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Low cycle fatigue (LCF) behavior of commercially pure titanium (CP-Ti) was investigated under stress cycling and strain cycling along the rolling direction (RD), 30° to the rolling direction (RD-30°), 60° to the rolling direction (RD-60°) and the transverse direction (TD), respectively. The loading direction brings about eminent differences in the fatigue properties, which is summarized as follows; Cyclic strain hardening exponent: RD＞RD-30°＞RD-60°＞TD Cyclic stress amplitude: TD＞RD-60°＞RD-30°＞RD Ratcheting effect: TD＞RD-60°＞RD-30°＞RD Fatigue life: RD＞RD-30°＞RD-60°＞TD Based on the comprehensive analysis of Schmid factor, texture evolution, twinning activities, in-grain misorientation axis and geometrically necessary dislocation density, it is concluded that the anisotropic slip behavior characterizes the planar anisotropy of LCF behavior. The promotion of dislocation activities of non-prismatic slip with higher activation stress from the RD to the TD leads to the higher cyclic stress amplitude, lower cyclic strain hardening and more significant ratcheting effect, though prismatic slip always acts as the primary slip mode. The observation of fracture surfaces also confirms the critical role of dislocation activities on fatigue crack initiation. Introducing yield ratio parameter into the asymmetry coefficient related model, the fatigue lives in both the fatigue were accurately predicted. [ABSTRACT FROM AUTHOR]

The role of thermal cycling on the deformation behaviour and microscopic damage mechanisms of 316L stainless steel are clarified through isothermal fatigue (IF) and thermomechanical fatigue (TMF) tests under various temperature ranges. Corresponding microscopic damage mechanism is revealed based on the analysis of dislocation structure, plastic deformation, and crack initiation mode. Results show that the introduction of thermal cycling, as well as an increase in average temperature and temperature difference, result in the saturation of cyclic peak stresses, a decrease in fatigue life, and an intensification of dynamic strain ageing (DSA). Notably, under TMF loading at the same average temperature, there is a significant recovery process compared to IF. High-density dislocations transform into low-energy dislocation structures through cross-slip, indicating a pronounced recovery phenomenon. At large temperature differences and high average temperatures, the accumulation of dislocation tangles at grain boundaries and the formation of dislocation cell structures lead to severe incoherence in plastic deformation and the accumulation of damage. Furthermore, the introduction of thermal cycling and an increase in temperature differences also induce severe creep damage. It is observed that the dominant crack initiation mode changes from fatigue-dominated transgranular cracking to oxidation-induced intergranular cracking as the average temperature increases. Finally, a modified life prediction model is developed by incorporating thermal plastic strain energy to reflect the effect of thermal cycling on TMF behaviour. [ABSTRACT FROM AUTHOR]