Publications

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The increased demand for Liquefied Natural Gas (LNG) as a fuel source in the U.S. has prompted a study to improve our capability to predict cascading damage to LNG tankers from cryogenic spills and subsequent fire. To support this large modeling and simulation effort, a suite of experiments were conducted on two tanker steels, ABS Grade A steel and ABS Grade EH steel. A thorough and complete understanding of the mechanical behavior of the tanker steels was developed that was heretofore unavailable for the span of temperatures of interest encompassing cryogenic to fire temperatures. This was accomplished by conducting several types of experiments, including tension, notched tension and Charpy impact tests at fourteen temperatures over the range of -191 C to 800 C. Several custom fixtures and special techniques were developed for testing at the various temperatures. The experimental techniques developed and the resulting data will be presented, along with a complete description of the material behavior over the temperature span.

Instrumented, fully coupled thermal-mechanical experiments were conducted to provide validation data for finite element simulations of failure in pressurized, high temperature systems. The design and implementation of the experimental methodology is described in another paper of this conference. Experimental coupling was accomplished on tubular 304L stainless steel specimens by mechanical loading imparted by internal pressurization and thermal loading by side radiant heating. Experimental parameters, including temperature and pressurization ramp rates, maximum temperature and pressure, phasing of the thermal and mechanical loading and specimen geometry details were studied. Experiments were conducted to increasing degrees of deformation, up to and including failure. Mechanical characterization experiments of the 304L stainless steel tube material was also completed for development of a thermal elastic-plastic material constitutive model used in the finite element simulations of the validation experiments. The material was characterized in tension at a strain rate of 0.001/s from room temperature to 800 C. The tensile behavior of the tube material was found to differ substantially from 304L bar stock material, with the plasticity characteristics and strain to failure differing at every test temperature.

Coupled thermal-mechanical experiments with well-defined, controlled boundary conditions were designed through an iterative process involving a team of experimentalists, material modelers and computational analysts. First the basic experimental premise was selected: an axisymmetric tubular specimen mechanically loaded by internal pressurization and thermally loaded asymmetrically by side radiant heating. Then several integrated experimental-analytical steps were taken to determine the experimental details. The boundary conditions were mostly thermally driven and were chosen so they could be modeled accurately; the experimental fixtures were designed to ensure that the boundary conditions were met. Preliminary, uncoupled analyses were used to size the specimen diameter, height and thickness with experimental consideration of maximum pressure loads and fixture design. Iterations of analyses and experiments were used to efficiently determine heating parameters including lamp and heating shroud design, set off distance between the lamps and shroud and between the shroud and specimen, obtainable ramp rates, and the number and spatial placement of thermocouples. The design process and the experimental implementation of the final coupled thermomechanical failure experiment design will be presented.

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An interdisciplinary team of scientists and engineers having broad expertise in materials processing and properties, materials characterization, and computational mechanics was assembled to develop science-based modeling/simulation technology to design and reproducibly manufacture high performance and reliable, complex microelectronics and microsystems. The team's efforts focused on defining and developing a science-based infrastructure to enable predictive compaction, sintering, stress, and thermomechanical modeling in ''real systems'', including: (1) developing techniques to and determining materials properties and constitutive behavior required for modeling; (2) developing new, improved/updated models and modeling capabilities, (3) ensuring that models are representative of the physical phenomena being simulated; and (4) assessing existing modeling capabilities to identify advances necessary to facilitate the practical application of Sandia's predictive modeling technology.

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