Estimating the notch and mean stress effect in fatigue through the degree of multiaxiality of the local elasto-plastic stress/strain fields

The present paper is concerned with the estimation of fatigue lifetime of engineering materials by directly taking into account the degree of multiaxiality of the local elasto-plastic stress/strain fields acting on the fatigue process zone. The proposed approach takes as a starting point the assumption that Stage I is the most important stage to be modelled to accurately predict fatigue damage. This is done through the so-called Modified Manson-Coffin Curve Method (MMCCM), which postulates that the critical plane is that material plane experiencing the maximum shear strain amplitude. Subsequently, the MMCCM is used to show that the mean stress effect in fatigue can directly be addressed as a problem of inherent multiaxiality. Finally, the above critical plane approach is reformulated in terms of the Theory of Critical Distances (TCD) in order to correctly account for the detrimental effect of stress/strain gradients arising from stress concentration phenomena.