Rail rolling contact fatigue response diagram construction and shakedown map optimization

The shakedown map is one of the key prediction models used in railway engineering to evaluate rolling contact fatigue (RCF) damages of wheels and rails. The objective of this work is to construct the response diagram of RCF and optimize the classical shakedown map based on the rolling-sliding tests. A method based on rolling-sliding tests for constructing the response diagram was presented. Firstly, the traction coefficient (μ) and load factor (P0/ke) were taken as the X-axis coordinate and Y-axis coordinate of the coordinate system of the classical shakedown map, respectively. Then, test parameters (P0 and μ) were designed and obtained using the various X and Y coordinate in four different regions of shakedown map (i.e., different plots of μ versus P0/ke). After that, for various test parameters, the rolling-sliding tests were carried out using a twin-disc testing apparatus under dry condition to investigate the RCF damages of U75V rail steel. The results showed that three types of damage states could be observed after rolling-sliding tests under different test parameters: (I) neither plastic flow of materials nor fatigue cracks, (II) plastic flow, and (III) fatigue cracks with plastic flow. Thus, the response diagram consists of the above three damage regions. Furthermore, with the increase of P0 and μ, all the depth of plastic flow, the length of fatigue cracks and the wear rates were increased. Moreover, materials were work hardened in the damage states of plastic flow and fatigue cracks. The hardness increment was increased with P0 and μ. In addition, the boundary of ratchetting region (i.e., shakedown limit) in the classical shakedown map for partial slip was optimized based on the RCF damages and the new response diagram. The shape of optimized shakedown limit curve was same as that of the classical one, whereas the position of the optimized curve was decreased.