# Influence of Fastener Failure on Dynamic Performance of Subway Vehicle
## 4 Conclusions  
After a long period of operation, the subway track structure may be damaged. The vehicle-subway track system model was established with the goal of evaluating the influence caused by fastener failure. The model's calculation results are verified for accuracy, and the dynamic responses of the track structure and vehicle running performance under different numbers of fastener failures are compared using time history responses. Finally, the vehicle's running comfort and safety are investigated at various speeds while passing through various fastener failures, and the following conclusions can be obtained:  
1. Through the comparison of time history response, it is found that the impact of fastener failure on the structural response is greater than that of vehicle response. Among them, the structural displacement response is more sensitive to structural failure than the acceleration response.
2. At different vehicle speeds, the number of fastener failures has little effect on the acceleration response of vehicle operation.
3. At different vehicle speeds, the number of fastener failures has an impact on the Nadal index of the vehicle, but the law is not obvious. In general, the more fastener failures, the more unsafe it is.
4. Under different vehicle speeds, the number of fastener failures has a significant impact on the wheel load reduction rate of the vehicle, and the wheel load reduction rate increases with the increase in vehicle speed and with the increase in the number of fastener failures. For the engineering background, when only less than three fasteners fail, the vehicle can run safely at the design speed; when four fasteners fail, the safe allowable speed of the vehicle is 130 km/h; when five fasteners fail, the safe allowable speed of the vehicle is 80 km/h.
5. The vehicle acceleration is not sensitive to the failure of the fastener but the failure of the fastener may endanger the running safety so it is necessary to use manual or other technical means for regular detection of fasteners. According to the normal vehicle operation speed, it is suggested that when more than three continuous fasteners are likely to fail or have become loose, they must be maintained.  
Conceptualization, Y.F.; Funding acquisition, Y.F.; Investigation, T.Z.; Project administration, Y.F.; Software, X.L.; Validation, Y.Y.; Writing--original draft, J.L.; Writing--review & editing, Y.Y. and X.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research is jointly supported by the Research Project of Nanchang Rail Transit Group Co., Ltd.,(JS-2021-3A-ZG-A-ZX-001), the State Key Laboratory of Performance Monitoring and Protecting of Rail Transit Infrastructure (HJGZ20212009) and Fujian University of Technology (GY-Z21181), Science and Technology Project of Department of Transportation of Jiangxi Provincial (2019Q0024). The above support is greatly appreciated.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data used to support the findings of this study are included within the article.  
**Conflicts of Interest:** The authors declare no conflict of interest.