This study investigates the fatigue life of automotive connector solder joints under combined thermal and vibration loading, considering microstructural coarsening that occurs during service. A unified fatigue life calculation framework was established based on FEM simulations incorporating microstructure-dependent constitutive models and fatigue laws. By updating the microstructure over time via user subroutines, both thermal and vibration damage were evaluated and combined to predict total life. The results revealed that microstructural coarsening significantly reduces fatigue life and that the influence of vibration damage, initially negligible, becomes dominant as coarsening progresses. These findings highlight the importance of accounting for microstructural evolution in fatigue reliability assessment under combined loading.
YAMAZAKI et al. (Wed,) studied this question.