The crack path prediction and fatigue durability estimation based on the damage function approach

Abstract

In the process of the material degradation under cyclic loading is usually distinguishing several stages such as crack initiation, crack growth and final fracture. The local stress stage is changing with the degradation process and especially during the crack growth stage. The convenient approach to predict the total fatigue life is usually based on two different problems: (1) use of a multiaxial criterion to estimate duration of the crack initiation; (2) used of Paris law to estimate the stable crack growth duration. However, during the evaluation of stress state a different crack opening modes can act. This change is clearly observed in the case of pure torsion loading. The propagated torsion crack combines normal and shear crack opening stages. The convenient approaches are not suitable to predict such fatigue behavior of structural elements. This paper is introducing a new approach to estimate the total fatigue life, including the crack initiation and propagation stages, with regards to crack opening mechanisms. The proposed approach is based on the modern model of the full SN curve, damage theory and takes into an account the normal and shear mechanisms of fatigue damage accumulation. The paper contains the result of numerical simulation for VHCF torsion tests prediction.