Raking Impact of a Diesel Multiple Unit Fuel Tank: Results of Test No. 2 and Analysis
Authors: Jacobsen Karina , Carolan Michael 
Published: June 2021

The Federal Railroad Administration (FRA) sponsors research on safety topics to address and to improve safety regulations and standards. This paper is part of a series of papers that describe the testing and analysis used to evaluate passenger locomotive fuel tank integrity. Fuel tank integrity federal regulations, as well as industry standards, currently exist in the form of a series of static load conditions. The static load conditions are a set of prescribed loads on all passenger fuel tanks, which set a minimum level of protection against impacts that might puncture the tank and cause the release of diesel fuel. If diesel fuel is ignited in an impact incident, collision or derailment, the crew and passengers may be at risk. In the current research program a series of dynamic impact tests and quasi-static tests were conducted that measure the forces required to deform a fuel tank and investigate the types of loading conditions experienced by fuel tanks.

The objective of the testing program is to establish the baseline puncture resistance of current locomotive fuel tanks under dynamic impact conditions and to develop performance requirements for an appropriate level of puncture resistance in alternative fuel tank designs, such as Diesel Multiple Unit (DMU) fuel tanks. The tests were divided into two loading scenarios identified from accidents: blunt impact and raking impact.

In the most recent phase of testing, DMU fuel tanks were tested in a test setup that quasi-statically loaded the side and bottom of the fuel tanks. Conducted in December 2018 and November 2019, these tests were designed to simulate a raking impact scenario of a fuel tank. The Transportation Technology Center Inc. (TTCI), with support from the Volpe Center designed a test setup using a fuel tank mounted to a boxcar placed within the “squeeze frame”. An indenter, shaped like a broken rail, is fixed to the ground and the fuel tank is slowly pushed into the indenter using a series of hydraulic rams. Load cells and string potentiometers are used to measure the force/displacement. Cameras capture the deformation profile of the fuel tank. The Volpe Center develops and performs finite element analysis to evaluate the loading scenario prior to testing.

In this paper, the results of the second raking test are described. A companion paper, previously published, presented the results of the first raking test. During the second raking test, the indenter was aligned beneath the bottom surface of fuel tank. The fuel tank, mounted to a boxcar, was pushed toward the indenter. Due to the downward sloping surface of the fuel tank, the indenter, maintained at a constant vertical height, began to contact the fuel tank bottom surface and push into the surface as it was advanced a total of 42 inches. The results of pre-test analyses for the second raking impact test are presented to highlight the critical position on the impacted fuel tank. The analysis gives an estimate of the force required to puncture the fuel tank as well as the resultant tear of the fuel tank.

These results highlight the detailed differences of quasi-static versus dynamic loading of fuel tanks, which supports defining trade-offs between specifying static load requirements versus scenario-defined performance based standards. The development of and results from the finite element model show the uses and limitations of the finite element models in understanding material failure. The results may be used by industry to better understand how design choices can influence fuel tank integrity against impacts and also guide standard development of less prescriptive load requirements that still uphold equivalent safety requirements as the existing standards.