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 1 mm 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.