Keywords: derailment, fatigue, casting void, axle, failure analysis, finite element modelling, stress analysis.

On December 30, 2013, a westbound BNSF grain train derailed west of the city of Casselton, ND, causing one of the cars from the derailment to obstruct the opposite track. An eastbound BNSF petroleum crude oil train collided with the fouled car, derailing the locomotives and twenty full tank cars. This accident resulted in the release of more than 400,000 gallons of crude oil, which subsequently ignited and created a large pool fire. One of the axle wheelsets on the fouled grain car was found fractured on the accident scene. When examined by the NTSB Materials Laboratory, the fracture surface of the axle was found to exhibit a large fatigue crack. The fatigue fracture had propagated from a void in the centre of the axle, which was consistent with a solidification void. This paper will detail the failure analysis and characterization of the fractured axle, including how improper manufacturing and ineffective inspection of the axle led to the accident. In addition, the finite element modelling and stress analyses were performed to determine that the area on the void exhibited stress concentrations high enough to initiate fatigue, corresponding with the actual crack initiation sites. Promoting the completion of rail safety initiatives, such as tank car safety, is currently a critical area of focus for the NTSB and is on the agency’s 2016 Most Wanted List.

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