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Xiangyun started to work as a PhD in the railway engineering section at Delft University of Technology in 2010. He received his MSc degree in Engineering Mechanics from the Department of Modern Mechanics at University of Science and Technology of China in 2010. His Master research topic was on the mechanical behavior of brittle material under impact loading. Currently, his research interests are rolling contact mechanics and rolling contact fatigue.

- Rolling contact mechanicsrn- Wearrn- Analysis of mechanical behavior of steel under rolling contact loadingrn- Rolling contact fatigue and fracture mechanicsrn 

Numerical Investigation of squats damage under rail/wheel contact

Squats are surface initiated rolling contact fatigue (RCF) defects in the running band of rails in the railway infrastructure, as reported in the literatures since the 1950s. Generally speaking, a mature squat includes two cracks, a leading one that propagates in the rolling direction, and a trailing one that propagates in the opposite direction. The main issue for squats is that cracks can grow downward in the rail. A possible consequence is a broken rail and thus derailment. Considering the effects of vehicle-track dynamic interaction on RCF phenomenon, based on the numerical simulations and the field observations, it is found that the development of a squat is closely related to the dynamic contact force. The contact force is excited by the squat seeds and is determined by the local eigen characteristics of the vehicle-track system. The impact loads can cause large plastic deformation around the middle ridge. This results in the crack initiation. The above work reveals the squat growth process and the wave pattern that often follows squats. Following the previous work, this project combines the examination of measurements and numerical modelling. First, the development of single squats and multi squats are examined in field observations. Also, the profiles of the rail with the squats are measured for simulation. After this, a three dimensional dynamic finite element (FE) model is used to investigate the contact stresses and strains states at around squats. According to the stresses and strains states, the damage produced by plastic deformation, the remaining life of the rail and the cracks initiation at squats are analysed. Furthermore, the results of simulation are compared with the examination of measurements and metallographic observation. The results of this study give an understanding of the mechanism of the squats damage and some influential parameters. The purpose is to help reduce the damage produced by rail squats and to help plan the maintenance of the rail efficiently.

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Xiangyun Deng, MSc

PhD Researcher

+31 (0) 15 278 40 08
X.Deng@tudelft.nl
Building: 23, room 1.54

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