection of delamination cracks in CFRP plates using statistical analysis of temperature characteristic of resistance were developed to prevent electrical resistance changes caused by damages of electrical contact at electrodes. Delamination cracks change temperature characteristic of resistance of CFRP laminates. To detect delaminations without learning processes, electrical resistances of multiple segments of a CFRP laminate at high temperature are compared with those at low temperature and a statistical analysis method discriminates the change. Electrical resistance changes caused by damages of electrical contact at electrodes do not affect the temperature characteristic of resistance. This method has applicability to existing structures and can also detect initial defects. As a result of the previous study, delamination at least 5.3 mm in diameter subjected to a quasi-static load in a quasi-isotropic-plied CFRP plate was detectable without intact data. The diagnosis was not affected by damages of electrical contact at electrodes except for perforated lack of an electrode. The present study employs the unsupervised detection method of delamination cracks and damages of electrical contact at an electrode subjected to falling weight impact loads, and dents subjected to quasi-static loads.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In order to improve interfacial properties of adhesively bonded composites, surface modification using Nanoimprint lithography (NIL) is investigated. Since the interfacial propeilies such as bonded strength or fracture toughness are highly depend on a surface morphology, these properties can be improved by designing and fabricating microstntures appropriately in the interface. Considering this fact we introduced NIL technique to the curing process of composites and fabricated microstnictures on the surface of composites, witich gives us stiff interface without any surface preparation such as sand blasting or chemical etching. We simulated the behavior of crack propagation along the interface with Finite element method using cohesive zone model and estimated model apparent fracture toughness of adhesive joints.

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It is important to expand knowledge for low-cycle fatigue properties of pre-strained nuclear component materials and nondestructive inspection (NDI) techniques for fatigue damage detection when considering resumption of nuclear power plant subjected veiy large load which caused plastic deformation, such as seismic load. As acoustic emission (AE) monitoring can be applied during fatigue test and operation of plants, we conducted AE monitoring during low-cycle fatigue test of austenitic stainless steel. The AE monitoring results showed that reduction of fatigue life by applied high pre-strain was caused by shorten of fatigue crack initiation life. The result also showed that the possibility to use AE monitoring for fatigue damage detection of nuclear power plants.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Surface modification by nanoimprint lithography (NIL) is applied to an adherend of the bonded composite joints. We developed a silicon mold with micro scale structures by photolithography and anisotropic etching. By fomiing CFRP on the mold with microstructures, the microstructures are transferred to the CFRP surface. Since this surface modification can be conducted during the curing of composites, it reduces the time required and costs involved in conventional surface preparation such as sand blasting, chemical etching etc. In this paper, the effect of microstructure size on the mode I fracture toughness was investigated. A size ratio A was defined and theoretical model to predict an effect of microstructure was proposed. Furthermore, DCB tests about some values of A were conducted. As a result, it was confirmed that as A increased, fracture toughness became stronger, and that theoretical model proposed gives a good approximation.

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From a traffic safety point of view, there is an urgent need for intelligent tires which can optimize braking control by estimating the slip ratio and friction coefficient between road surface and tire. In previous studies, we have proposed an application of strain data for estimating a friction coefficient. However, it only investigated the condition when the vertical or frictional loads changed but the other load remained constant. Since both of the frictional and vertical loads alter the measured strain data, an independent applied load estimation method is needed. This study develops a concurrent method for estimating the frictional and vertical loads applied to the tires from the measured strain data when both loads change. The method decomposes the measured circumferential strain to the frictional and vertical strain components using their symmetrical and anti-symmetrical characteristics. FEM analysis is used for simulating tire deformation under various wheel loads and braking torques and the relationship between the strain distribution at the sensing point and the applied loads are calculated. When the estimated and true applied loads were compared, it was confirmed that the vertical and frictional loads can be estimated independently from the circumferential strain with sufficient accuracy. Using this method, one can represent the slip slope curve during driving, which enables the optimization of vehicle control and implementation of a road condition warning system.

DOI： 10.1299/jmmp.4.1496

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Intelligent tires, also known as smart tires, are equipped with sensors to monitor the strain of the interior surface and the rolling radius of tire, and are expected to improve the reliability of tires and tire control systems such as anti-lock braking systems (ABS). However, the high stiffness of an attached sensor like a strain gauge causes sensors to debond from the tire rubber. In the present study, a novel optical method is used for the concurrent monitoring of in-plane strain and out-of-plane displacement (rolling radius) utilizing the non-planar surface of the monitoring object. The optical method enables noncontact measurement of strain distribution. The in-plane strain and out-of-plane displacement are calculated by using image processing with an image of the interior surface of a tire that is taken with a single CCD camera fixed on the wheel rim. This new monitoring system is applied to an aluminum beam and a commercially available radial tire. As a result, the monitoring system provides concurrent measurement of in-plane strain, out-of-plane displacement and tire pressure, and is shown to be an effective monitoring system for intelligent tires.

DOI： 10.1299/jmmp.4.520

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Language：English   Publisher：The Japan Scociety of Mechanical Engineers  

From a traffic safety point of view, there is an urgent need for intelligent tires which can optimize braking control by estimating the slip ratio and friction coefficient between road surface and tire. In previous studies, we have proposed an application of strain data for estimating a friction coefficient. However, it only investigated the condition when the vertical or frictional loads changed but the other load remained constant. Since both of the frictional and vertical loads alter the measured strain data, an independent applied load estimation method is needed. This study develops a concurrent method for estimating the frictional and vertical loads applied to the tires from the measured strain data when both loads change. The method decomposes the measured circumferential strain to the frictional and vertical strain components using their symmetrical and anti-symmetrical characteristics. FEM analysis is used for simulating tire deformation under various wheel loads and braking torques and the relationship between the strain distribution at the sensing point and the applied loads are calculated. When the estimated and true applied loads were compared, it was confirmed that the vertical and frictional loads can be estimated independently from the circumferential strain with sufficient accuracy. Using this method, one can represent the slip slope curve during driving, which enables the optimization of vehicle control and implementation of a road condition warning system.

DOI： 10.1299/jmmp.4.1496

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Language：English   Publisher：The Japan Scociety of Mechanical Engineers  

Intelligent tires, also known as smart tires, are equipped with sensors to monitor the strain of the interior surface and the rolling radius of tire, and are expected to improve the reliability of tires and tire control systems such as anti-lock braking systems (ABS). However, the high stiffness of an attached sensor like a strain gauge causes sensors to debond from the tire rubber. In the present study, a novel optical method is used for the concurrent monitoring of in-plane strain and out-of-plane displacement (rolling radius) utilizing the non-planar surface of the monitoring object. The optical method enables noncontact measurement of strain distribution. The in-plane strain and out-of-plane displacement are calculated by using image processing with an image of the interior surface of a tire that is taken with a single CCD camera fixed on the wheel rim. This new monitoring system is applied to an aluminum beam and a commercially available radial tire. As a result, the monitoring system provides concurrent measurement of in-plane strain, out-of-plane displacement and tire pressure, and is shown to be an effective monitoring system for intelligent tires.

DOI： 10.1299/jmmp.4.520

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In order to improve interfacial properties of adhesively bonded composites, surface modification using Nanoimprint lithography (NIL) is investigated. Since the interfacial properties such as bonded strength or fracture toughness are highly depend on a surface morphology, these properties can be improved by designing and fabricating microstructures appropriately in the interface. Considering this fact, we introduced NIL technique to the curing process of composites and fabricated microstructures on the surface of composites, which gives us stiff interface without any surface preparation such as sand blasting or chemical etching. We simulated the behavior of crack propagation along the interface with Finite element method using cohesive zone model and estimated mode I apparent fracture toughness of adhesive joints.

DOI： 10.1299/jsmemecjo.2010.8.0_3

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In the previous study, unsupervised detection of delamination cracks in CFRP plates using statistical analysis of temperature characteristic of resistance were developed to prevent electrical resistance changes caused by damages of electrical contact at electrodes. Delamination cracks change temperature characteristic of resistance of CFRP laminates. To detect delaminations without learning processes, electrical resistances of multiple segments of a CFRP laminate at high temperature are compared with those at low temperature and a statistical analysis method discriminates the change. Electrical resistance changes caused by damages of electrical contact at electrodes do not affect the temperature characteristic of resistance. This method has applicability to existing structures and can also detect initial defects. As a result of the previous study, delamination at least 5.3 mm in diameter subjected to a quasi-static load in a quasi-isotropic-plied CFRP plate was detectable without intact data. The diagnosis was not affected by damages of electrical contact at electrodes except for perforated lack of an electrode. The present study employs the unsupervised detection method of delamination cracks and damages of electrical contact at an electrode subjected to falling weight impact loads, and dents subjected to quasi-static loads.

DOI： 10.1299/jsmemecjo.2010.6.0_299

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The present paper investigates Electrical Resistance Change Method (ERCM) for thick CFRP laminates with a dent. The authors have proposed the damage identification method for CFRP using the ERCM and confirmed its applicability for beams and thin plate-type specimens in the previous studies. However, the dent is made for thick CFRP and the dent causes electrical resistance decreases. In the present study, we focus on the dent and the electrical resistance decrease is adopted for monitoring delamination location. FEM analyses are used to obtain electrical resistance decrease distributions. Response surfaces are adopted to estimate the delamination location here. The results show good agreements with the experimental data.

DOI： 10.1299/jsmemecjo.2010.6.0_297

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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For Caibon Fiber Reinforced Plastic (CFRP), electrical conductivity of caibon fiber can be used as a sensor for damage detection. The change of electrical resistance of the CFRP structure has been studied as a self-sensing system for monitoring damages. Todoroki et al. reported that the electrical resistance change meihod successfully monitored various damages like matrix cracking, fiber breakage and delamination in CFRP laminates. To apply the electrical resistance change method to practical structures, reliability of the electrodes is a key issue. This paper contains the proposal of "Lead-Wire Integrated Electrodes" and the investigation of the reliability of the proposed electrodes under cyclic load. The electrodes were bonded to CFRP surface by using copper plating after polishing of the specimen surface with sandpaper to remove the surface resin. Lead-Wire was put on the plating surface and bonded to the electrode by using copper plating, so the electrode and Lead-Wire were integrated. One of advantages of this proposed electrode is no initial defect Fatigue tests were carried out using a servo-hydraulic testing system. As a result, the electrodes had a fatigue life at the same level as the conventional strain gages under cyclic load.

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In recent years, a large number of CFRP members are used in aircrafts for weight saving. One of the major fastening methods for the CFRP members is bolted joint. CFRP bolted joints, although, have a problem that the cracks or plastic deformation are occurred at the bearing surface of CFRP members even by the tightening with low fastening force. As a result, CFRP failures around bolt holes occur by stress concentration, and strength of a CFRP joint becomes decreased. In order to improve this problem, configurations of the washers are changed in this study to relax stress concentration, and thin sheet with high friction coefficient is sandwiched between CFRP members to improve the friction force. In the validation testing, the failure strength of the proposal CFRP bolted joint become higher than normal CFRP bolted joints.

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This study examined the applicability of acoustic emission testing (AT) for the impact damage evaluation of CFRP pressure vessels. AE signals were detected during pressurization tests of CFRP pressure vessels. Five pressurization tests were performed to each of two vessels. After the third pressurization test, the impact test of 12-J or 15-J energy was conducted by using a drop-weight impact tester. As the pressurization test was repeated, the amount of AE hits became fewer before the impact test. After the impact test, however, the total AE hits increased temporarily. From these results, it is assumed that AT can be used for the impact damage evaluation of CFRP pressure vessels. In addition, there is some difference in the generating behavior of AE between two vessels. Since the impact energy differed with two vessels, a possibility that the grade of impact damage could be specified by AT was shown.

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In this research, surface modification using Nanoimprint lithography (NIL) is conducted to an adhesion area of the bonded joint. We developed a mold by photolithography and formed composites on the mold. Since this surface modification can be conducted within the curing time of composites, it reduces the processing cost and time, which was required for conventional surface preparation such as sand blasting or chemical etching. In this paper, experimental results of tensile test for the butt joint are reported. This paper also includes numerical analysis of the butt joint strength. We found out that pyramid-shape microstructures on the CFRP surface could improve the joint strength because peel stress was reduced by the slope of pyramid-shape microstructures.

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DOI： 10.1299/kikaia.75.266

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DOI： 10.1299/kikaia.75.266

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Fiber waviness is one of initial defects during processing such as filament winding. The fiber waviness causes reduction of compressive strength of the composite structure. The mechanism of growing of the fiber waviness is, however, not completely clear. In the present study, a new model of generating fiber waviness is proposed. It is assumed that the local fiber micro buckling causes the fiber waviness. The micro buckling is based on the compression load caused by shrinkage of a metal jig. Three processing faults are considered as causes of this micro buckling: bonding between a metal jig and a composite (poor release), insufficient cure of the resin (non-uniform temperature) and initial deflection of fibers (poor tension during FW process). The model predicts fiber micro buckling during cooling process after cure. In the present study, to simplify the experimental conditions, prepreg sheet is adopted instead of FW process and the fiber micro buckling predicted using the model is compared to the experimental results. As a result, the new model successfuly predicts the initiation of the fiber micro buckling during cooling process.

DOI： 10.1299/kikaia.75.243

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Language：Japanese   Publisher：The Institute of Electrical Installation Engineers of Japan  

DOI： 10.14936/ieiej.29.642

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Language：Japanese   Publisher：日本工業出版  

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高マンガン鋼レ-ル等の高減衰材料に対する超音波探傷のニ-ズが近年高まってきている.そこで本稿では低周波数の超音波の使用と高エネルギ超音波の送信によって高減衰材料への超音波探傷試験の適用を検討した.尚,高エネルギの超音波を送信するために本稿ではパルス圧縮技術を適用した.その結果,コイルによる感度調整を行うことが必要であるものの,高減衰材料に対する超音波の透過性という面で従来のスパイクパルスで超音波を励起する手法に比べて上記の手法が優れていることを示した.

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Language：Japanese   Publisher：日本実験力学会  

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Language：Japanese   Publisher：日本実験力学会  

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Authorship：Lead author,　Corresponding author   Language：English  

DOI： 10.1163/1568551053297094

Web of Science

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Language：English   Publisher：Acoustic Emission Working Group  

Troubles related to bolt relaxation and fatigue have occurred in many fields. In the automotive industry, plastic-region tightening method is recognized as a good technique for preventing the relaxation and fatigue of bolts. However, this method requires a special torque wrench and in volves a complicated procedure for stable tightening. Therefore, it is important that a new tight ening method and a wrench that simplifies plastic region bolt tightening are developed. Two types of tensile tests using a torque wrench and a tensile tester were conducted for two different strength bolts. The Mahalanobis distance (MD) technique was utilized for discriminating acoustic emission (AE) signals from noise signals. We found that we can monitor the yield point of a high strength bolt during loading by AE monitoring combined with the MD technique. Here, we con ducted a feasibility study for controlling plastic-region tightening by AE techniques.

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DOI： 10.1117/12.621558

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Authorship：Lead author,　Corresponding author   Language：English  

DOI： 10.4028/www.scientific.net/KEM.270-273.1898

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Language：Japanese   Publisher：日本実験力学会  

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Authorship：Lead author,　Corresponding author   Language：English   Publisher：Acoustic Emission Working Group  

In order to study the cryogenic properties of CFRP tank, we conducted pressurization test of a small filament-wound (FW) tank at cryogenic temperatures. We first investigated the orienta tion dependence of acoustic emission (AE) signals at both room temperature and LN2 tempera ture by using artificial source. Lamb-mode dispersive AE signals were monitored in the CFRP tank. In tests at room temperature, we used A0-mode Lamb waves for source location. However A0-mode Lamb waves at several angles were hardly observed at LN2 temperature. In this study S0-mode were used for source location. 60% of tank wall was damaged before this test, and many AE signals are generated from this damaged zone. We developed a new method to sepa rate AE signals generated at damaged zone utilizing signal duration. When the AEs from moni toring (or non-damaged) zone are evaluated, detail source location is possible using arrival time differences of AEs. Next we conducted pressurization test of the CFRP tank at LN2 temperature. About 660 AE events were visually extracted from detected 2800 AE hits. We then investigated the duration of AE events and 100 AE events are evaluated as AE generated at non-damaged zone. Source locations of 7 AE events are obtained from the area where leakage was identified by snoop test conducted after the pressurization test

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Language：Japanese   Publisher：The Japanese Society for Non-Destructive Inspection  

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DOI： 10.1117/12.434189

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We propose an AE source location method in a fiber-reinforced composite cylinder on the basis of guided waves. The composite has a complex lay-up; a fishing rod composed of glass fiber mat in the inner surface, 5 layers of unidirectional carbon fiber and a spiral carbon fiber in the outer surface. We first quantified the velocity dispersion of L(0,1) and F(1,1) mode cylinder waves using a pulse laser and an AE sensor. Artificial AE sources were next excited by a point YAG laser and detected by two sets of three AE sensors attached at 120o step on the surface. Waveform similarity and arrival time difference of F(1,1) mode at 225 kHz were utilized for locating the circumferential zone (split thrice into 120o zone) and axial zone (length direction in 7 mm step), respectively. Most artificial sources were identified into a correct zone. Utilizing the location algorithm developed, the initiation and progression of local damage during axial–compression of the rod were studied. The source locations estimated agreed with the location of fiber delamination revealed by post-test dye-penetrant examination

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Speackle interferometry is a wholefield non-contact metrology technique for measuring displacementt, otherwise shearography is one for strain measurement. In order to combine both techniques, we proposed a new system utilized two Michelson interferometers. Phase shifting technique is also used to obtain wholefield information. In this study, the author measures out-of-plane displacement and strain of point loaded aluminium disk and in-plane displacement and strain of tensioned bar with hole is also measured.

DOI： 10.1299/jsmezairiki.2001.0_141

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In order to measure 3-D surface deformation in the same site and situation simultaneously, a new optical set-up is constructed by combining Moire interferometry and Twyman-Green interferometry. Phase shifting techniques is applied to obtain 4 fringe image data for estimating u, v and w displacement separately. Furthermore, the phase connecting method using minimum spanning technique is applied to obtained rapping image data. Further improvement of image processing is needed for estimating accurate 3-D deformation.

DOI： 10.1299/jsmezairiki.2001.0_167

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