Photoacoustic thermoelastic effect near Vickers indentations in nanocrystalline nickel

The character of the photoacoustic (PA) signal variations in the vicinity of Vickers indentation zones in nanocrystalline nickel has been studied. PA images revealing the response signal features inside and outside these zones have been obtained. The character of the PA signal variation is compared to that predicted by the existing model relating the PA response to stress-induced changes in the thermoelastic coupling coefficient of the material. It is shown that the existing model adequately describes the observed character of internal stress variations near the indentations sites only in the absence of additional stresses related to the sample preparation technology.