Improving the Quality and Reliability of Large Truck Castings

Recent failures of large freight car castings have resulted in a comprehensive review of the specifications governing the manufacture, inspection, and repair of these steel castings. As part of an overall industry effort to improve the quality and reliability of large freight car castings, the Transportation Technology Center, Inc. (TTCI) conducted finite element and fatigue analyses of the S-2-HD bolster and side frame. The objective of this project is to improve the capacity and safety of train operations by reducing the number of in-service failures of bolsters and side frames. To meet the objective, a total of six S-2-HD bolster and side frame castings from different manufacturers were modeled to estimate the fatigue life of each of the components with and without defects. The results from the finite element analysis were combined with load/stress environment data and mechanical test data to predict the fatigue life of each of the components. The fatigue life analysis covered a variety of defect and no defect conditions and used a strain-life based approach. All of the fatigue estimates are based on life until crack initiation and compared to a target life of 1.5-million loaded miles. Results from the analysis show that few combinations of casting design and defect type/size offer sufficient fatigue strength to reach a target life of the desired 1.5-million loaded miles. The analyses also indicate that a reduction in component stress is necessary to improve the overall fatigue performance of the S-2-HD bolster and side frame castings when defects are present in critical stress areas. To reduce the number of derailments associated with truck castings, improvements in component design, manufacturing processes, and materials are necessary. Implementation of changes in design and materials has the potential to reduce stress in critical areas and increase fatigue life performance when defects are present. In addition, it is critical to develop inspection methods capable of reliably detecting defects to prevent in-service failures. If the aforementioned changes are implemented successfully, there is a potential of reducing in-service failures of truck castings by approximately 30 percent. This paper presents the approach and results of the bolster analysis and gives a brief summary of the results of the side frame analysis.