Validation of Puncture Simulations of Railroad Tank Cars Using Full-Scale Impact Test Data

Abstract

The U.S. Department of Transportation’s Federal Railroad Administration (FRA) has sponsored a series of full-scale dynamic shell impact tests to railroad tank cars. Currently, there are no required finite element (FE) model validation criteria or procedures in the field of railroad tank car puncture testing and simulation. Within the shell impact testing program sponsored by FRA, comparisons made between test measurements and simulation results have included the overall force-time or force-indentation histories, the puncture/non-puncture outcomes, the rigid body motions of the tank car, the internal pressures within the lading, and the energy absorbed by the tank during the impact. While qualitative comparisons (e.g. the shapes of the indentation) and quantitative comparisons (e.g. peak impact forces) have been made between tests and simulations, there are currently no requirements or guidelines on which specific behaviors should be compared, or what measurable level of agreement would be acceptable demonstration of model validation. It is desirable that a framework for model validation, including well-defined criteria for comparison, be developed or adopted if simulation is to be used without companion shell impact testing for future tank car development. One of the challenges to developing model validation criteria and procedures for tank car shell puncture is the number of complex behaviors encountered in this problem, and the variety of approaches that could be used in simulating these behaviors. The FE models used to simulate tank car shell impacts include several complex behaviors, each of which can introduce uncertainty into the overall response of the model. These behaviors include dynamic impacts, non-linear steel material behavior, including ductile tearing, two-phase (water and air) fluid-structure interaction, and contact between rigid and deformable bodies. Several candidate qualitative and quantitative comparisons of test measurements and simulations results are discussed in this paper. They are applied to two recently-completed shell impact tests of railroad tank cars sponsored by FRA. For each test, companion FE simulation was performed by the Volpe National Transportation Systems Center. The process of FE model development, including material characterization, is discussed in detail for each FE model. For each test, the test objectives, procedures, and key instrumentation are summarized. For each set of test and simulations, several corresponding results are compared between the test measurements and the simulation results. Additionally, this paper includes discussion of approaches to model validation employed in other industries or areas of transportation where similar modeling aspects have been encountered.