Study on subsurface damage behavior in ductile ultra-precision grinding of sapphire based on acoustic emission signal processing

Chemical corrosion, photothermal absorption and acoustic emission were used to multidimensionally evaluate and monitor subsurface damage behavior in ductile ultra-precision grinding of sapphire. The optimum ductile grinding surface can be obtained at different grinding depths when grinding with constant-depth. The density of corrosion dislocation craters and the value of photothermal absorption increased with grinding depth, and the subsurface damage scales under the ductile grinding surface were distinct. Subsurface damage was dominated by cracks and spalling. Severe brittle fractures occurred at greater grinding depths in varied-depth grinding. The corroded grinding surface consisted of the original polishing surface, the ductile grinding surface, and the brittle fracture characteristic. The amplitude and fluctuation of grinding force increased with grinding depth. The original signal and Fourier transform cannot monitor the damage behavior. A signal processing model based on wavelet transform, signal reconstruction and fast Fourier transform was developed. The processed signal characteristics can correspond to the damage behavior under the ductile grinding surface.