Effect of inelastic multiaxial preloading on high cycle fatigue strength

This study investigates an effect of inelastic non-proportional preloading on failure life in a followed high cycle fatigue for two steels, SUS316 stainless and Mod.9Cr-1Mo steels. Preloading tests were conducted using a servo controlling hydronic multiaxial fatigue testing machine which can apply an axial loading and torsional loading. Two types of loading paths under strain controlled were employed: a push-pull loading and a circle loading. The circle loading is the non-proportional loading in which axial strain ε and shear strain γ have 90-degree difference. Using the specimens fatigued in the inelastic preloading test, high cycle fatigue tests were conducted by a rotating bending fatigue testing machine. Based on the obtained results, effects of inelastic proportional and non-proportional preloading on the failure life in high cycle fatigue is discussed. The high cycle fatigue life for SUS316 stainless steel such as the materials of which crystal structures are FCC was increased due to cyclic hardening depending on inelastic non-proportional preloading. On the other hand, the life for Mod.9Cr-1Mo steel which has BCC was reduced by the cyclic softening induced by the preloading. (author)