Shear–normal stresses interaction in multiaxial fatigue under nonproportional loading part 1: theoretical aspects and experimental investigation

Purpose This study aims to develop a new multiaxial stress state analysis. Design/methodology/approach The current two-part study proposes a new model to assess the interaction between shear-normal stresses in multiaxial fatigue life. The objective of these studies is to find a relationship between the fatigue behavior of shear and normal stresses, defined as the shear-normal stresses interaction and utilize it in fatigue life prediction of proportional and non-proportional loadings. In Part 1, a new multiaxial stress analysis is developed. Several proportional and non-proportional loadings are investigated in a parametric study. Through this investigation, five load parameters are identified. The proposed stress analysis is also extended to the high-strain loadings, including plasticity. The effects of the proposed load parameters on multiaxial fatigue are experimentally investigated and discussed. In Part 2, a new multiaxial fatigue model is proposed based on the load parameters introduced in Part 1. The validity of the proposed model is studied and compared with three well-known models. Findings The discussion of the experimental program reveals that the introduced load parameters are essential in multiaxial fatigue assessment. Research limitations/implications None known for this paper. Practical implications The introduced stress analysis method is novel in the field of multiaxial fatigue. This analysis method shows its ability to identify the essential multiaxial load parameters required for life assessment. Originality/value This paper fulfils an identified need to predict fatigue life under the proportional and non-proportional multiaxial loadings.