Three points bending tests were conducted on specimens of plain woven glass cloth/epoxy laminates (fiber volume fraction≈0.4) with notch and R curves were obtained. The effects of the thickness and the size of the specimens on the fracture toughness were investigated. The crack propagation was experimentally observed with the ink method. The electric potential method and the acoustic emission method were carried out to detect the initiation of the crack. In this study, the validity of these nondestructive inspection method was examined corresponding to the load-displacement curves.
The following results were obtained: (1) the effect of the thickness on the fracture toughness was less than that of the specimen size, (2) the outputs in the electric potential method were correlatable with the initiation of the damage and the propagation of macroscopic crack, and classified into three distinct patterns and (3) AE counts gave so much information for the fracture behavior in such a way that the initiation of the damage and the proportional limit corresponded to the initiation and the rapid increase of the AE event counts, respectively.
