Evaluation of high-temperature fatigue life of aluminium alloys using plastic-creep separation method

Abstract

In order to evaluate low cycle fatigue life under thermo-mechanical loading including high temperature regions, it is necessary to understand the basic deformation characteristics of a target material. In the case of thermo-mechanical loading, especially, the strain rate dependence for each temperature region must be clarified because there are some temperature regions that are greatly affected by the creep deformation. However, a few studies have investigated the effect of creep deformation on low-cycle fatigue life evaluation considering thermo-mechanical fatigue evaluation. In this study, a low cycle fatigue test at 623 K, which is a higher temperature region than Tm/2 for aluminium alloys is conducted, and a new fatigue life evaluation method using creep strain as an index is also discussed. Namely, a low-cycle fatigue test is performed with a cyclic tension-compression loading with a constant strain amplitude under different strain rates in the tension side and compression side. Furthermore, using the method for separating plastic strain and creep strain, which is proposed by the authors (Ohguchi and Sasaki), the inelastic strain is separated into plastic and creep strain. The correlations between the creep, and plastic strain and the low cycle fatigue life are clarified. Also, the low cycle fatigue life evaluation method using creep strain as an index is verified.

Keywords

• aluminium alloy
• low-cycle fatigue
• time dependency
• creep and plastic strain
• fatigue life evaluation