Acoustic emission was investigated during the fatigue, under constant plastic strain control, of single crystals which were oriented for easy glide. The results of acoustic emission analysis were compared with the cyclic response and hysteresis loop shape in various stages of fatigue. It was shown that acoustic emission techniques, using spectral analysis, were sensitive to all of the essential structural changes which occurred in dislocation ensembles during fatigue. These included matrix hardening, the formation of veins and channels, persistent slip band nucleation and crack initiation. It was shown that the maximum of the median frequency of the acoustic emission power-spectrum density in the intermediate stage of rapid hardening could be considered to be an indicator of local softening followed by strain localization in persistent slip bands. Crack nucleation was associated with a steep increase in the acoustic emission median frequency. A comparison was made of the acoustic emission behaviours during monotonic and cyclic testing, and the mechanisms of acoustic emission were explained in terms of the cooperative motion of dislocations.

Spectral Analysis of Acoustic Emission during Cyclic Deformation of Copper Single Crystals. A.Vinogradov, V.Patlan, S.Hashimoto: Philosophical Magazine A, 2001, 81[6], 1427-46