Modeling of Mechanical Ablation in Thermal Protection Systems

Abstract

An integrated thermomechanical modeling of response of low-temperature ablative thermal protection system under thermal loading encountered by reentry vehicles is presented. Of the three thermal protection mechanisms, thermal, chemical, and mechanical ablations, only the latter is assumed to influence the recession in the presence of aerodynamic surface shear for materials with low shear strength at higher temperatures. A model for the mechanical ablation (erosion) is presented that is based on the matching point scheme. The degenerated doubly curved shell element is employed in the modeling. This enables consideration of the general type of aerodynamic loads, distributed and varying with surface and time coordinates, which differs from the earlier studies reported in the open literature. The finite element method uses polynomial approximation to represent the nonlinear through-thickness temperature profile and explicit-through-thickness integration in the computation of element matrices. This brings in computational efficiency without loss of numerical accuracy, particularly in the context of multilayered construction. No attempt is made to compute the incident heat flux and other aerodynamic loads. Numerical examples are presented for specified loads to bring out the influences of material properties and heating rates on surface recession and are based mostly on assumed material properties.