Finite element analysis of thermal residual stresses at graded ceramic-metal interfaces. Part I. Model description and geometrical effects

An elastic-plastic finite element method numerical model has been formulated to study residual stresses developed at graded ceramic-metal interfaces during cooling. The results were compared with those obtained for sharp (nongraded) interfaces to assess the potential for achieving residual stress reductions. Analyses were conducted for various axisymmetric cylindrical specimen geometries relevant to structural joining, coating, and thick film applications. The graded microstructure was treated as a series of perfectly bonded layers, each having slightly different properties. Constitutive relations for the interlayers were estimated using a modified rule-of-mixtures approximation, and strain and stress distributions were calculated for simulated cooling from an assumed fabrication temperature. The results demonstrate the importance of accounting for plasticity when comparing graded and nongraded interfaces. Significant geometrical effects on peak stresses were observed in the graded materials. It is shown that in some cases, optimization of the microstructure is required to achieve reductions in certain critical stress components believed to be important for controlling interface failure.