Multiscale Modeling Of Surface Ablation On Carbon/Carbon Composites

Carbon/carbon composites, in which a carbon matrix is reinforced by carbonfibers, offer a unique set of properties like low density, high specific strength, goodresistance to thermal shock and ablation. The stagnation temperature of thosematerials can up to10000℃. Especially, they can keep high strength undernon-oxidizing condition above2000℃, which make carbon/carbon compositesbecome the best ablative resistant materials in reentry space. The carbon/carboncomposites are mainly used in the field of ablation resistance, friction resistance,thermal protection structure, radiation resistance, high-temperature thermal structureand others.As thermal protection materials, the service environment of the carbon/carboncomposites is unusually severe, and the oxidation and ablation can reduce the strengthof the carbon/carbon composites apparently. Thus, the research of ablation oncarbon/carbon composites has been a hot topic. Because of uncertainenvironmental parameter, different properties at different scales and expensiveexperimental cost, the experimental research of ablation mechanism on carbon/carboncomposites is limited.This thesis mainly studied the ablation of carbon/carbon composites during hightemperature by numerical simulation. The main research contents are as follows.(1) According to the experimental results, a law of the surface recession oncarbon/carbon composites by ablation was established. The relations betweentemperature, ablation time, activation energy and surface ablation of carbon/carboncomposites are described by Arrhenius reaction rate. It is assumed that the initialoxidation temperature is400℃, and the critical transition temperature is873℃. Thecritical temperature can affect the activation energy. By user subroutineUMESHMOTION of ABAQUS, the numerical simulation of ablation was carried out.(2) A macroscopic model of the ablation of carbon/carbon composites wasestablished. The ablation modeling was based on the subroutine to control surfaceablation. It focused on the ablation change, surface roughness morphology duringablation and the influence of ablation rate on ablation.(3) In micromechanical scale, the carbon/carbon composites were modeled toanalyze the ablation change, surface roughness, influence of temperature and thevariation of ablation for the composites with different volume fractions of fibers.(4) The influence of ablation on mechanical properties of carbon/carboncomposites with inner hole, including ablation morphology of the hole, degradationlaw of tensile strength, and degradation law of compressive strength before and after ablation were studied.