Effect of thickness of 90°-plies on a method for detection of matrix cracking of CFRP laminates is investigated here. Three types of cross-ply CFRP laminates are adopted here: 0/90/0_T, 0/90s and 0/90_2_T. Tensile cyclical loading tests are performed with increasing the maximum load applied cyclic loading. Electrical resistance changes are measured using silver paste electrodes by means of a four-probe method. As a result, it was revealed that residual electrical resistance under complete unloaded condition was not applicable for an indicator of creation of matrix cracking in the thick cross-ply laminates. For the thick cross-ply laminates, tensile residual stress in the middle 90°-plies is smaller than that of the thin laminates. This small tensile residual stress causes crack closure when the specimen is completely unloaded. When the cross-ply laminates are reloaded, the electrical resistance increased rapidly with the small increase of load due to the opening of matrix cracks. From this result, we proposed a new method for detections of matrix cracking using the rapid increase of electrical resistance in small reloading.
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