Monitoring for damage in two-dimensional pre-stress scratching of SiC ceramics

This paper reports an approach to use the acoustic emission (AE) technology for monitoring the surface/subsurface damage in twodimensional pre-stress scratching of SiC ceramics, in which the two-dimensional pre-stress is used to decrease the scratch-induced damage. Experiments in this study were conducted on a UMT-2 machine (CETR USA) utilizing a designed pre-stressing device under pressures of 0 MPa, 300 MPa and 500 MPa. The experimental results demonstrate that average frequency and magnitude of AE signals have a good correlation with the scratching tangential force and the scratch-induced surface /subsurface damage of materials. For a given normal load, the average frequency and magnitude of AE signals are observed to decrease with the increase in pre-stress, which indicates that surface/subsurface damage of SiC ceramics induced by two-dimensional pre-stress scratching is less than that induced by conventional scratching. The findings provide fundamental information for developing a practical on-line AE monitoring system that is effective in detecting surface/subsurface damage in scratching or grinding of ceramics. These results also demonstrate that two-dimensional pre-stress method contributes to decreasing the machining damage of brittle materials.