DETERMINATION OF SURFACE RESIDUAL-STRESSES IN MACHINED CERAMICS USINGINDENTATION FRACTURE

Machining produces surface residual stresses which significantly influ ence the strength and wear resistance of ceramic components. As new me thods are da eloped for machining ceramics, a quick and reliable techn ique for measurement of residual stresses would be valuable in assessi ng the viability of these methods 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 measu red rising an indentation technique with a Vickers indenter In this te chnique, the surface extent of the median/radial cracks produced by th e Vickers indenter in machined and in annealed ceramics are measured. These are then combined with a fracture mechanics analysis to estimate the surface residual stresses produced by machining. In order to dete rmine the validity of the indentation technique for estimating machini ng residual stresses, these stresses were also measured using art X-ra y diffraction and a deflection method. The residual stress values dete rmined using the indentation technique in the machined ceramics were f ound to be reasonably close to those obtained from the X-ray diffracti on and deflection methods. Since the indentation technique is relative ly simple and easily applied it offers a promising method for evaluati ng surface residual stresses in machined ceramics.