Publications

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In order to predict blast damage on structures, it is current industry practice to decouple shock calculations from computational structural dynamics calculations. Pressure-time histories from experimental tests were used to assess computational models developed using a shock physics code (CTH) and a structural dynamics code (PRONTO3D). CTH was shown to be able to reproduce three independent characteristics of a blast wave: arrival time, peak overpressure, and decay time. Excellent agreement was achieved for early times, where the rigid wall assumptions used in the model analysis were valid. A one-way coupling was performed for this blast-structure interaction problem by taking the pressure-time history from the shock physics simulation and applying it to the structure at the corresponding locations in the PRONTO3D simulation to capture the structural deformation. In general, the one-way coupling was shown to be a cost-effective means of predicting the structural response when the time duration of the load was less than the response time of the structure. Therefore, the computational models were successfully evaluated for the internal blast problems studied herein.

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This paper describes the analyses and the experimental mechanics program to support the National Aeronautics and Space Administration (NASA) investigation of the Shuttle Columbia accident. A synergism of the analysis and experimental effort is required to insure that the final analysis is valid - the experimental program provides both the material behavior and a basis for validation, while the analysis is required to insure the experimental effort provides behavior in the correct loading regime. Preliminary scoping calculations of foam impact onto the Shuttle Columbia's wing leading edge determined if enough energy was available to damage the leading edge panel. These analyses also determined the strain-rate regimes for various materials to provide the material test conditions. Experimental testing of the reinforced carbon-carbon wing panels then proceeded to provide the material behavior in a variety of configurations and strain-rates for flown or conditioned samples of the material. After determination of the important failure mechanisms of the material, validation experiments were designed to provide a basis of comparison for the analytical effort. Using this basis, the final analyses were used for test configuration, instrumentation location, and calibration definition in support of full-scale testing of the panels in June 2003. These tests subsequently confirmed the accident cause.