On the Characterization of Thermal-Conductivity Degradation During Torsional Fatigue

The thermal conductivity of a metal, subjected to cyclic loading, changes as it degrades due to the appearance of micro-cracks and micro-voids. This continues up to the critical stage where macro-cracks are created and failure occurs. In this study, a theoretical model for thermal-conductivity deterioration is presented that accounts for the cyclic loading. To examine the validity of the results obtained from a theoretical model, an apparatus is designed to measure thermal-conductivity degradation by means of the guarded-comparative-longitudinal heat-flow technique. Results of a series of thermal-conductivity measurements at several stages of torsional fatigue tests are presented. It is shown that the thermal conductivity of Al 6061-T6 decreases approximately 8 % to 12 % before complete failure takes place.