Strain-rate effects on low cycle fatigue mechanism of eutectic Sn–Pb solder

Low cycle fatigue tests of as-casted Sn–Pb eutectic solder (63Sn/37Pb) were carried out using the non-contact strain-controlled system at 20°C in order to avoid local deformation and stress concentration at contact points between the extensometer and the specimen surface. The fatigue mechanisms were studied by SEM examination of polished surface of specimens and fracture surfaces. Wedge cracking due to grain boundary sliding was the dominant mechanism in the low strain rate regime, while extensive cavitation was observed on the colony boundaries at high strain rate regime. An estimation of the transition strain rate for grain boundary cracking due to sliding (ε̇∗w) yielded a value lowers than that of the experimental result by 2–3 orders of magnitude. Relationship between time to failure and strain rate for the present results and the reported results could be expressed by a double-linear curve with the transition strain rate of approximately 10−3 s−1.