![]() The complete model including the foam projectile and the RCC Panel 6 is shown in Figure 2. Predicted structural deformations and time- history responses are compared for each simulation. The simulations were executed in LS-DYNA for 6 ms. For each simulation, the same material properties and impact conditions were specified and only the mesh density was varied. For the mesh refinement study, nine cases were executed with all possible combinations of coarse, baseline, and fine meshes of the foam and panel. ![]() While the finite element model was originally developed to generate analytical predictions for correlation with experimental data obtained from this test, the focus of the mesh refinement study described in this report is strictly analytical. An actual impact test of a BX-250 foam block onto RCC Panel 6 was performed at Southwest Research Institute on June 5, 2003. The location of Panel 6 on the left wing of the shuttle is highlighted in Figure 1. In particular, the mesh study was focused on simulating a rectangular foam projectile, having the same material properties as the BX-250 foam used on the shuttle ET, impacting the shuttle leading-edge RCC Panel 6 at a velocity of 775 ft/s. The purpose of this report is to describe a mesh refinement study that was performed as part of the ongoing RTF modeling efforts. Some of the early results of this research are described in References 3-7. Since the CAIB report was released, the team has been developing finite element models of the RCC leading-edge panels executing the models using LS-DYNA conducting detailed material characterization tests to obtain dynamic material property data and, correlating the LS-DYNA analytical results with experimental data obtained from impacts tests of RCC panels. Center, NASA Langley Research Center, and Boeing Philadelphia was given the following task: to develop a validated finite element model of the shuttle wing leading edge capable of accurately predicting the threshold of damage from debris including foam, ice, and ablators for a variety of impact conditions. The second part of the recommendation is to “determine the actual impact resistance of current materials and the effect of likely debris strikes.” For Return-to-Flight (RTF), a team consisting of personnel from NASA. Recommendation 3.3-2 of the CAIB report requests that NASA initiate a program to improve the impact resistance of the wing leading edge. As a result, NASA authorized a series of tests that were performed at Southwest Research Institute to characterize the impact response of the leading-edge RCC panels. The forensic evidence from the Columbia debris eventually led investigators to conclude that the breach to the shuttle TPS was caused by a large piece of External Tank (ET) foam that impacted and penetrated the left-wing leading-edge panel, shown in Figure 1. the Space Shuttle Columbia disaster on February 1, 2003, and during the subsequent investigation by the Columbia Accident Investigation Board (CAIB), various teams from industry, academia, national laboratories, and NASA were requested by Johnson Space Center (JSC) Orbiter Engineering to apply “physics-based” analyses to characterize the expected damage to the shuttle thermal protection system (TPS) tile and Reinforced Carbon-Carbon (RCC) material, for high-speed foam impacts.
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