Analysis of surface crack growth under rolling contact fatigue

Understanding the fatigue crack growth phenomenon in railheads requires a study of driving forces, such as the crack tip opening and sliding displacements, under repeated rolling contact. Finite element simulations, allowing elastic–plastic deformation, and mixed-mode crack growth laws were utilized to demonstrate that the fatigue crack growth rates display a minimum after a finite amount of crack advance. These results have implications in designing strategies for optimum grinding or wear rates to limit fatigue crack growth, and thereby prolong rail life. During the simulations, the crack was allowed to advance, permitting residual deformations and stresses to be retained from cycle to cycle. The opening and closure of crack surfaces, under forward and reverse slip and stick conditions were monitored. Normal pressures of 1500 MPa and 2000 MPa, along with shear traction ratios in the range of −0.4 to 0.4 were investigated for a varying crack size of 3–15 mm. An interesting finding was that the crack tip opening displacements decreased while the crack tip sliding displacements increased with increasing crack length.