Thermal residual stresses in a functionally graded material system

A one-dimensional calculation of thermal residual stresses, arising from the fabrication of a Functionally Graded Material (FGM) system, is presented. As a first step, calculations have been limited to the linear elastic case. The FGM system consists of ceramic (Al2O3) and metal (Ni) phases varying with distance in one direction. Several functional forms of gradation of constituents were examined to arrive at the optimum profile giving the minimum residual stress level. A linear variation in composition from fully ceramic to fully metal showed the least residual stress. Residual stresses were found to increase when fully ceramic and/or fully metal regions are included in the structure, adjoining the graded zone. The character (tension or compression) of stresses is dependent on the functional form of gradation. A low residual stresses state close to that of the continuously graded structure can be achieved also in a multilayer FGM system having several layers (typically > 11) of constant composition. The effects of temperature dependent elastic and thermal expansion characteristics of constituents on residual stress were found to be small.