Scratch deformation mechanism of copper based on acoustic emission

Due to significant localised deformation during the scratch process, the stress and strain states of the contact region are complex. The acoustic emission (AE) is defined as a transient elastic wave generated when strain energy is suddenly released due to the relative motion among the particles or materials at a small scale. Therefore, the AE signal is sensitive to the changes in stress and strain states during the scratch process. In this paper, the AE method was used to investigate the plastic deformation mechanism of copper (Cu), which is a typical ductile material, by a scratch test, using a diamond indenter to move across the surface of the Cu. Continuous AE signals were detected in the experiments and the fluctuation of the waveforms was attributed to the pile-up of dislocations. The results also illustrated that the AE intensity increased with increasing applied load, but had a complex relationship with the scratch velocity. For a low applied load, the AE intensity showed a corresponding increase as the scratch velocity increased, while for the high applied load, the AE intensity first increased and then decreased with increasing scratch velocity. The AE mechanism was discussed from the dislocation motion point of view, considering the stress, strain rate and temperature.