The influence of notch on the acoustic emission generated during tensile testing of nuclear grade AISI type 304 stainless steel

Acoustic emission (AE) generated during tensile deformation of a nuclear grade AISI type 304 stainless steel with the presence of notches has been studied. Comparative analysis of AE activity from unnotched and notched specimens with varying notch lengths, as opposed to similar results reported in the literature for beryllium and aluminium alloys, has been made. It can be inferred from the present results that: (a) prior to and during yielding, higher acoustic activity is observed in notched specimens unlike those reported for beryllium and aluminium alloys and also the total AE counts increase with increase in the initial notch length, and (b) beyond yielding, acoustic activity of both the notched and unnotched specimens reduces. These observations have been explained by considering the increased localised deformation at the notch tip prior to and during yielding and by taking into account the phenomenon of blunting at the notch tip beyond yielding. An analysis of the total AE counts (N) with respect to the stress intensity factor (K) operative at the notch tip during macroyielding shows N to bear a relationship to K as N=AKm where A and m are constants. The value of m is found to lie between 1.11 and 1.93 unlike the reported value of m≥4 for aluminium alloys. The observed acoustic emission activity just before and during tearing of the notched specimens is also noted to be higher than that observed during necking elongation of unnotched specimens.