Effects of micro-structure on fatigue crack propagation and acoustic emission behaviors in a micro-alloyed steel

The effects of the change in micro-structures due to heat treatment and weld on fatigue and corresponding acoustic emission (AE) behaviors of Q345 steels were investigated. Four point bending fatigue tests were carried out, and AE monitoring was performed simultaneously. Based on the micro-structural characterization, mechanical properties studies, fractographic observations, and AE investigations, the AE source mechanisms and effects of micro-structure on AE during fatigue crack propagation were proposed. The results showed that the micro-structures, including the phase conditions, inclusions and precipitates, could significantly influence the fatigue crack propagation behaviors, thus influence AE source mechanisms and characteristics such as AE counts, counts rate, and AE transition phenomenon. By relating the AE signals to the micro-plastic and micro-fracture events, these effects of micro-structures were also reasonably explained in this study. These results suggest that the effects of micro-structures must be considered to obtain a more accurate estimation of fatigue damage through AE method.