A unified viscoplastic model for characterizing the softening behavior of the Sn3.0Ag0.5Cu solder under monotonic and cyclic loading conditions

A viscoplastic model based on the Chaboche framework was developed to consider the behaviors of Sn3.0Ag0.5Cu solder under tensile, creep, relaxation and cyclic conditions at a wide range of temperatures. The experimentally-observed strong softening responses, especially at lower strain rates and higher temperatures, were modeled by incorporating evolutionary dynamic recovery parameters, which depend both on the accumulated viscoplastic strain and the strain memory surface. Temperature rate terms were also included to consider the thermomechanical response. The viscoplastic model parameters were obtained by using a two-step procedure and validated to experimental data by using Runge-Kutta and finite element simulations.