Low cycle fatigue life prediction of 63Sn–37Pb solder under proportional and non-proportional loading

Multiaxial fatigue tests were conducted on 63Sn–37Pb solder specimens under proportional and non-proportional axial/torsional loading. The von Mises equivalent stress and strain are found to be fitted by the Ramberg–Osgood relationship. No additional hardening is observed under non-proportional loading, and the material fails in shear mode. Seven fatigue parameters are evaluated with life data obtained in the tests. It is found that the equivalent strain method overestimates lives under non-proportional loading, and that the maximum shear strain, the Kandil–Brown–Miller and the Fatemi–Socie parameters predict lives within a factor of two, but with a little non-conservatism for non-proportional loading cases. The Socie, Chen–Xu–Huang and Lee–Kim–Nam parameters yield life estimates within a factor of two with slight overall conservatism. The effect on fatigue life of normal strain or stress on the maximum shear strain plane is found rather small for critical plane theories.