Understanding the damage evolution of sapphire under scratching from AE signals

In this paper, the study on damage evolution of sapphire induced in scratching process using acoustic emission (AE) technology was carried out. Single-grit scratches with ramp scratch depth were conducted on C-plane of sapphire with AE signal monitoring. Groove microstructure after scratching shows that the damage evolution process is mainly determined by the interactions among cracks, specimen surface and groove boundary. To evaluate the damage evolution, the AE waveform indexes, i.e. fractal and frequency characteristics, were fully analyzed and correlated with groove microstructure of specimen after tests. It is found that the fractal dimension (FD) can identify the three basic damage modes as well as various damage behaviors during scratching process. In addition, the model of damage evolution is further proposed. The frequency characteristics of AE signals are distinctive to various damage behaviors during their evolution, especially to the occurrences of the critical damages and removal modes. Furthermore, the characteristic frequency band (CFB) of AE signals was extracted. It is found that FD of the reconstructed AE signals in CFB (86.8–161.4 KHz herein) can highlight damage details and features during initial damage stage of sapphire in scratch test effectively.