CREEP-FATIGUE LIFE PREDICTION OF IN-SITU COMPOSITE SOLDERS

Eutectic tin-lead solder alloys subjected to cyclic loading at room te mperature experience creep-fatigue interactions due to high homologous temperature. Intermetallic reinforcements of Ni3Sn4 and Cu6Sn5 are in corporated into eutectic tin lead alloy by rapid solidification proces ses to form in Situ composite solders. In this study, the in situ comp osite solders were subjected to combined creep and fatigue deformation at room temperature. Under cyclic deformation, the dominant damage me chanism of in situ composite solders is proposed to be growth of cavit ies. A constrained cavity growth model is applied to predict creep-fat igue life by taking into account the tensile loading component as well as the compressive loading component when reversed processes can occu r. An algorithm to calculate cavity growth in each fatigue cycle is us ed to predict the number of fatigue cycles to failure, based on a crit ical cavity size of failure. Calculated lives are compared to experime ntal data under several fatigue histories, which include fully reverse d stress-controlled fatigue, zero-tension stress-controlled fatigue, s tress-controlled fatigue with tension hold time, fully reversed strain -controlled fatigue, and zero-tension strain-controlled fatigue. The m odel predicts the creep-fatigue lives within a factor of 2 with the in corporation of an appropriate compressive healing factor in most cases . Discrepancy between calculated lives and experimental results is dis cussed.