RESIDUAL-STRESSES IN AL2O3-ZRO2 COMPOSITES - A TEST OF STOCHASTIC STRESS MODELS

In cooling sintered composites of Al2O3-ZrO2 from their fabrication te mperature residual stresses are created as a result of both the differ ence in thermal expansion between the two phases and the crystallograp hically anisotropic thermal expansion of the Al2O3 Phase. In this work the first and second moments of the residual stress distribution have been measured as a function of volume fraction of zirconia from 0.01 to 0.90. The measurement technique used is piezo-spectroscopy based on the optical fluorescence from Cr3+ dopants in the alumina phase. For zirconia volume fractions up to 0.35 the average stress accurately fit s the predictions given by the upper Hashin bound and this fit provide s a value of the average thermal strain in the composites. Using this value, the effective medium approximation produces an excellent descri ption of the average stress over the entire volume fraction. It is als o shown that the fluorescence broadening due to stress fluctuations li es close to the predicted upper and lower Hashin bounds modified by th e restrictions imposed by the principle of maximum entropy. The measur ed moments and those predicted by stochastic stress analysis compare w ell suggesting that the stochastic analysis provides a reliable method of calculating residual stress in composites.