Journal of the Japan Society for Composite Materials

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Moisture absorption affects mechanical properties of CFRP, thus monitoring of moisture absorption ration in CFRP is useful to assess the structural integrity. Besides, health monitoring of CFRP by using an electrical resistance change method has been investigated recently. In order to apply the electrical resistance change method to composite components in service, it is important to understand the effect of moisture absorption on the electrical resistance change. We have reported that the electrical impedance of CFRP increases not only in the transverse direction but also in the fiber. In order to investigate the effect of deformation constraint on the electrical impedance increase in the fiber direction, the electrical impedance changes of constrained and unconstrained CFRP specimens are measured at constant temperature and humidity. The results show that the electrical impedance change of the constrained specimen is much smaller than that of the unconstrained. The experimental results indicate that swelling in the transverse direction affects the electrical impedance in the fiber direction. The mechanism of electrical impedance change is discussed by using finite element analysis. The analytical results show that discrete contacts between carbon fibers and electrodes cause the electrical impedance change.

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As the first step for discussing the reliability of composite structures, a fundamental study is performed to obtain the scattering characteristics of glass-fiber reinforced plastics (GFRP) and woven carbon-fiber reinforced plastics (WCFRP) as well as reference metal. The bending stiffness of materials is evaluated by Euler bucking tests. The experiments are conducted for specified rectangular specimens with simply supported edges. A new attachment to realize the simply support boundary conditions for composite materials have been developed in these experiments. The scattering data in the results for GFRP and WCFRP composites were compared with those of a typical metal of aluminum alloy. The experimental data were compared with numerical simulations including the uncertainties of materials.

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