Investigation of Effect of Creep Strain on Low-Cycle Fatigue of Lead-Free Solder by Cyclic Loading Using Stepped Ramp Waves

Abstract

The fatigue life of a material varies with the strain rate if it has time-dependent deformation. An interesting phenomenon related to the effect of the strain rate on the fatigue life can be observed when a cyclic tension-compression loading of which strain rate in the tensile region is different from that in the compressive region is employed for the fatigue test. Different fatigue lives due to different strain rates in the tensile and compression regions originate from the difference of development behaviors of creep strain generated in the cyclic loading. This paper investigates the effects of creep strain on the difference of fatigue life due to the different strain rate in the tensile and compression regions. The creep strain of the lead-free solder Sn–3.0Ag–0.5Cu subjected to a cyclic loading was investigated using stepped ramp wave loading. The experimental results reveal that the creep strain develops differently in the tensile and compression regions. A new parameter is proposed for estimating fatigue life when the strain rate varies in the loading direction.