Behavior of Secondary AE Generation during Low-Cycle Fatigue Test of Austenitic Stainless Steel
Makoto OHTA, Yoshihiro MIZUTANI, Akira TODOROKI, Ryosuke MATSUZAKI and Tetsuo YASUOKA
Abstract:Acoustic emission (AE) testing is one of the major nondestructive testing (NDT) techniques, and it can be used as the real-time monitoring method for the purpose of detecting fatigue damages. However, AE testing data for steels during the low-cycle fatigue test is rarely reported. In this study, AE monitoring was conducted during low-cycle fatigue test for austenitic stainless steel with the aim of detecting fatigue damages and identifying the source of AE. A large number of AE were generated through the fatigue test and the AE data were divided into the increscent phase and decrescent phase. When focusing on the centroid frequency of AE, low frequency data had been observed since the crack size became detectable by PT. Those AE occurred in the process of increscent phase which is loading under tensile and unloading under compression and the contact of the crack surfaces were observed at the increscent phase. This means that the low frequency AE were secondary AE which were induced by friction of the crack surfaces. The behavior of crack surfaces was analyzed by FEM. The results showed that contact condition of crack surfaces were different between crack opening and closure, and it was revealed that friction-induced AE was mainly generated at the crack opening process. Therefore, the potential for monitoring low-cycle fatigue crack was demonstrated by focusing on both the friction-induced AE (secondary AE) and primary AE. Key Words:Low-cycle fatigue, Acoustic emission, Secondary AE, Stainless steel, Fatigue crack detection, Crack closure