An Evaluation of Derailment Mechanics and Derailment Analysis Methodologies

Detailed analyses of vehicle and train collisions are a common part of new vehicle design projects. It is relatively simple to describe appropriate collision scenarios for a train and the resulting collision mechanics are reasonably controlled if the trains remain upright and in-line. These scenarios are well suited to advanced dynamic finite element simulation codes. Alternatively, train derailment analyses are less common and have unique characteristics that make the analyses difficult. The derailment event can involve the interaction of many cars and have a relatively long duration compared to other crash events. Freight derailments can involve trains in excess of 100 cars long and the duration of the derailment response can be on the order of a minute before coming to rest. Further complicating the analysis are the many parameters that are not well characterized or controlled. The motions of rail cars after leaving the tracks are not well known and difficult to model. The wheels and trucks can plough through ground or remaining track sections. The material properties and geometry of the ground can have large variations and are typically not well known or characterized for specific derailment events. Additionally, the geometry of the surrounding terrain can have a wide range of variability at derailment sites. As a result of these complexities, there are far fewer standardized methodologies used for the analysis of derailments. The detailed finite element models are applied in some cases, but the computational requirements to model these events in high fidelity are quite high. This paper provides a review of some past derailment modeling efforts and recent investigations and analyses of derailment events to provide insights into the derailment mechanics of freight trains. The objective is to assess the relative magnitudes of effects such as the braking characteristics, brake application delay time, and blockage force caused by the derailed and overturned cars on the subsequent deceleration of the trailing cars on the rail.