Smart structures are appropriate approaches to obtain high reliability for structures made of CFRP. Electrical potential method for detection of damages does not bring strength reduction of CFRP structures. Authors have studied the effects of orthotropic electrical resistance on detection of delamination cracks, and have proposed a new approach for measurement of the electric resistance in the thickness direction by using FEM. In the present study, numerical analysis conducted in detail to investigate the effect of electrode positions on detection of delamination cracks by using the electric potential method. FEM analysis shows that construction of electrodes on 0°-ply surface is the best way to detect the delamination cracks from voltage changes between electrodes. Multiple cases of delamination size and position are calculated, and compared with each other. As a result, it is shown that the delamination cracks can be detected by using electric potential method, but the identification of the size and position of the delamination cracks is very difficult even if electric voltage changes are measured among 3 points. For the identification of the size and position, more information would be required.

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Although mechanical properties of carbon fiber reinforced carbon (C/C) composites under high temperature environment have nowadays been widly studied, the influence of thermal shock on C/ C composites have scarcely been investigated due to the lack of high-speed heating equipment. Ourequipment based on a high frequency induction heating method provided a solution. In the present study, we examined the influence of thermal shock on the interlaminar shearing strength (ILSS), which is one of the most important subjects of designing the plain woven C/C composites with a three point bending test. By the change of the span-to-height ratio (l/h), the failure mode shift of the interlaminar shearing to the bending was observed. By a series of tests, we proposed an appropriate l/h ratio to obtain a reliable interlaminar shearing strength of C/C composites, which would be higher than that for the conventional CFRPs. The observation of the fracture specimens was done by scanning electron microscopy (SEM) and optical microscopy. Not only 0°/90° inter-facial debonding but the expansion of transverse cracks were observed in the thermal shocked specimens. 0°/90° interfacial debondings were suggested to be the main source of the interlaminar shearing strength deterioration.

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