Fatigue evaluation of surface coated railway rails using shakedown theory, finite element calculations, and lab and field trials

One solution to prevent surface fatigue of rails, investigated by the European project INFRA-STAR, is to coat the surfaces with a material which reduces or eliminates ratchetting. In this investigation, a systematic approach for fatigue design of surface coated rails (called two-material rails) against rolling contact fatigue is presented. It incorporates dynamic train-track interaction simulations, three-dimensional finite element (FE) calculations, shakedown theory, and lab and field trials. The approach was validated against two-dimensional twin-disc tests in laboratory, where surface coated disc specimens were used. Next, heavy haul traffic field trials were performed using two-material rails. Dynamic train-track interaction simulations, for train traffic situations at the test site, were performed. The results from these simulations were contact load data, which were used in the fatigue design approach to calculate railhead stresses with a three-dimensional FE model of a piece of rail; 26 load cases were identified as critical with respect to rolling contact fatigue. The stresses from the FE calculations were used to calculate shakedown diagrams for various wheel-rail contact situations at the test site. The shakedown diagrams and calculations are used to illustrate how the improvement in shakedown performance of coated rails varies with the coating thickness, traction coefficient, contact load position, the strength of the coating and substrate materials, and strain hardening of the materials. It is shown that the two-material rails with the correct rail profile can be used to prevent rolling contact fatigue and reduce wear for the current train traffic situation. The results are discussed in the light of observations at the test site.