Research on Quantitative Evaluation Method of Rolling Contact Fatigue Damage Based on Wedge Volume or Cross-sectional Area of ​​Crack Damage

With the rapid development of Chinese railway transport, especially with increasing wheel-rail contact interaction is enhanced and thus the daily operation and maintenance of the wheel-rail system are facing new technical challenges. Furthermore, the wheel-rail rolling contact fatigue (RCF) damage problem has become the focus and difficulty in the research of wheel-rail contact behaviors. Aiming at the different forms of RCF cracks, the crack damage can be effectively evaluated by quantitative evaluation of fatigue cracks with reasonable evaluation methods, which can provide theoretical guidance for the maintenance of rolling elements. This work taken wheel-rail RCF crack damage as a special case. A method for confirming the minimum crack size limit for the objective evaluation of RCF damage of different wheel and rail materials was first proposed, then a quantitative evaluation method for RCF crack damage value was further constructed based on the wheel-rail RCF crack damage characteristics. Firstly, based on the microstructure grain size of different wheel and rail materials, a method for determining the minimum crack length for the objective evaluation of RCF damage of wheel and rail materials was established. Secondly, a quantitative evaluation method for RCF crack damage was further constructed based on the wedge volume or cross-sectional area of wheel-rail RCF crack damage. Finally, according to the contact parameters for the ratchetting could occur in the engineering application-oriented shakedown map, wheel-rail RCF simulation tests under different contact parameters were carried out. According to the minimum crack length standard for the objective evaluation of RCF damage, the fatigue cracks of rail material were systematically analyzed using commonly used quantitative evaluation indices of fatigue cracks. Meanwhile, the fatigue crack damage of rail material was quantitatively evaluated by the novel quantitative evaluation method, and the evaluation effects of other quantitative evaluation methods on crack damage were compared and analyzed. Then, a comparison of different evaluation results was performed. The results showed that the minimum crack size limit for the objective evaluation of wheel-rail RCF damage could be reasonably confirmed from the microstructure grain size of wheel and rail materials, which could reasonably determine the crack size for objectively evaluating RCF damage of different materials. The novel quantitative evaluation method based on the wedge volume or cross-sectional area of crack damage could be used to quantitatively evaluate the RCF crack damage, and the evaluation result was consistent with that of the quantitative evaluation through a single evaluation index of RCF cracks and other current quantitative evaluation methods. Moreover, the quantitative evaluation method established in this paper comprehensively considered two important behaviors of RCF damage cracks: lateral extension on the wheel-rail contact surface and extensions within the materials. This new evaluation method included all evaluation indicators of crack size, namely crack length, depth and extension angle. This new evaluation method also had a clear physical meaning, namely the wedge volume/cross-sectional area of the damaged materials. In this work, a method for confirming the crack size for objectively evaluating RCF damage of different materials based on the microstructure grain size of materials was developed, and the quantitative evaluation method for the RCF crack damage of different materials was initially constructed. This novel method was applicable to the quantitative evaluation for RCF crack damage of different rolling elements.