A high fatigue life prediction methodology under constant amplitude multiaxial proportional loadings

Abstract

The main aim of this study is to propose a method for prediction of the fatigue-life for different materials subjected to constant amplitude multiaxial proportional loading. The paper presents a method to solve a high-cycle-fatigue problem using linear elastic analysis via Ansys software. A computing program of the fatigue life prediction methodology was developed. This program uses both Ansys and Matlab files. It is necessary to build an interface which allows both softwares to interact. The fatigue life N can be evaluated from knowledge of both the equivalent stress and the SN curves in reversed torsion and alternating bending. The numerical simulation provides to evaluate the fatigue life N and to localize the critical region. We test the model on a carbon steel type S 45C. To demonstrate the use of algorithm developed in this work, two case study problems were solved. The first case consists of a rectangular plate, with low thickness, which is subjected to uniaxial tensile stress combined with alternating bending moment. The second case concerns a specimen, with circular cross-section, which is subjected to uniaxial tensile stress combined with alternating torsion moment. The loadings which cause infinite-life and those which generate finite-life could be distinguished. The model can also determine the safe domains in the frame with axis load forces, in order to choose the adequate force loads. For a given fatigue life, the model predicts a continuous linear relationship in which the amplitude of the alternating force decreases as the uniaxial tensile stress increases.