Theoretical and experimental analysis of relation between entropy and tension–compression fatigue of aluminum 6061-T6

Abstract

Fatigue life is one of the key parameters in investigating the elements which are under cyclic loading. It is known that during the fatigue loading, temperature of the specimen increases due to hysteresis heating which is referred to as the fatigue entropy. It has been also proven that when a metal experiences cyclic loading, the entropy at the failure point has a constant value. This research contains both analytical and experimental parts. A series of axial fatigue test are conducted on aluminum alloy 6061-T6 specimen, and temperature evolution is obtained under the fully reversed tension–compression cyclic loading. The variation of temperature in the material during loading is then used to compute the fatigue fracture entropy of the material. Then, the number of cycles to failure is calculated by using the relation between entropy and fatigue life. An empirical relation from tension–compression fatigue loading is derived which can link the temperature rise rate at the initial stage of the test with the number of cycles to failure. In the analytical part, the commercial finite-element software is used to find the temperature evolution under the fully reversed tension–compression cyclic loading by elastic plastic finite-element analysis. A combined hardening model of Chaboche is applied for estimating the material parameters. The comparison between the theoretical and experimental results is shown and discussed.