Temperatures and stresses in ablating hemispheres

Hypersonic wind-tunnel tests of thirteen 7 3/4-in.-diam Plexiglas and nylon hemispheres were designed and conducted at the Polytechnic Institute of Brooklyn utilizing a shrouded-model technique to simulate Mach 15 to 20 flight. The models were instrumented with thermocouples ans strain gages from which continous time histories of temperature and strain were recorded. In addition, ablation measurements were made after themodels were tested. The experimental results are compared with theoretical calculations of strain, temperature and ablation. Using a point-symmetric heat-balance method to determine the ablation and temperature histories, a thermal stress analysis is conducted in which variations in the modulus of elasticity with temperature are approximated by a concentric-layer technique. The effects of axisymmetric pressure distributions, as well as the effects of the boundary condition imposed by the model support, are considered in an axisymmetric alyer analysis. A comparison between theroy and experiment indicates good qualitative results and good-to-poor quantitative results. The details of the analyses, and the comparison between the theoretical predictions and experiment are discussed.