Damage evolution and rupture prediction of 42CrMoA nitrided steel by acoustic emission and infrared thermography techniques

The real-time monitoring and qualitative assessment of damage evolution of surface hardening materials is desirable, but still intractable, especially for quantitative evaluation. In this paper, the acoustic emission (AE) and lock-in infrared (IR) thermography techniques are used to assess the damage evolution of 42CrMoA nitrided steel. The acoustic and IR signals were experimentally obtained by the AE sensors and IR detector, respectively, with the sensors and detector distributed rationally during the fatigue test of sine amplitude loading. Based on the theory of discrete-time Fourier transform, fracture behaviours of nitrided steel are discriminated and confirmed by the fractograph. The results show that the formation of micro-crack, micro-void and dimple during the failure process are the sources of AE signal, and their influence effects are evaluated based on the energy of AE events that correspond to a certain frequency range. Also, the thermal dissipation behaviours of crack propagation are studied. The crack length is quantified based on the theory of grey level. The rupture time can be predicted by the burst AE or IR signals.