Acoustic emission technique for detecting micro- and macroyielding in solution-annealed AISI Type 316 austenitic stainless steel

The acoustic emission (AE) technique has been used to detect the microplastic yielding occurring during macroscopic elastic deformation in an AISI Type 316 stainless steel. It has been observed that selection of different resonant frequency sensors is essential to detect the AE signal with maximum sensitivity at different strain levels during tensile deformation. An attempt has been made to develop a theoretical model to predict the approximate frequency range of the AE signal generated from dislocation sources operating during pre-yield and near-yield tensile deformation. The frequency of the AE signal has been calculated from the event life time of the Frank-Read and grain boundary source operations. The model for predicting the frequency of the AE signal from Frank-Read source operation during pre-yield deformation has been verified by the experiments on a nuclear grade AISI Type 316 stainless steel. This model has also been extended to predict the frequency of the AE signal from the grain boundary source operation near the macro-yield region and its validity has been verified by considering the AE results obtained on aluminium, copper and AISI Type 316 stainless steel by different investigators. This study has shown good agreement between the theoretically estimated and experimentally observed values. This study has established a simple, but reasonably accurate model which could help in selecting the resonant sensors with suitable frequency for detecting both the microplastic yielding and macroyielding with high sensitivity during proof testing of pressure vessels and pipes and other components used in various industries.