Evaluation of locomotive frame and fuel tank gusset modifications to prevent fatige cracks

Abstract

Fatigue cracks have been detected in the underframes, fuel tanks, and fuel-tank gussets of some diesel locomotives that are currently in service. This presents the risk of a fuel tank separating from its locomotive and has an associated cost for making repeated repairs. It is therefore an interest to both operators of locomotives and to the designers of future locomotive models to understand the root cause of the cracks and to determine an effective remedy. In order to accomplish these goals, a finite element analysis (FEA) was used to identify events in the service environment that are capable of driving crack growth at a frequency that roughly matches the observed interval between crack repairs. These events were then used in further FEA simulations to predict the efficacy of various proposed remedies. It was found that the fuel tank, engine, and alternator of a locomotive behave as structural elements that resist deformations in the underframe. This explains why locomotive models with a relatively large fuel tank when compared to their engine and alternator are particularly susceptible to developing cracks: they experience higher stresses on their fuel tank and supporting brackets. It was also found that the most effective remedies were those that mitigate stress concentration effects from the gusset's rectangular design.