Papers by Author: Akira Todoroki

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Authors: Yoshinobu Shimamura, Keiko Oda, Akira Todoroki, Hideo Kobayashi, Takaomi Inada
Abstract: Bolted joints are widely used for composite structures. As is well known, excessive bearing load gives rise to bearing failure at hole boundaries. Detecting bearing failure is important for assuring integrity of composite structures. Conventional nondestructive inspection methods are expensive, cumbersome, time-consuming, and not suitable for health monitoring, and a simple, low-cost inspection method for bearing failure must be developed. Authors have experimentally demonstrated detection bearing failure by an electrical resistance change method. In this study, detectablity of remote damage, which includes bearing failure, using an electric resistance change method is investigated analytically. The results show that fiber breaking and delamination induce permanent increase in the electric resistance of the bolted composite joints, and that the proposed method, which involves measuring electric resistance, is effective for detecting bearing failure.
653
Authors: Masahito Ueda, Akira Todoroki
Abstract: CFRP laminate is sensitive to impacts. Even a low impact creates delamination, bringing deterioration of the structural reliability. Monitoring for delamination is, therefore, indispensable to maintain the reliability of a CFRP structure. In this study, asymmetrical dual charge electric potential change method was introduced to estimate a delamination in the CFRP laminate. Delaminations were estimated using response surfaces as solver of the inverse problem. Learning data of response surfaces were calculated by FEM analyses. Actual delaminations in the CFRP laminate were successfully identified.
1309
Authors: Akira Todoroki, Masahito Ueda, Yoshinobu Shimamura
Abstract: Electrical resistance change method has been applied to monitor a delamination crack of a thin CFRP laminate. For a thick CFRP laminate, multiple delamination cracks are made with many matrix cracks, and the electric current in the thick CFRP laminate may not flow in the thickness direction due to the strong orthotropic electrical conductivity. The present study employs an electric impedance change method for the identification of damage location and dimension of the damaged area; applicability of the method is investigated experimentally using thick beam-type specimens fabricated from cross-ply laminates of 36 plies. After making the damage, electrical impedance was decreased. A residual stress relief model was proposed to explain the decrease. From the measured electrical impedance changes, the relationships between the electrical impedance changes and damages are obtained by means of response surfaces. The response surfaces estimated the damage location and dimension of the damaged area exactly even for the thick CFRP laminates. The electrical impedance change method can be used as an appropriate sensor for measurement of residual stress relief due to damages of thick CFRP laminates.
1298
Authors: Yoshinobu Shimamura, Keiko Oda, Akira Todoroki, Masahito Ueda
Abstract: Bolted joints are widely used for composite structures. As is well known, excessive bearing load gives rise to bearing failure at hole boundaries. Detecting bearing failure is important for assuring integrity of composite structures. Since conventional nondestructive inspection methods are expensive, cumbersome, time-consuming, and not suitable for health monitoring, a simple, low-cost inspection method for bearing failure must be developed. Authors have demonstrated the feasibility of detecting bearing failure by using an electric resistance change method. In this study, more detailed analyses were carried out to investigate the detectability in terms of the damage size and the distance between damage and electrodes. The results show that bearing failure of less than 10mm square causes the electric resistance change of a few hundred ppm and thus can be easily detected, and that the electrodes can be mounted more than 10 mm far from a bolt hole.
957
Authors: Kazuomi Omagari, Akira Todoroki, Yoshinobu Shimamura, Hideo Kobayashi
2096
Authors: Takaomi Inada, Yoshinobu Shimamura, Akira Todoroki, Hideo Kobayashi
1852
Authors: Atsushi Iwasaki, Akira Todoroki, Satoshi Izumi, Shinsuke Sakai
Abstract: The present paper proposes a new diagnostic tool for the structural health monitoring that employs a Kriging Interpolation. Structural health monitoring is a noticeable technology for aged civil structures. Most of the structural health monitoring systems adopts parametric method based on modeling or non-parametric method such as artificial neural networks or response surfaces. The conventional methods require FEM modeling of structure or a regression model. This modeling needs judgment of human, and it requires much costs. The present method does not require the process of modeling, in order to identify the damage level using the discriminant analysis. This suggest us, this technique is applicable to the health monitoring system, which identifies the damage of the structure, easily. In the present paper, we developed the damage diagnostic methods using Kriging method for identifying delamination from data. Kriging method is a interpolation technique which shown in geostatistic. We applied this method to identifications of delamination crack of CFRP structure. Delamination cracks are invisible and cause decrease of compression strength of laminated composites. Therefore, health-monitoring system is required for CFRP laminates. The present study adopts an electric potential method for health monitoring of graphite/epoxy laminated composites. The electric potential method does not cause strength reduction and can be applied existing structures by low cost. As a result, it was shown that this method is effective for identification of damages.
1422
Authors: Akira Todoroki, Roysuke Matsuzaki, Yusuke Samejima, Yoshiyasu Hirano
Abstract: Authors’ group has been done researches on the damage monitoring of the laminated Carbon Fiber Reinforced Plastic (CFRP) using the electrical resistance change method. The method adopts reinforcement carbon fibers as sensors, and it is called self-sensing method. Using thin CFRP laminates, delamination crack location and dimension are identified with the electrical resistance change method. However, the electrical resistance decreases when a delamination crack is made in a thick CFRP beam. The present paper experimentally investigates the effect of the dent for the measurements of electrical resistance change. Indentation tests are performed for the thick CFRP plates. The effect of the dent is calculated compared with the effect of piezoresistivity caused by the residual stress relief. As a result, the effect of the dent is larger than the effect of the residual stress relief for the thick CFRP. For the thick CFRP, dents cause the significant reduction of the electrical resistance in the thickness direction, and that causes electrical resistance decrease.
963
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