Fatigue crack propagation in resonating structures

Abstract

Fatigue crack propagation in structures excited at one of their resonances is investigated. The structure is discretized and represented by a system of linear differential equations. Cracks are modelled as local flexibilities. Application on a 4-node rotor with a circumferential crack illustrates the dynamic crack arrest. The depth of the crack determines the local stiffness introduced by the crack, which in turn influences the dynamic response of the system under external excitation of constant amplitude at a resonant frequency. The propagation of the crack introduces additional flexibility which causes gradual shift from resonance. The dynamic response is reduced and, under certain circumstances, becomes less than a threshold value characteristic of the material considered. This phenomenon, known as dynamic crack arrest is drastically influenced by the loss coefficient of the material which is the main factor to determine the crack propagation rate at the initial stages of the crack growth when the loading of the cracked section becomes maximum.