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Engineering Fracture Mechanics, Volume 85, May 2012, Pages 47-58
Mohammadali Farjoo, William Daniel, Paul A. Meehan
School of Mechanical and Mining Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
Abstract
Rolling contact fatigue cracks in railway track called squats are studied in this paper. In the first part, the effects of an elasticfoundation (sleepers and the ballast) on stress intensity factors obtained at acrack tip are studied. A simplified finite element model (FEM) and an extended finite element model (XFEM) were created to investigate these effects, the XFEM model being limited in geometrical size, but more able to model crack growth. Both FEM and XFEM confirmed that an elasticfoundation leads to an additional bending stress which increases the crack growth rate significantly. Field results also authenticate that squatformcracks appear on timber sleepers more commonly than on concrete ones. These results indicate that considering these bending stresses in a FE model, is important to achieve a more realistic model of squat development. In the second part, a short crack of 250 um length is simulated to investigate how variations of traction ratio (TR), friction coefficient between the crack faces (FC) and the crack angle affect SIFs when the rail is mounted on an elasticfoundation. Simulations show that acrack on araillaid on elasticfoundation (clips, sleepers and ballast) can lead to significantly higher SIFs in many conditions and consequently raises crack growth rate. This indicates that foundation stiffness is as important as water entrapment and friction coefficient between the crack faces.
