Three dimensional analysis of thermal stress and prediction of failure of polytypoidally joined Si3N4-Al2O3 functionally graded material (FGM)

Abstract

Three-dimensional analysis methods to calculate residual stress for functionally graded material (FGM) sample using sialon polytypoids to join silicon nitride and Alumina are introduced in this paper. The various multilayered FGM samples with 3, 9, and 20 layers were sintered to fabricate a crack-free joining of heterogeneous ceramics. To calculate three-dimensional thermal stresses of those fabricated FGM samples, a finite element analysis tool, ALGOR, was used. The Von Mises failure criterion and the maximum stress criterion were applied to predict failures in the FGM samples. For each case, calculated strength of each FGM layer by rule of mixture was compared with predicted thermal residual stresses. The Von Mises failure criterion predicted the locations of cracks more precisely than the maximum stress criterion. Such analyses are especially useful for graded FGM samples where the residual stresses are very difficult to measure experimentally.