Elastic-Plastic-Creep Simulation of Pb/Sn Solder Alloys by Separation of Plastic and Creep

This paper describes a constitutive model for solder alloys and a method to determine the material parameters of the model. First, a constitutive model that divides the inelastic deformation into plastic and creep parts is proposed. Next, a numerical method for the determination of the material parameters used in the model is developed. In this method, the material parameters for the creep part are determined first by pure tensile tests at different strain rates, and the creep strain is calculated next. Subtracting the calculated creep strain from the pure tensile deformation, the stress-strain relation for the time independent strain is obtained. Then, the material parameters for the time independent strain, such as the elastic and plastic strain, are simply determined from the obtained stress-strain relations. Simulations of the stress relaxation after several different preloadings were carried out to verify the accuracy of the proposed model and numerical method.