Additional cyclic strain hardening and its relation to material structure, mechanical characteristics, and lifetime

The authors have analyzed the susceptibility of metallic materials to cyclic strain hardening depending on both their microphysical characteristics and macrophysical parameters represented by standard mechanical characteristics. At the microlevel, the degree of additional hardening is related to the material stacking fault energy. The materials with a high level of the stacking fault energy do not exhibit additional cyclic hardening under non-proportional loading, while those with a low energy are susceptible to a considerable strain hardening. For the macrolevel, on the basis of analysis of the mechanical properties of metallic materials, the authors have derived a correlation dependence between the hardening levels under static and cyclic loading. An approximate quantitative method to determine maximum strain hardening levels under non-proportional low-cycle strain-controlled loading is proposed. The lifetime under non-proportional loading has been shown to correlate well with the level of additional hardening.