Evaluation of multiaxial low cycle fatigue cracks in Sn-8Zn-3Bi solder under non-proportional loading

Multiaxial low cycle fatigue damage of a lead-free solder Sn-8Zn-3Bi under non-proportional loading was evaluated. In non-proportional loading tests, a larger number of cracks were observed on the specimen surface compared to the proportional loading tests, and their directions were diverse due to direction change in stress and strain. In the circle loading test in which axial and shear strain have a 90° phase difference, the number of cracks rose from very early stage of the fatigue life, and their increasing rates were higher than those in a push-pull loading test. Apparently, non-proportionality of loading accelerates the formation of cracks and changes failure process during the tests.