The Endochronic Viscoplasticity for Sn/3.9Ag/0.6Cu Solder Under Low Strain Rate Fatigue Loading Coupled with Thermal Cycling

Abstract

AbstractIn this paper a wide range of temp. dependent kernel function ρ(Z) and the strain-rate function h(, T) in the Endochronic viscoplasticity were established first by using experimental steady hysteresis loops of Wei et. al., for Sn/3.9Ag/0.6Cu Solder at fixed 298K or 373K and strain rate at 10−3, 10−4 and 10−51/s; and then extended to predict the thermomechanical behavior of solder under constant low strain rate (10−51/s), from 0 to 1% max. strain fatigue loading with in-phase thermal cycling between 298K and 373K.A novel approach in the theory to account for the microstructural changes enhanced by the stressassisted grain boundary diffusion mechanism during thermal cycling was proposed by using a partial relaxation function h1(T) of back stress (i.e. ρ0 in ρ(Z)).The theoretical results were in very well agreement with experimental data. These results and the out-phase results from the present theory were new and might be used as references to compare with results derived from other theories.