A new life prediction model for multiaxial fatigue under proportional and non-proportional loading paths based on the pi-plane projection

A new multiaxial fatigue damage parameter is proposed based on the projection path on the π-plane of the loading path. The proposed parameter is suitable for any arbitrary loading path in practical problems. Many materials exhibit strain hardening due to the non-proportional cyclic loading. A brief overview of some important non-proportional effects in multiaxial fatigue is presented, and a new non-proportionality description is defined. A modified multiaxial fatigue life prediction model is established based on the Coffin-Masson equation. Comparing to five classic multiaxial fatigue models, including the maximum effective strain model, the maximum shear strain model, the Fatemi-Socie (FS) model, the Smith-Watson-Topper (SWT) model and Itoh model, the predicted multiaxial fatigue lives of three metallic materials using the proposed model agreed better with the experimental results.