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

• Acoustic emission (AE) study during fatigue crack growth test of RAFM steel
• Variation in AE rate vs ΔK shows discontinuities at different points.
• The discontinuities are attributed to change in cyclic plasticity, crack closure and intergranular cracking in the transition regime.
• Peak amplitudes of AE could be used to distinguish crack growth in different regimes of the FCG.
• The variation of event duration with peak amplitude also enable to distinguish crack growth in different regimes.

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 88 dB along with the appearance of emissions with PA from 66 to 88 dB. 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.