The Effect of Temperature on Low Cycle Fatigue of an Eutectic Solder

Low cycle fatigue tests of eutectic solder alloy 63Sn37Pb were carried out over a wide range of temperatures (from 22degC to 125degC), and at each fixed temperature, different total strain ranges (from 1% to 10%) were loaded. The triangular waveform was employed for all the tests, and hysteresis loops data were automatically collected by data acquisition system. Relations between the maximum tensile load and number of cycle, and the load drop parameters under each test condition were calculated to describe the softening behavior of solder. Logarithmic values of cyclic stress and plastic strain range at half of the fatigue life were linearly fitted for each temperature. With different definitions of fatigue life, relationships between plastic strain range and low cycle fatigue life at different temperature were presented in Coffin-Manson model. At low temperature, the curve of load drop parameter has a flat slope which indicates a slow softening of the solder alloy, and the slope becomes steeper as temperature increases. The curve of maximum tensile load versus number of cycle has approximately the same trend as the load drop parameter curve. As temperature increases, the slope of the cyclic stress and strain plot increases, namely the cyclic strain hardening exponent becomes larger. It is also found that the fatigue exponent m in Coffin-Manson model only decreases slightly with increasing temperature, but the ductility coefficient C decreases evidently as temperature increases. Finally, the Coffin-Manson model is modified so that the temperature effect is included.