Finite element modelling of crack propagation under vibration spectrum based on local tip continuum damage dynamics

The shift of the dynamic response of a structural part during the propagation of embedded defects may have a significant effect over its remaining fatigue life, of particular relevance in components subjected to severe vibration environment. Traditional high cycle fatigue approaches predict the safe-life of the part based on the number of cycles required for fatigue crack nucleation, i.e. based on an un-propagated crack condition stress state. This work prospects the incorporation of a local tip-based continuum damage model into the elastodynamic finite element discretization of cracked specimens exposed to vibratory excitation. The resulting ‘continuum damage dynamics’ algorithm performs the coupled, interdependent updates of fatigue damage accumulation, modal decomposition and dynamic response at each step of the simulation. The study explores scenarios of excitation close to resonance and assesses the sensitivity to the damping ratio, the mesh size and the material characterization for the plasticity-dominated region surrounding the crack tip. The proposed numerical scheme allows to estimate the fatigue life and to recreate the dynamic crack propagation measured in physical tests with fixed and random forcing frequencies.