Application of local and non-local approaches to multiple fatigue crack initiation and propagation

Abstract

Fatigue strength conditions presented in terms of normalized equivalent stress functionals defined on loading processes are used to unite the stages of material damage with fatigue crack initiation and multiple crack propagation under arbitrary loading history. Examples of employing the local form of the functionals associated with the Palmgren-Miner linear damage accumulation rule and the power-type S–N diagram to a periodic crack system are given and shortcomings of the local approach are pointed out. A non-local approach free from the shortcomings is described. Equations for curvilinear crack growth rate vectors taking into account the whole damage history ahead of the crack are presented for multiple cracks under mixed-mode loading