Uncertainty Analysis of Integrated Thermal Protection System with Rigid Insulation Bars

Abstract

Integrated thermal protection systems (ITPS) are multi-functional structures that combine the functions of conventional TPS (heat shields) and load bearing structural panels of a hypersonic vehicle. Because of its complex design, an ITPS panel could fail due to multiple failure modes. This paper focuses on uncertainty characterization and uncertainty in failure prediction of an ITPS. Monte Carlo simulation is one of the ways to predict uncertainty in failure. Previous work suggests that the Separable Monte Carlo method (SMC) would efficiently handle multiple failure modes in predicting probability of failure. SMC takes advantage of statistical independence of limit state random variables of the response and capacity to provide an accurate estimate. In this paper the ITPS is analyzed under thermal load (heat flux) which is one of the critical loads during reentry of hypersonic vehicles. The ITPS geometry parameters are initially optimized deterministically for minimum mass. Under thermal loads an ITPS could fail due to excessive face sheet temperature, stresses, or buckling. Hence, the face sheet temperature, stresses and buckling loads are used as constraints. These constraints are also the response parameters in the uncertainty propagation and probability of failure estimation. With the optimized design, uncertainty propagation in the responses due to input uncertainties is studied. The probabilities of failure due to uncertainty such as variability in geometric dimensions, material properties and load, and error in modeling and simulation are predicted for the different failure modes. Bootstrapping method is employed to evaluate the error in the probabilities of failure.

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