United States Department of Transportation
i
Damage Assessment of Railroad Tank Cars Involved in Accidents Phase II, Modeling and Validation
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2002-12-01
[PDF-3.68 MB]
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TRIS Online Accession Number:00940830
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Edition:Final Report
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Abstract:The Accident Damage Assessment Guidelines used to make decisions on the safety of damage pressure tank cars were formulated in the 1970s by the Association of American Railroads (AAR) under the auspices of the Federal Railroad Administration. Although these Guidelines have served their purpose, their validity has not been quantitatively established. This report describes an effort by the Association of American Railroads/Transportation Technology Center, Inc. (AAR/TTCI) and SRI International to examine and refine the Guidelines. Damage mechanics was applied to evaluate the effect of gouges and wheel burns. Notched round bar tensile tests were combined with finite element analysis to predict cleavage failure in the absence of a macroscopic crack. Fracture mechanics was applied to evaluate the stability of a thumbnail crack at a dent root and through-wall crack. J-resistance tests were used to support the analysis. Laboratory dent/undent tests in which plate was bent then pulled straight in tension were applied to evaluate the effects of denting. The research showed that the present Guidelines are valid, with reasonable factors-of-safety, except for otherwise-undamaged dents that do not involve welds. Consideration of dent root radius should be removed from the Guidelines because radius has little bearing on the likelihood of failure. Tank pressures above about 100 psi are sufficient to straighten longitudinal dents and leave them with large root radii. Accordingly, the largest root radii have seen the highest pressures and the most deformation, yet previously were considered the safest. Fortunately, the dent/undent tests showed that otherwise-undamaged dents that do not involve welds fail at loads equal to those for virgin plate. The crack stability analysis and toughness measurements showed that through-wall cracks are stable up to at least several inches in length. Thumbnail dent root cracks are likely to be unstable and can grow readily to be as long as the dent. Thus, the risk of dent failure depends on the likelihood of a dent containing a crack. The research shows that the likelihood is very low unless the dent involves other damage or welds.
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