Thermomechanical fatigue of a lead alloy

Abstract

The effects of superimposing a thermal cycle onto a strain-controlled fatigue cycle have been studied for a lead-base alloy containing a minor amount of tin. These tests have been conducted at temperatures near half the melting point under conditions of cycling which included strain ranges from 0.3 to 3 pct and periods between 184 and 1040 seconds per cycle. Cracks were seen to initiate rapidly as grooves along grain boundaries and grow inward until a drop in the load-carrying capacity of the sample was observed when a significant fraction of the crack population exceeded approximately 300 μm in depth. The presence of an in-phase thermal cycle was seen to substantially reduce the number of cycles to failure relative to a reference isothermal test at the highest temperature of the thermomechanical cycle. For a given set of test conditions, the number of cycles to failure increased with the angle of phase lag of the mechanical cycle with respect to the thermal cycle. Decreasing frequency was found to increase the number of cycles to failure in thermomechanical fatigue (TMF), while the opposite was observed for the isothermal reference tests. Hold time was found to reduce the number of cycles to failure in TMF.