Thermal stress analysis of reentry vehicle nosetips at angle of attack

Abstract

The ASAAS (Asymmetric Stress Analysis of Axisymmetric Solids) computer program is applied to the prediction of thermal stresses in a reentry vehicle nosetip subjected to asymmetric temperature distributions and angle-of-attack loadings during reentry. This three-dimensional stress analysis computer program has the unique capability of properly accounting for the circumferential variation of temperature dependent material properties. It is based on a meridional finite element discretization of an axisymmetric solid combined with a Fourier series representation of circumferentially dependent variables. In contrast with similar methods where material properties cannot be expressed as a function of temperature, this method requires that the large system of equations be solved simultaneously. This is handled efficiently in ASAAS by several newly developed approaches to stiffness matrix generation and simultaneous equation solution. The nosetip analyzed is fabricated from an orthotropic, temperature dependent graphite material that is susceptible to thermal shock. Analyses are performed at several points in a trajectory and the effects of both aerodynamic heating and pressure loading are considered. The complete states of temperature, stress, strain and displacement throughout the graphite material are obtained as a product of ASAAS. Results are presented in the form of meridional contour plots at selected circumferential stations. The usefulness of ASAAS in performing angle-of-attack analysis of nosetips is evaluated by comparison to an axisymmetric analysis based on single ray heating. In addition, the convergence of solutions with increasing numbers of harmonics is demonstrated and computer run times are discussed.