Johan Sandström

Numerical Study of the Mechanical Deterioration of Insulated Rail Joints

Abstract Numerical simulations are performed to study plastic deformation and fatigue impact of an insulated joint. The simulations feature a sophisticated constitutive model capable of capturing ratcheting under multi-axial loading conditions. Calculation results are presented in the form of effective strain magnitudes, plastic zone sizes, and multi-axial low cycle fatigue parameters. The simulation results indicate that the main damage mechanism at insulated joints is ratcheting and not low cycle fatigue. A parametric study quantifies effects of increased vertical and longitudinal load magnitudes, as well as the effect of an increased insulating gap. In particular, longitudinal loading is indicated as being severely deteriorating for the rail in the vicinity of the joint. Finally, the effect of rail edge bevelling is assessed and found to be small for the case studied.

Predicting crack growth and risks of rail breaks due to wheel flat impacts in heavy haul operations

Abstract The risk for rail breaks is investigated from mechanical and statistical points of view with particular focus on the influence of impact loads from flatted wheels. For a presumed rail head crack geometry and rail temperature, the stochastic relation between the crack position along the rail and the wheel flat impact position results in a risk of fracture. In addition to the analysis of the risk for final fracture, rail crack growth is also studied. In particular, the contribution of wheel flat impacts on crack growth rates is quantified. The study takes the form of a dynamic load analysis that evaluates rail bending moments due to wheel flat impact. Then, a fracture mechanics analysis is employed to establish stress intensity factors for rail head cracks under bending and temperature loading. These analyses are then combined to give risks of rail breaks and to quantify crack growth rates for varying operational conditions.