先进高温材料强度和抗热震性能研究

发布时间：2018-06-18 13:34

  本文选题：高温强度 + 抗热震性能　； 参考：《重庆大学》2016年博士论文

【摘要】：先进材料是指新近发展或正在发展之中的具有比传统材料性能更为优异的一类材料。目前,先进材料广泛应用于国防建设中,并服役于高温环境,其服役安全性是亟待解决的一个关键问题,研究这些材料的高温热学和力学性能对此十分重要。本文根据三类先进材料的研究现状,并结合各个科学问题的特点,采用理论、数值和试验方法研究了化学气相沉积硫化锌(CVD Zn S),超高温陶瓷材料(UHTCs)和单晶材料的高温强度和抗热震性能,主要开展工作如下:(1)通过在常规韧性材料拉伸夹具基础上做改进,提出了一套操作简单、加工方便、经济的脆性材料单轴直接拉伸强度测试装置。测试装置及测试方法的有效性通过测试的室温CVD Zn S单拉强度与三点弯强度的比值与文献中报道的其它脆性材料的比值相近,且测得的单拉强度和三点弯强度服从Weibull统计分布进行了验证。此外,为了设计和评估CVD Zn S头罩和侧窗,还测试了从室温到600°C的直接单拉强度和单轴压缩强度,并通过宏微观分析得到了CVD Zn S的拉伸和压缩失效机理和失效模式。(2)从临界失效能密度准则和临界应变准则出发建立了立方单晶和六方单晶的温度相关性理想拉伸强度模型,从而将单晶材料的温度相关性理想拉伸强度和温度相关性弹性性质,定压比热容(临界失效能密度准则)和线热膨胀系数(临界应变准则)联系了起来,进而将参考温度下的理想拉伸强度外推到其它温度。从理论上研究了立方单晶(W、Al和Fe)和六方单晶(Zr B2、Hf B2和Ti B2)的温度相关性理想拉伸强度,特别地,Al是从绝对零度到材料熔点的。计算结果和第一性原理(AI)、分子动力学(MD)和AI MD方法的结果进行了比较,通过理论分析说明了所建模型在预测单晶材料理想拉伸强度时的合理性,且说明了立方单晶和六方单晶的高温失效准则均为应变控制的。(3)成功地将半无限大体的瞬态温度解答应用到了UHTC薄板单一热环境下热冲击瞬态温度分布的计算中,并从热弹性理论出发推导了自由薄板的温度相关性热应力场模型,从而建立了单一热环境下UHTCs的温度相关性热冲击模型。对于复合热环境,根据有限体积法,推导得到了对流冷却情形下UHTC热防护系统的抗热震性能计算模型。所建模型的有效性均通过与有限元计算结果的对比进行了验证。详细研究了气动热环境和对流热环境下UHTCs的抗热震性能,定义了第一、二和三类热的边界条件下的传热条件,应用传热条件的概念得到了陶瓷材料不同热环境下的统一抗热震性能基本规律,并提出了临界传热条件来表征陶瓷材料的抗热震性能。传热条件和临界传热条件间的关系类似于应力和强度间的关系。临界传热条件强调的是材料永不发生热冲击失效,故临界传热条件不但可用于表征材料的抗热震性能,还可用于工程设计中作为安全设计参数。对UHTC热防护系统抗热震性能的研究表明,对流冷却可提高UHTC热防护系统的抗升温热震性能,但同时可能引入新的降温热冲击,为了确保对流冷却不会引起薄板的失效,对流冷却时的传热条件应小于相应的临界传热条件。(4)用理论和有限元数值模拟的方法详细研究了第一、二和三类热边条下工程中常见的9类约束方式和薄板面内几何形状对陶瓷构件抗热震性能的影响,给出了这9类约束方式的抗热震性能的排序和如何通过避免薄板面内几何形状和约束条件的非对称性来提高陶瓷构件的抗热震性能。
[Abstract]:Advanced materials are a kind of materials which have been developed or are developing more well than traditional materials. At present, advanced materials are widely used in the construction of national defense and are serving in high temperature environment. The safety of their service is a key problem to be solved urgently. The study of the thermal and mechanical properties of these materials is very important. Based on the research status of three kinds of advanced materials and the characteristics of various scientific problems, the high temperature strength and thermal shock resistance of chemical vapor deposition zinc sulfide (CVD Zn S), ultra high temperature ceramic materials (UHTCs) and single crystal materials are studied by means of theoretical, numerical and experimental methods. The main work is as follows: (1) through the conventional toughness On the basis of the tensile clamp, a set of simple, convenient and economical single axis tensile strength testing device for brittle materials is proposed. The ratio of the ratio of the single tensile strength to the three point bending strength at room temperature CVD Zn S is close to the ratio of the other brittle materials reported in the article. The measured single tensile strength and three point bending strength were verified by Weibull statistical distribution. In addition, in order to design and evaluate the CVD Zn S head cover and side window, the direct mono tensile strength and uniaxial compression strength from room temperature to 600 degree C were also tested. The tensile and compression failure mechanisms and failure modes of CVD Zn S were obtained by macro and micro analysis. (2) Based on the critical failure energy density criterion and the critical strain criterion, the ideal tensile strength model for the temperature dependence of the cubic and six square crystals was established. The temperature dependent elastic properties of the ideal tensile strength and temperature, the constant pressure ratio heat capacity (Critical inefficiency density criterion) and the linear thermal expansion coefficient (critical stress) were established. The ideal tensile strength of the reference temperature is extrapolated to other temperatures. The ideal tensile strength of the temperature dependence of cubic monocrystal (W, Al and Fe) and six square single crystals (Zr B2, Hf B2 and Ti B2) is theoretically studied. In particular, Al is from absolute zero to material melting point. Calculation results and first principle (AI) are divided. The results of the sub dynamics (MD) and the AI MD method are compared. The reasonableness of the model in predicting the ideal tensile strength of the single crystal material is explained by theoretical analysis, and the high temperature failure criteria of the cubic and six square crystals are all strain controlled. (3) the semi infinite transient temperature solution is successfully applied to the UHTC In the calculation of the transient temperature distribution of the thermal shock in a single thermal environment, the temperature dependent thermal stress field model of the free plate is derived from the thermoelastic theory, and the temperature dependent thermal shock model of UHTCs under a single thermal environment is established. For the complex thermal environment, the convective cooling is derived by the finite volume method. The thermal shock resistance calculation model of the lower UHTC thermal protection system. The validity of the model is verified by the comparison with the results of the finite element calculation. The thermal shock resistance of the UHTCs under the aerodynamic heat environment and the convective heat environment is studied in detail. The heat transfer conditions under the boundary conditions of first, second and three types of heat are defined and the heat transfer conditions are applied. The basic rule of the unified thermal shock resistance of ceramic materials under different thermal conditions is read, and the critical heat transfer conditions are proposed to characterize the thermal shock resistance of the ceramic materials. The relationship between the heat transfer conditions and the critical heat transfer conditions is similar to the relationship between the stress and the strength. The critical heat transfer conditions can be used not only to characterize the thermal shock resistance of the material, but also to be used as a safety design parameter in the engineering design. The study of the thermal shock resistance of the UHTC thermal protection system shows that the convective cooling can improve the thermal shock resistance of the UHTC thermal protection system, but at the same time it may introduce a new thermal shock reduction to ensure the convection cooling. The heat transfer conditions of the convective cooling should be less than the corresponding critical heat transfer conditions. (4) the influence of the 9 types of constraints and the geometric shape of the thin plate on the thermal shock resistance of the ceramic members under the first, second and three types of hot strip is studied by theory and finite element numerical simulation. The thermal shock resistance of the 9 types of constraints and how to improve the thermal shock resistance of the ceramic members can be achieved by avoiding the asymmetry of the geometric and constraint conditions in the thin plate.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O346
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本文编号：2035654