Spectral analysis of acoustic emission during cyclic deformation of copper single crystals

Abstract

Acoustic emission (AE) is investigated during fatigue at constant-plasticstrain control of copper single crystals oriented for easy glide, aiming at AE monitoring of structural transformation and dislocation self-organization during cyclic deformation. The results of AE analysis are compared with the cyclic response and hysteresis loop shape on different stages of fatigue. It is shown that the modern AE technique employing spectral analysis is sensitive to all essential structural changes in dislocation ensembles during fatigue such as matrix hardening, formation of veins and channels, persistent slip band (PSB) nucleation and development until crack initiation. The evidence is given for early identification of strain localization by means of AE. It is shown that the maximum of median frequency of the AE power spectral density at the intermediate stage of rapid hardening can be considered as an indicator of local softening followed by strain localization in PSBs. The moment of crack nucleation is identified by a steep increase in the AE median frequency. A comparison is made with the AE behaviour in monotonic and cyclic testing and the mechanisms of AE are discussed in terms of co-operative motion of dislocations.