Reliability Evaluation and Life Prediction for Railway Safety Parts

Abstract

With an increase of the interest in product reliability, manufacturers are increasingly in need of product reliability assessment. Reliability analysis and evaluation methods are widely known by using relevant specifications, standards, and data books. The failure rate of each unit of hardware is predicted based on the relevant criteria, and the mean life time and failure rate of the system are calculated in order to analyze and evaluate the reliability of the entire system. However, even in the same product, the life suggested by the manufacturer may vary depending on the usage environment. Therefore, it is important that the product is used in a stressful environment. This brings about the need of a thorough analysis of the use environment and the evaluation of the optimal life of the product considering the stress in the environment. Based on the results of this evaluation, the optimal replacement cycle should be determined. In this thesis, we studied approaching the platform safety step system and the railway vehicle contactor from two perspectives which is reliability evaluation and life prediction. There are three main topics in this paper. The first, we reviewed the method of reliability evaluation using the specifications, standards and data books in the development of the platform safety step system. It is necessary to supplement the reliability evaluation of the entire system because there are limitations in assessing the reliability of the system using only relevant standards and data books. Therefore, as a supplementary method, FMECA (Failure Modes, Effects and Criticality Analysis) and Hazard analysis were performed to supplement the reliability evaluation of the entire system-based parts. Finite element analysis was run to confirm the structural safety of the entire system, and the physical impact test was performed for fail safety assurance with high speed camera. Also the durability test evaluation technique using the NFTT (No Failure Test Time) was proposed. Appendix 1 describes the reliability analysis results of the platform safety step system using the standard, data books including EPRD, NPRD and analyzing RBD, FTA techniques after hierarchical classification of each module and parts constituting the platform safety step system. Second, acceleration stress is selected for railway vehicle contactors, which are the major parts of railway vehicles, and accelerated life tests are performed to estimate related parameters based on reliability analysis using failure data obtained through real-time monitoring system. The estimated parameters are then used to predict mean life and percentile life under normal use conditions. Third, using the estimated parameters derived from the failure data analysis of the railway vehicle contactor acquired through accelerated life test and applying the age replacement policy considering maintenance cost information and the cost incurred in the failure, the optimal replacement cycle is proposed to minimize the opportunity cost per unit time considering the costs incurred during the maintenance and preventive maintenance replacement.

Keywords : Reliability evaluation, Life prediction, Accelerated life test, Optimal replacement cycle, Railway safety parts