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For the past two decades, the Federal Railroad Administration (FRA) Office of Research and Development has sponsored research conducted by the Volpe National Transportation Systems Center (Volpe Center) in safety matters related to the transportation of hazardous materials by railroad tank cars. Recent research conducted by the Volpe Center has included the application of semi-empirical and computational (i.e., finite element analysis) methods to estimate the puncture resistance of conventional railroad tank cars under generalized head and shell impact scenarios. Subsequent work identified sandwich structures as a potential technology to improve the puncture resistance of the commodity-carrying tank under impact loading conditions. This paper summarizes basic research (i.e., testing and analysis) conducted to examine the deformation behavior of flat-welded steel sandwich panels under two types of quasi-static loading: (1) uniaxial compression; and (2) bending through an indenter. The objectives of these tests were to: (1) confirm the analytical and computational (i.e., finite element) modeling of sandwich structures, (2) examine the fabrication issues associated with such structures (e.g., material selection and welding processes), and (3) observe the deformation behavior and local collapse mechanisms under the two different types of loading. In addition, the uniaxial compression tests were performed to rank or screen different core geometries. Five core geometries were examined in the compression tests: pipe or tubular cores with outer diameters equal to 2, 3, and 5 inches; a 2-inch square diamond core; and a double-corrugated core called an X-core with a 5-inch core height. The compression tests showed excellent repeatability of structural (i.e., force-crush) response for panels with similar cores and welding. The 3-inch pipe core and the diamond core were selected as candidate cores for the next test series because they possess attributes of moderate strength and moderate relative density. In addition, force-crush curves calculated from finite element analysis were in reasonable agreement with the measured curves for all cores. Bend tests using a 12-inch by 12-inch indenter with 1-inch radius rounded edges were also conducted. The panels were simply-supported over 4-inch diameter rollers spanning 24 inches between the centers of the rollers. The bend tests included three variables: (1) core type (diamond core and 3-inch pipe core); (2) core orientation relative to the supports (cores running either parallel or perpendicular to the rollers used to support the panels); and (3) face sheet type (solid plates on both sides, strips used as face sheets on both sides, and a combination of solid plates and strips. Finite element analysis of the bend tests produced nearly identical shapes to the measured force-displacement curves.Copyright © 2011 by ASME |
