Study of fatigue crack growth in RAFM steel using acoustic emission technique

Abstract

Acoustic emission technique (AET) has been used for characterization of fatigue crack growth (FCG) of a reduced activation ferritic-martensitic (RAFM) steel, a candidate structural material for the first wall and blanket applications in fusion reactors. The rate of AE activity generated as counts per cycle and energy per cycle has shown discontinuities corresponding to change in cyclic plasticity, crack closure and intergranular cracking in the transition regime. Peak amplitudes (PAs) of AE hits (events) could be used to distinguish crack growth in different regions of the FCG. The intergranular cracking in the transition regime is characterized by higher number of hits with peak amplitude up to 88dB along with the appearance of emissions with PA from 66 to 88dB. The variation of event duration with peak amplitude have shown that the FCG process is characterized by signals of two groups at higher values of ΔK whereas the closure and transition regimes are characterized by single group of signals.