Abstract
The fatigue life of solder alloys for the slow-fast cyclic loading condition is much shorter than that for the fast-slow cyclic loading condition, despite the two loading conditions having almost equal inelastic strain amplitudes. This suggests that the inelastic strain amplitude is not the best parameter used for evaluating the fatigue life which shows the strain rate dependency. In the previous study, we conducted the fatigue tests using the Sn-3.0Ag-0.5Cu (SAC) solder at RT. The tests employed the cyclic tension-compression loading using the stepped ramp wave (SW) to analyze the stress-creep strain relations during the tests. The analysis result showed that the creep strain amplitude obtained from the stress-creep strain relation had a higher correlation with the fatigue life than the inelastic strain amplitude. In addition, the equation indicating the relationship between the creep strain amplitude and the fatigue life at RT was likely to be useful to predict the fatigue lives at the other temperature. In this study, we investigated the relationships between the creep strain amplitude and the fatigue life for the SAC solder at 343 K and 393 K by conducting the fatigue tests with cyclic tension-compression loading using the SW. Then we attempted to describe the investigated relations at these two temperatures by the above-mentioned equation. As a result, the equation almost expressed the relationships between the creep strain and the fatigue life at 343 K and 393K even though it had been derived from the test results at RT.
