Acoustic emission mechanisms during high-cycle fatigue

Acoustic emission was obtained during fatigue crack propagation in a D6 tool steel and a 1015 mild steel using two different load ratios, R. It was found that the slope of the acoustic emission count rate vs stress intensity factor was higher when R = 0.2 than when R = 0.4. These results are described in terms of several models of acoustic emission mechanisms available in the literature as well as by a proposed new model. It is concluded that the observed R dependence can be explained by the combination of the contribution of two different models. These two models are the new plastic yielding as well as the crack tip fracture processes.