Abstract During the space shuttle return-to-flight preparations following the Columbia accident, finite element models were needed that could predict the threshold of critical damage to the orbiter’s wing leading edge from ice debris impacts. Hence, an experimental program was initiated to provide crushing data from impacted ice for use in dynamic finite element material models. A high-speed drop tower was configured to capture force time-histories of ice cylinders for impacts up to approximately 100 ft/s. At low velocity, the force-time history depended heavily on the internal crystalline structure of the ice. However, for velocities of 100 ft/s and above, the ice fractured on impact, behaved more like a fluid, and the subsequent force-time history curves were much less dependent on the internal crystalline structure. Background In Chapter 11 of the Columbia Accident Investigation Board (CAIB) report [1], which was released after the space shuttle Columbia Accident, recommendation 3.3-2 requested that NASA initiate a program to improve the impact resistance of the shuttle orbiter wing leading edge. The second part of the recommendation was …“determine the actual impact resistance of current materials and the effect of likely debris strikes.” In addition, recommendation 3.8.2 states, “Develop, validate, and maintain physics-based computer models to evaluate Thermal Protection System (TPS) damage from debris impacts. These tools should provide realistic and timely estimates of any impact damage from possible debris from any source that may ultimately impact the Orbiter. Establish impact damage thresholds that trigger responsive correction action, such as on-orbit inspection and repair, when indicated. ” Consequently, to comply with the spirit of the CAIB recommendations, a team from NASA Glenn Research Center (GRC), NASA Langley Research Center (LaRC), and Boeing was given the following task: to develop a validated finite-element model of the Orbiter wing leading edge capable of accurately predicting the threshold of critical damage from debris including foam, ice, and ablators for a variety of impact conditions. Since the CAIB report was released, the team has been developing LS-DYNA models of the reinforced carbon-carbon (RCC) leading edge panels, conducting detailed material characterization tests to obtain dynamic material property data for RCC and debris, and correlating the LS-DYNA models with data obtained from impacts tests for both small-scale flat panels and full-size RCC flight hardware panels [2-6]. Foam impacts onto RCC panels were examined first. Once the RCC thresholds for foam impacts were determined, attention was directed to ice debris.
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