Crack propagation in rails based on the concept of material forces

Övrigt konferensbidrag, 2011

To properly simulate the propagation of an existing crack, we need to model how fast and in what direction it grows. A Generalized Crack Driving Force (GCDF), based on the concept of material forces cf. [1], is used to formulate a framework for crack propagation models. This framework can be used to formulate different crack propagation strategies: Explicit Proportional Extension (EPE), Implicit Proportional Extension (IPE) and Maximum Parallel Release Rate (MPRR), cf. [2]. Here, it is shown that all three strategies produce quantitatively good results compared with experiments, for the case of a three point bending test with an eccentric edge crack and internal holes [3]. In railway applications, highly complex loading cases arise in the wheel–rail interface, due to a moving contact load. For this particular loading case it is observed that the perpendicular component of the GCDF is highly dependent on the chosen parameters of the numerical algorithm. Hence, it is concluded that only the MPRR method remains applicable as it is only dependent on the parallel component of the GCDF and therefore more robust. Furthermore, the high loads in the wheel-rail interface result in large plastic deformation whereby the fracture resistance of the material becomes anisotropic [4]. Based on the MPRR method, the propagation of a single head check crack in a piece of rail, under realistic Rolling Contact Fatigue (RCF) loading conditions, is simulated by the use of a 2D FE model incorporating elastoplastic material behaviour. Finally, results from the simulations are presented and qualitatively compared to field observations.