FEM Analysis of Thermal Cycle Effect on Residual Stresses of Ceramics/Metal Joints.

Abstract

Effect of a single thermal cycle on residual stresses of Si3N4/SUS 304 joints with an insert layer of copper was analyzed using the thermo-elastic-plastic finite-element method (FEM). The residual stress was found to increase after a single thermal cycle, which was consistent with the result of residual stress measurement by the X-ray diffraction method. The exponent and intensity coefficient of stress singularity at the interface edge on the ceramic side were also found to increase with the increase of thermal cycle temperature. The increase of residual stresses was thought to be caused by the elastic-plastic behaviour and strain hardening of the copper insert layer. The temperature dependence of the yield stress of copper was also considered. It was shown that the residual stresses at room temperature were controlled only by the yield stress of copper at room temperature. By applying the isotropic hardening rule and kinematic hardening rule in the analysis, it was found that the constitutive (stress-strain) relation of copper was a problem which must be solved in predicting residual stresses under multiple thermal cycles.