Low‐cycle Fatigue Under Non‐proportional Loading

A series of strain‐controlled, low‐cycle fatigue experiments have been conducted on 42CrMo steel under various loading paths including circular, square, cruciform, and rectangular paths. Present experiments have shown that there is additional hardening under non‐proportional cyclic loading. Non‐proportional cyclic additional hardening also results in a shorter life for multiaxial low cycle fatigue. A non‐proportionality measure of strain path based on both a physical basis and macromechanical phenomena is proposed. The loading path effect on additional hardening is also described well. Low‐cycle fatigue damage accumulation and the evolution process under non‐proportional loading is analysed via the Continuum Damage Mechanics Model of Chaboche. A non‐proportinality measure is introduced in the damage evolution equation and a modified Coffin‐Manson type formula is derived. A novel fatigue life prediction approach based on the critical‐plane concept of Brown and Miller is proposed.