Measurement of residual stresses in machined ceramics using the indentation technique

Machining produces surface residual stresses which significantly influence the strength and fatigue resistance of ceramic components. As new methods are developed for machining ceramics, a quick and reliable technique for measurement of residual stresses would be valuable in assessing the viability of the new machining method from a residual stress perspective. The residual stresses on ground and polished (i.e. machined) surfaces of soda-lime glass, Ni-Zn ferrite, and silicon nitride have been measured using an indentation technique with a Vickers indenter. In this technique, the surface extent of the median/radial cracks produced by the Vickers indenter in machined and in annealed ceramics are measured. These are then combined with a fracture mechanics model to estimate the surface residual stresses in the machined ceramics. In order to determine the validity of the indentation technique for estimating machining residual stresses, these stresses were also measured using an X-ray diffraction and a deflection method. The residual stress values determined using the indentation technique in the machined ceramics were found to be reasonably close to those obtained from the X-ray diffraction and deflection methods. Since it is relatively simple and easily applied, the indentation technique appears to be a potentially promising method for evaluating residual stresses in machined ceramics.