Method of identification of the ranges of (non)acceptable factor values to reduce the risk of freight car derailment due to broken bogie solebar

Abstract

Aim. According to the Russian freight car crash/derailment investigation records for the period between 2013 and 2016., derailments and crashes during train operations were mostly caused by rolling stock malfunctions, while about a third of such derailments were due to bogie solebar fracture. The average number of derailed units of rolling stock is 4.16 in case of derailment due to solebar fracture against 1.73 in case of derailments due to other rolling stock malfunctions. Previously, a method was developed that allows making decisions to discard a batch of solebars. On the other hand, solebars from batches exempt from discarding can be subject to fractures over time. In this context, it appears to be of relevance to develop a method that would enable timely uncoupling of a car for its submission to depot/full repairs in order to avoid solebar fracture. For this purpose, factor models of fracture hazard estimation should be considered. Such factors may include the number of kilometers travelled from the last maintenance depot (MD), as well as the number of kilometers and days until the next scheduled full/depot repairs. The probability of solebar fracture can be used as the quantitative characteristic of the hazard of solebar fracture. However, probability estimation in the form of, for instance, the frequency of solebar fracture is only possible when observation data is available on when fracture or critical defect of solebar did not occur, yet such data is not collected. Therefore, the hazard index of solebar fracture should be developed. As it is difficult to manage the frequency of car submission to MD, the hazard index must depend only on the number of days and kilometers to repairs. Using the constructed index, the ranges of (non) acceptable factor values must be defined in order to enable decision-making regarding car uncoupling and submission to repairs, should the MD car inspector have doubts regarding the necessity of uncoupling. Methods. Methods of mathematical programming were used in this paper. Results. Conclusions. An impact index was built that characterizes the probability of freight car solebar fracture depending on the number of days and kilometers until the next scheduled repairs of such car. Based on that index, two methods of definition of ranges of (non)acceptable factor values were proposed. The first method was based on the values of the impact index. The second one was based on the identification of some parameters of ranges of (non)acceptable factor values and selection – out of all ranges – of the best ones in terms the lowest hazard of solebar fracture. Such selection was made by solving problems of mixed integer programming with quadratic constraint.