Analysis of revised fatigue life calculation algorithm under proportional and non-proportional loading with constant amplitude

• A revised fatigue life calculation algorithm is presented.
• In the revised algorithm the material parameters are functions of fatigue life.
• The algorithm is convergent under cyclic proportional and non-proportional loading.
• Calculated and experimental fatigue lives are more consistent.

This paper reports the results of a study into a revised algorithm applied to the fatigue life calculation under cyclic multiaxial proportional and non-proportional loading. In contrast to the classical algorithm, which assumes that material parameters in the fatigue criterion are constant, the revised algorithm relates the values of these parameters to the number of cycles to failure. The objectives in this paper include verification of the convergence for the revised algorithm and evaluation of the fatigue life calculation by use of the revised algorithm. Detailed implementations of the multiaxial fatigue criteria by Matake and Papadopoulos are presented for the algorithm. The calculated fatigue lives are compared to the experimental ones for three steel grades: SAE1045, S355J2G and SM45C subjected to cyclic uniaxial and multiaxial proportional and non-proportional loading. It is shown that the revised algorithm provides a sole solution under the proportional and non-proportional loading by application of the Matake and Papadopoulos criteria. A higher convergence between experimental and calculated fatigue life is obtained for the revised algorithm than for the classical one.