Fatigue Damage Evaluation of 2.25Cr-1Mo-0.25V Steel Using Acoustic Emission Entropy

Acoustic emission technique has become a promising and reliable tool for evaluating fatigue damage in engineering structures and materials. In this study, a new threshold-independent AE parameter, namely, entropy, was utilized for monitoring and evaluating the condition of fatigue damage in 2.25Cr-1Mo-0.25V steel during the fatigue crack growth process. The results showed that three fatigue damage stages were distinctly recognized by means of the variation of entropy with respect to fatigue loading time. Specifically, the first stage was related to fatigue crack initiation and small fatigue crack growth, and the second stage was associated with stable crack growth, whereas the final stage corresponded to unstable crack growth and final failure. Most importantly, the sudden rise of entropy could provide the warning sign at the critical damage point where the growing cracks propagated into the unstable growth phase. Additionally, fatigue damage mechanisms were correlated well with the generation of AE entropy by scanning electron microscope (SEM) analyses. Results from this work present a new strategy for evaluating fatigue crack growth in engineering materials and provide fundamental understanding on the fatigue mechanisms contributing to the generation of AE signals.