On the Characterization of Thermal-Conductivity Degradation During Torsional Fatigue

Abstract

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.

Nondestructive Evaluation of Early Contact Fatigue Using Eddy Current Pulsed Thermography

“…, and can be written for the derivatives in the following equation (6). (6) As the fatigue damage occurs at the area that suffers contact fatigue, the thermal and electrical conductivities of samples are varied [37][38][39]. Thus, both the spatial and transient of heat distribution is non-uniform at these areas.…”

“…During the fatigue process, the microstructure of the gear is changed. These changes lead to a considerable decrease in thermal conductivity, electrical conductivity and magnetic permeability [37][38][39]. The relationship between the heat distribution and these parameters can be established by using the pulsed eddy current thermography method.…”