Thermal and Structural Response Modeling of a Woven Thermal Protection System

Abstract

NASA’s future missions include destinations such as Venus, Saturn, and Jupiter, where the heat-intensive environments experienced during atmospheric entry by vehicles or probes often exceed the capability of conventional Thermal Protection System (TPS) materials (e.g., Phenolic Impregnated Carbon Ablator (PICA), Heritage Carbon Phenolic (HCP)). The Woven Thermal Protection System (WTPS), a relatively new concept of ablative TPS design, has been of key interest in the past decade to replace heritage materials. In the design of TPS, characterizing the material’s thermal and structural performance is critical. The focus of this dissertation is on improving the modeling of WTPS, in particular, the Heatshield for Extreme Entry Environment Technology (HEEET), a dual layer WTPS composed of an outer recession-resistant layer and inner insulative layer. The results focus on three aspects. The first aspect is focused on pure thermal response modeling of HEEET in a radiant heating facility. The simulation results are compared to experimental measurements, and improved material and boundary condition models are derived based on the analyses. xi The second aspect is focused on pure structural response modeling of the 24 in. HEEET weave under four point bend mechanical loading. The model is assessed using experimental measurements. Initial simulations are performed using stiffness properties derived from a smaller HEEET weave at room temperature. Comparisons between the experimental measurements and simulation results for deformation indicate that the 24 in. recession layer is 130% stiffer than the smaller weave. The last aspect is focused on coupled thermo-structural response modeling of HEEET subject to combined mechanical and thermal loading. Discrepancies between simulation predictions and experimental measurements of deformation suggest that significant stiffness degradation is occurring. The subsequent stiffness degradation studies indicate that the stiffness of HEEET is monotonically decreasing in the temperature range being modeled. When using the inferred stiffness reduction factors for coupled thermo-structural modeling, the predictions for strain are in much closer agreement with experimental measurements. Limitations of the studies are discussed, which motivate the need for higher-fidelity experimental tests that can be used to deduce improved models.