A CRITICAL PLANE APPROACH TO MULTIAXIAL FATIGUE DAMAGE INCLUDING OUT‐OF‐PHASE LOADING

Abstract— A modification to Brown and Miller's critical plane approach is proposed to predict multiaxial fatigue life under both in‐phase and out‐of‐phase loading conditions. The components of this modified parameter consist of the maximum shear strain amplitude and the maximum normal stress on the maximum shear strain amplitude plane. Additional cyclic hardening developed during out‐of‐phase loading is included in the normal stress term. Also, the mathematical formulation of this new parameter is such that variable amplitude loading can be accommodated. Experimental results from tubular specimens made of 1045 HR steel under in‐phase and 90° out‐of‐phase axial‐torsional straining using both sinusoidal and trapezoidal wave forms were correlated within a factor of about two employing this approach. Available Inconel 718 axial‐torsional data including mean strain histories were also satisfactorily correlated using the aforementioned parameter.