Multiaxial Creep-Fatigue of 63Sn-37Pb Solder at Elevated Temperature

Abstract

This paper describes the multiaxial creep-fatigue of 63Sn-37Pb solder solid and tube specimens in push-pull and reversed torsion using fast-fast, slow-fast, fast-slow and slow-slow strain waves. The strain rate of fast straining was 0.5%/s and that of slow straining was 0.005%/s. The suitability of multiaxial strain parameters for correlating multiaxial creep-fatigue lives was discussed. Mises' strain and maximum shear strain were an appropriate parameter for the data correlation. The largest fatigue lives were found in fast-fast strain wave test and the smallest ones in slow-fast test. The fatigue lives in slow-slow test were somewhat smaller than those in fast-fast test, but there was no large difference in fatigue life between the two strain waves. Main cracks of which length was more than 1mm were initiated and propagated in fast-fast and slow-slow tests but many small cracks whose length was less than 100 micron meter were initiated and no long main cracks were propagated in slow-fast and fast-slow tests. These crack behaviors corresponded with the stress change with cycles. Stress amplitude rapidly decreased with cycles in the final stage of life in fast-fast and slow-slow tests due to the main crack extension but it gradually decreased with cycles in slow-fast test resulted by the extension of many small cracks. Deformation of grains in slow-fast and fast-slow tests was discussed in relation with the micro rachet deformation of grain boundaries.