13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Micromechanical modeling and numerical simulation of ablation of 3D C/C composites Na Liu , Qingsheng Yang* Department of Engineering Mechanics, Beijing University of Technology, Beijing, 100124, China * Corresponding author: Email: qsyang@bjut.edu.cn; Tel: 86-10-67396333 Abstract Carbon-carbon (C/C) composites, in which a carbon matrix is reinforced by carbon fibers, are mainly used as thermo-structural protections in the aerospace engineering. The ablation of C/C composites at high-temperature causes mass loss, which is dominated by coupling effect of physical, chemical and mechanical factors. This paper classified the C/C ablation into three types according to the ablation mechanism: linear-rate reaction, parabolic-rate reaction and logarithmic-rate reaction. In this work, a micromechanical model of C/C composite with high-temperature heat conduction was established. A linear heat-transfer finite element analysis was carried out for revealing the damage morphology of C/C composites at an ultra high temperature. Keywords C/C composites, ablation, surface recession, thermal damage 1. Introduction Thermal protection materials, which are highly required in advanced thermal protection systems and envisioned for use on future hypersonic and space craft, will inevitably be subjected to utmost high temperature and strong oxidizing environment, such as the intercontinental ballistic missile nose cap often suffer an ultra high temperature of 7000~8000K atmosphere, dozens of megawatt heat flow density, unexpected high erosion of particle cloud and nuclear radiation in reentry [1]. Ablation phenomenon is frequent occurrence on the re-entry progress of space shuttle or rocket caused by aerodynamic heating, which can heat the surface of spacecraft up to a extremely high temperature in seconds. The thermal energy may lead to solid surface melting, evaporation, sublimation or decomposition of solid surface in the ultra temperature environment. Therefore, it is important for protecting the inner structure and astronauts from high temperature thermal damage. Carbon-carbon(C/C) composites consist of carbon matrix and reinforced carbon fibers[2] and possess a series of excellent mechanical properties, such as high temperature resistance, low density, high specific modulus, high specific strength, small coefficient of thermal expansion, high ablation resistance and high temperature resistant. Therefore, C/C composites are widely used in technological applications as excellent ablation resistance and thermal protection materials, e.g. solid rocket motor (SRM) nozzle throats, reentry rocket nose cone, missile nose-tips and leading edges [3,4]. In the ablation process, the sublimation or decomposition of C/C composites will take away lots of heat and the surface temperature of aerospace craft will be effectually lowered down. Consequently, the ablation resistance of C/C composites is directly related to the strengths of astrovehicle, determining the achievement of task scheduled. Hence, the research on the ablation of C/C composites has a great significance. In generally, researchers investigate the ablation mechanism of C/C composites in high temperature environment from two aspects: experiment research and numerical simulation research. The experiment is an effective method to understand the ablation mechanism of C/C composites. Unfortunately, the experimental simulation is extremely expensive because of the complexity of the extreme environmental conditions. Therefore, computer-based numerical simulation, which can predict the thermo-mechanical response of these composite heat shields, have become an effective method for analyzing the ablation behavior of C/C composites. Ultimately, it will achieve the design
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