Fatigue Strength Evaluation of the Aluminum Carbody of Urban Transit Unit by Large Scale Dynamic Load Test

Aluminum carbody for rolling stock is light and easily recycled, but includes severe defects which are very dangerous to fatigue strength. Strength evaluation of a carbody by static load test has been performed. However, true evaluation of fatigue strength could not be performed because fatigue failure is caused by dynamic alternating loads. In this study, to evaluate fatigue strength of the aluminum carbody of urban transit unit, a large scale testing method to simulate actual dynamic loads is proposed and the fatigue failures of the carbody are investigated. The test results are compared with the estimated results by static load test and structural analysis. Also, the differences between the results are discussed. The compared results show that flexural response of the carbody plays a significant role in occurrence of fatigue failure. The estimation of fatigue failure based on static load test or static analysis may provide misleading results. It was also verified that the fatigue life characteristics of the aluminum carbody can be estimated from the published fatigue test data for aluminum components with similar joint detail. Test and evaluation of fatigue strength based on the established static load test method needs to be modified to consider dynamic response of the carbody.