The Influence of Model Complexity on the Impact Response of a Shuttle Leading-Edge Panel Finite Element Simulation

Abstract LS-DYNA simulations were conducted to study the influence of modelcomplexity on the response of a typical Reinforced Carbon-Carbon(RCC) panel to a foam impact at a location approximately midwaybetween the ribs. A structural model comprised of Panels 10, 11, and T-Seal 11 was chosen as the baseline model for the study. A simulationwas conducted with foam striking Panel 10 at Location 4 at an alphaangle of 10 degrees, with an impact velocity of 1000 ft/sec. A secondsimulation was conducted after removing Panel 11 from the model, and athird simulation was conducted after removing both Panel 11 and T-Seal11. All three simulations showed approximately the same response forPanel 10, and the simplified simulation model containing only Panel 10was shown to be significantly less expensive to execute than the othertwo more complex models. Introduction Following the Space Shuttle Columbia disaster on February 1, 2003 and during the subsequentinvestigation by the Columbia Accident Investigation Board (CAIB), various teams from industry,academia, national laboratories, and NASA were requested by Johnson Space Center (JSC) OrbiterEngineering to apply “physics-based” analyses to characterize the expected damage to the shuttle thermalprotection system (TPS) tile and Reinforced Carbon-Carbon (RCC) material, for high-speed foamimpacts. The forensic evidence from the Columbia debris eventually led investigators to conclude thatthe breach to the shuttle TPS was caused by a large piece of External Tank (ET) foam that impacted andpenetrated the lower portion of a left-wing leading-edge panel. As a result, NASA authorized a series oftests that were performed at Southwest Research Institute to characterize the impact response of theleading-edge RCC panels.Recommendation 3.3-2 of the CAIB report [1] requests that NASA initiate a program to improve theimpact resistance of the wing leading edge. The second part of the recommendation was to …“determinethe 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 Glenn Research Center, NASA LangleyResearch Center, and Boeing Philadelphia was given the following task: to develop a validated finiteelement model of the shuttle wing leading edge capable of accurately predicting the threshold of damagefrom debris including foam, ice, and ablators for a variety of impact conditions. Since the CAIB reportwas released, the team has been developing finite element models of the RCC leading-edge panels;executing the models using LS-DYNA [2], a commercial nonlinear explicit transient dynamic finiteelement code; conducting detailed material characterization tests to obtain dynamic material propertydata; and, correlating the LS-DYNA analytical results with experimental data obtained from impacts testsonto RCC panels. Some of the early results of this research are described in References 3-7.The purpose of this report is to describe LS-DYNA simulations that were conducted to study theinfluence of model complexity on the response of a typical RCC panel to a foam impact at a locationapproximately midway between the ribs. A structural model comprised of Panels 10, 11, and T-Seal 11(see Figure 1) was chosen as the baseline model for the study. A simulation was conducted with foam