【作者】 杨德军；

【导师】 李旭东；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2013， 博士

【摘要】 防热复合材料具有优良的高温性能,在高温烧蚀环境下可以通过自身发生烧蚀带走大量热量,减小了热量向结构内部的传递,从而有效的保护了内部结构,起到了热防护的作用。因此在工程应用领域对防热复合材料烧蚀行为进行研究具有重要的应用价值。防热复合材料在高温、高焓、高压的烧蚀环境中会发生一系列物理化学反应,从而发生质量损失引起材料的烧蚀。可以通过对复合材料热化学烧蚀机理进行分析,耦合能量守恒原理、质量守恒原理和热化学反应平衡原理建立复合材料的热化学烧蚀模型。材料烧蚀过程中存在一个随烧蚀时间移动的边界,需要对烧蚀移动边界条件下防热复合材料的温度场进行求解。有限元数值模拟方法是解决复杂工程问题中最常用的方法,且目前针对不同的工程应用问题已经开发出了各类有限元计算软件。另外,有限元数值分析软件在对研究问题进行数值计算分析时,还提供了强大的后处理功能,可以方便的对计算模型进行分析和探讨。本文研究工作中,通过有限元数值计算软件对不同的防热复合材料建立了烧蚀模型,并对结构划分了有限元网格,对有限元数值计算结果进行了研究和分析。在高温环境下防热复合材料会发生热化学烧蚀,在热化学烧蚀作用下防热复合材料会发生一系列物理化学变化。运用化学平衡原理对碳基复合材料在高温条件下发生的热化学反应进行了数值计算,对其在不同表面温度下烧蚀产物分布进行了分析。采用有限元数值模拟方法对不同工况下碳／碳复合材料热化学烧蚀作用下的温度场进行了计算和分析。碳基复合材料在高温环境下会与空气组元发生化学反应,主要包括碳的氧化反应、碳的升华反应以及碳氮反应等。对碳／碳复合材料在烧蚀作用下的温度场进行了数值分析。通过热化学烧蚀原理和表面能量平衡计算了烧蚀表面的热流,耦合复合材料内部热传导方程对其温度场进行了计算和分析。对高温环境下烧蚀表面的退缩进行了数值仿真,计算了烧蚀移动边界条件下碳／碳复合材料的温度场分布。通过对热化学烧蚀机理的分析,利用有限元方法分析了热化学烧蚀、烧蚀表面退缩及温度场耦合作用下C/C复合材料的烧蚀性能变化规律。采用虚拟失效、重新构建网格部件的方法实现烧蚀表面的退缩,建立了烧蚀表面退缩下瞬态温度场的有限元模型。运用热化学烧蚀理论求解了进入材料内部的净热流和烧蚀率。烧蚀表面退缩后变得不规则,通过编程校正了重新加载热流时不规则表面出现局部热流偏大的现象。研究结果表明,随着烧蚀时间的增加,进入材料内部的热流达到动态的平衡,材料的烧蚀是多种因素综合作用的结果,通过耦合计算可以真实反映材料的烧蚀特性。为了揭示在表面烧蚀条件下防热复合材料内部发生碳化时的详细响应,通过有限元数值计算方法对某碳/酚醛复合材料的碳化烧蚀过程进行了数值分析。应用ALE(Arbitrary Lagrange-Euler)动网格方法实现了材料发生表面烧蚀时的边界退缩,并用Arrhenius定律对烧蚀过程中材料内部的热分解进行了建模。耦合计算了材料发生烧蚀时内部热解反应,温度场分布,碳层及物性参数的变化。研究结果表明,烧蚀过程中,材料的热解由烧蚀表面向材料内部渗透,且热解反应程度随着烧蚀时间逐渐减小。材料内部热解的持续渗透,使得材料内部发生质量损失,出现碳化层、热解层和原始材料层的分层现象。在多种因素的耦合作用下,材料的碳化烧蚀有效的起到了热防护作用。更多还原

【Abstract】 Thermal protective composites have excellent high temperature performance. The material takes away a lot of heat and reduce the heat transfer to the inside structure through ablation, which effectively protect the internal structure and have the effect of the thermal protection. So the research of thermal ablation behavior of composite materials has important application value in the field of engineering.Thermal protective composites will occur a series of physical and chemical reaction in high temperature, high enthalpy and high pressure environment, which produce quality loss due to material ablation. The composites were analyzed by thermal chemical ablation mechanism. The principles of conservation of energy, mass conservation principle, the principle of thermal chemical reaction equilibrium are coupled to thermal chemical ablation model. A moving boundary exists in the process of materials ablation time, so, we need to solve the temperature field of composite materials under ablation moving boundary conditions.Finite element numerical simulation method is the most commonly used method to solve complex engineering problems. All kinds of finite element calculation software have been developed according to different engineering applications. In addition, the finite element numerical analysis software also provide powerful post-processing function in the numerical analysis of the research question, which can be convenient for analyzing and discussing the calculation model. In research work of this paper, different thermal protective composites ablation model is established through the finite element numerical calculation software, and the finite element grid was divided to the structure, and finally the finite element numerical calculation results are studied and analyzed.Thermal protective composites will occur thermo chemical ablation and a series of physical and chemical changes. The thermal chemical reaction of carbon composite material is numerically calculated using the principle of chemical equilibrium under the condition of high temperature, also, the ablation products distribution under different surface temperature was analyzed. Temperature field of carbon/carbon composites under the action of thermal chemical ablation was calculated and analyzed by finite element numerical simulation methods. Carbon composite material will react with air components under high temperature environment, mainly including carbon oxidation reaction, the sublimation of carbon and carbon and nitrogen. Temperature field of carbon/carbon composites was numerically analyzed under the action of the ablation. The ablation surface heat flow was calculated through the principle of thermal chemical ablation and the surface energy balance, and its temperature field is calculated and analyzed coupling the internal heat conduction equations. The receding ablation surface under the environment of high temperature was numerically simulated. Temperature field distribution of carbon/carbon composites was calculated under moving ablation boundary conditions.In this paper, according to the analysis of the thermo-chemical mechanism, the change rules of ablation properties of C/C composites in thermo-chemical ablation, ablation surface receding and temperature field coupling was investigated by finite element method. Achieved the receding of the ablation boundary by virtual failure and rebuilding orphan mesh part, and established finite element model of ablation temperature field at receding boundary conditions. The net heat flux flowed into the material and ablation rate was calculated by thermo-chemical ablation theory. The phenomenon of large local heat flux on the irregular surface was corrected by programming after ablation surface receding when the heat flux was reloaded. Research shows that as the ablation time increases, the heat flux flows into composite materials will reach a dynamic balance. The ablation of the material is the results of a variety of factors and coupled calculation can truly reflect the characteristics of the ablation of the material.For revealing the detailed response of thermal protective composites in the process of internal carbonization, the carbonized ablation process of carbon/phenolic composite materials is analyzed by the method of finite element numerical simulation. The ablation surface receding is achieved by ALE moving mesh methods. The internal material pyrolysis in process of ablation is established by Arrhenius laws. The internal pyrolytic reactions, temperature distribution, the changes of carburization zone and material properties are coupling calculated when the ablation occurs. Research results show that the pyrolysis of the material is penetrated from ahlation surface to inner materials. The degree of pyrolysis reaction decreased with time. Internal quality loss happens through incessancy penetrating of the internal material pyrolysis, which cause the material been divided into carburization zone, pyrolytic zone and original material zone. Charring ablative material played an effective thermal protection function under coupling of a variety of factors.更多还原