PSI - Issue 37

Junpeng Li et al. / Procedia Structural Integrity 37 (2022) 582–589 Junpeng Li/ Structural Integrity Procedia 00 (2021) 000 – 000

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transportation density, rail damage has become more and more serious, especially the problems of rail rolling contact fatigue and wear (Yang Yun, 2019), which are important for rail rolling contact fatigue crack initiation and wear development. Research helps to provide guidance and basis for rail material selection, maintenance and repair. The rolling contact fatigue crack of rail is the result of plastic deformation and low cycle fatigue or ratchet effect when the metal material exceeds its shakedown limit under the repeated action of wheel-rail contact stress (Magel E E, 2011). The shakedown limit theory (multi-axial fatigue failure or ratchet failure) is commonly used to explain the initiation of rail fatigue crack. For example, equal effect variation method, critical plane method, energy density method and the combination of the latter two methods (Wang Shaofeng, et al, 2014); In addition, fatigue parameters and fatigue life prediction methods based on strain field are also applied to the prediction of rail fatigue damage (Lu C et al, 2018). The forms of rail wear include abrasive wear, adhesive wear, corrosion wear and surface fatigue wear (Valentin L, Popov, 2011). At present, the energy consumed at the wheel-rail contact spot is commonly used to explain wear, such as Archard wear theory (Archard J.F., 1980) and wear index model (MC Burstow, 2004). In addition, experimental methods are also used to study the law of wear, such as double-disc rolling experiment (Ramalho A, 2015, Iwnicki S D, 2009), etc. However, in the above studies, rail fatigue crack and wear are considered independently, and there is a lack of theoretical explanation of their mutual relationship and quantitative description of the effects of influencing factors. In practice, the crack will lead to the fracture of the surface material and its detachment from the base material, resulting in fatigue wear (Li Z L, 1998). When the wear resistance of the rail is poor, the metal around the crack will be worn off, so that the crack is eliminated or suppressed. On the contrary, cracks remain in the surface material of the rail. Therefore, fatigue crack and wear influence each other in the coexistence and development (Fletcher D I, 2008.), which are influenced by rail material properties, initial state of rail, load, wheel-rail geometric relationship, wheel-rail contact, rail grinding and lubrication, friction control, track geometric parameters and system stiffness and other factors (B. Nielsen, et. al, 2016). The coexisting prediction method of rail crack initiation and wear (ZHOU Yu, et al, 2019) has been used in the prediction of subway rail crack initiation (WU Qiang, 2017). Existing studies can only compare the prediction results with the range of crack initiation life observed in the field, and there is still a lack of experimental verification. In summary, a lot of studies declared that RCF crack initiation and wear are a continuous process of coexistence influence by each other. However, due to the complexity of RCF crack initiation mechanism, the theoretical prediction is also difficult to verify the correlation between fatigue crack and wear development, therefore, the prediction of crack initiation life and wear need to be supplemented and verified by experiments. In this paper, a twin-roller fatigue test rig was used to reproduce the process of the coexistence of fatigue crack initiation and wear growth in the specimens from rail specimens. Based on the test rig situation, a prediction model was established according to the prediction method for coexistence of crack initiation and wear growth in rail. Both the results, including wear, crack initiation position and crack length in the specimens by the test and simulation were analyzed for verifying prediction model. The surface microscopic characteristics of the specimens were also analyzed by electron microscope observation under different number of cyclic loads. 2. Material and Methods A twin-roller fatigue test rig was used to reproduce the process of the coexistence of fatigue crack initiation and wear growth of in the specimens from rail specimens. Meanwhile, with the test rig situation, a prediction model for predicting crack initiation and wear growth in the test specimens was established according to the prediction method for coexistence of crack initiation and wear growth in rail according to the theory of archard wear and critical plane. Therefore, it can compare the test and prediction results in order to verify and evaluate the prediction method for coexistence of the crack initiation and wear growth. The prediction method for the coexistence of crack initiation and wear growth in the rail (Zhou Y, et al, 2016) divides the continuous process of fatigue damage and wear in the rail into finite discrete fatigue – wear growth processes. The entire process of fatigue crack initiation and wear can be described as a process of fatigue damage by variable amplitude load caused by wear growth and profile evolution. For validating the method, on one hand, a series of tests were design an experiment by small-scale twin-roller fatigue test rig with specimens from rail specimens in which the test parameters can be designed according to the wheel-rail contact situation and the process of fatigue damage and wear can be observed carefully. On the other hand,