非比例負荷におけるSn-8Zn-3Biはんだの多軸低サイクル疲労寿命

抄録

This study describes evaluation of multiaxial low cycle fatigue life of a lead-free solder, Sn-8Zn-3Bi. Strain controlled multiaxial low cycle fatigue tests under proportional and non-proportional loading conditions were carried out using a hollow cylinder specimen at room temperature. The loading conditions employed were a push-pull, a reversed torsion, a box-shape, a step-shape and a circle-shape strain paths. The former two loading conditions are the proportional loading and the latter three loading conditions are the non-proportional loading in which directions of principal stresses and strains are changed in a cycle. The effect of non-proportional loading on the fatigue life of Sn-8Zn-3Bi was investigated. The reduction in low cycle fatigue life due to non-proportional loading was identified, and the life was the shortest for the circle-shape strain path when fatigue lives were correlated by a von Mises equivalent strain range. Fatigue lives of four strain paths other than the reversed torsion strain paths were correlated within a factor of two band by an equivalent inelastic strain range. All of the fatigue lives were evaluated well by a non-proportional strain range considering the effect of additional strain hardening due to non-proportional loading, which was proved to be effective for life evaluation of the solder under non-proportional loading.