Evaluation of crack growth stage of sapphire under scratching based on AE signals

For hard-brittle materials, crack initiation and growth is an important factor to determine the surface quality of components during machining process. In this paper, the crack growth stage of sapphire was investigated based on acoustic emission (AE) signals through single-grit scratch experiments. The AE waveform indexes, i.e. fractal and frequency characteristics, were fully analyzed and correlated with groove microstructure of specimen after tests. The research shows that the specimen undergo four stages of crack growth successively as scratch depth increasing. It is found that the fractal dimension (FD) and frequency characteristics of AE signals are distinctive to various damage behaviors and be used to evaluate crack growth stage induced in machining process effectively. Especially, the FD distribution is sensitive to the occurrences of the critical damages and removal modes resulting from crack growth in scratch procedure. This paper can shed light on the control of surface integrity and subsurface damage of hard-brittle materials in ultra-precision manufacturing.