Numerical Calculation of Crack Parameters for Propagation Assessment in a Complex Component with Residual Stresses

Abstract

Fatigue is an actual issue, especially in the structural assessment of highly critical components where failure may provoke the loss of the whole system they belong to. This is especially true in a damage tolerant scenario. In this case the use of a component is permitted even after damage has occurred, but extensive knowledge of the damage status and the effect of the damage on the reliability of the component is required. An experimental approach to damage tolerance is often very complex both for the damage creation and for the subsequent step of fatigue tests. A reliable and efficient methodology for fatigue simulation and crack propagation is therefore of interest both from a theoretical and an industrial point of view. The aim of the paper is to investigate crack parameters in a transmission shaft subjected to ballistic impact damage; cracks can nucleate from the point of damage and propagate due the application of service loads Starting from the outcome of a FEM simulation of a ballistic impact, different strategies for numerical crack propagation under service loads are presented and assessed. Specifically the damage under investigation is composed of two holes separated by a septum. Experiments reveal that the crack that nucleates from one of the two holes is strongly influenced by residual stresses. The complexity and the variety of the phenomena involved (complex damage, presence of residual stresses, shape of the component) make the numerical simulation of the phenomenon not trivial and give grounds for a thorough investigation of different modelling approaches.