Abstract
In order to investigate fracture modes and timing for two types of CFRP plates during cryogenic shock testing, Acoustic Emission (AE) monitoring was conducted. No damage was observed for the specimen that made of heat-resistant matrix, however, thirty-nine matrix cracks were observed for the other specimen. Several cracks were observed even at the location where temperature differences on both surfaces were small. The AE signals were classified into three types by waveform characteristics according to the damage behavior. After that, three fracture modes of matrix crack, delamination and transverse cracks were simulated by pulse-laser irradiation to the CFRP plate and the detected AE signals were compared to estimate those obtained at cryogenic shock testing. The number of the AE signals linearly increased untill the LN2 disappeared from the cooling cell. Then, we conducted the vertical immersion test to examine the influence of cooling temperature to the damage occurrences. At temperatures lower than 228K, matrix cracks initiated at the specimen surface. At 213K, large number of AE signals due to matrix crack and few number of AE signals due to delamination and transverse crack were observed. At 77K, large number of AE signals caused by three types of fractures was detected.
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