防热材料高温烧蚀-相变特性的细观研究

通过高温环境下防热材料体积烧蚀机理的分析,利用细观力学的Eshelby等效夹杂方法研究了材料烧蚀-相变特性和热力学性能变化规律。假设材料热化学反应后热解生成相介质统计均匀分布,考虑了热解反应产生的气孔与固体相介质之间的相互作用,预报了不同基体材料弹性模量随温度、加温速率之间的变化关系,并与实验结果对照,吻合较好。     

多相纤维增强酚醛树脂低密度烧蚀防热复合材料高温压缩性能及损伤机制

低密度烧蚀防热材料是航天飞行器热防护系统的关键候选材料,其高温力学性能是热防护结构在气动热载荷下结构完整性的关键。本文针对多相纤维增强酚醛树脂低密度烧蚀防热复合材料开展高温压缩性能实验,获得了其压缩强度随温度的变化规律,结合热重、SEM分析了力载荷、热解及氧化反应对压缩强度的影响,揭示了软相碳层弥合和纤维脱黏、拔出两种韧化机制,为多相纤维增强酚醛树脂低密度烧蚀防热复合材料在热防护系统的工程应用提供实验数据支撑。      

树脂基材料的高温烧蚀变形

通过对树脂基材料高温热解反应过程中热化学烧蚀机理的分析,利用细观力学的Eshelby等效夹杂方法研究了材料高温烧蚀相变特性和热变形行为。假设材料体积烧蚀后,热解生成相介质统计均匀分布,考虑了热解反应产生的气孔与固体相介质之间的相互作用,预报了不同树脂基材料热膨胀系数与温度、加温速率之间的变化关系。与实验结果对照,吻合较好。     

防热复合材料高温炭化烧蚀过程的数值分析

为了揭示在高温情况下防热复合材料发生炭化烧蚀时的详细热响应,通过有限元数值模拟方法实现了对复合材料炭化烧蚀过程的计算。建立了防热复合材料炭化烧蚀过程数值分析的有限元模型,主要包括内部热解反应,材料质量损失,传热模型,表面炭层剥蚀模型,并对某炭/酚醛复合材料的烧蚀过程进行了数值模拟。结果表明,材料的烧蚀是多种因素综合作用的结果,随着烧蚀时间增加,材料内部会出现热解反应,并且发生炭化层、热解层和原始材料层的分层现象,各层随着时间向材料内部移动。壁面温度随着烧蚀量的增大而减小,材料的炭化烧蚀有效地起到了热防护效果。数值模拟结果满足研究项目要求。研究方法对任意的炭化烧蚀热防护材料均具有适应性。     

防热复合材料发展与展望

以烧蚀型防热复合材料、 非(微)烧蚀型防热复合材料、 高温高效隔热复合材料以及高温透波复合材料为重点, 简要总结了国内外防热复合材料发展现状, 介绍了我国重点领域的突破与进展, 并展望了未来防热复合材料的发展趋势。      

烧蚀防热复合材料用压力辅助RTM工艺

针对目前模压、缠绕等工艺成型烧蚀防热复合材料易造成层间结合差、脱粘、抗烧蚀性能差、易剥蚀等问题,提出了一种新型压力辅助RTM工艺,并对其进行了树脂充模流动模拟,制备了烧蚀防热复合材料,测试了材料的孔隙率、力学性能、烧蚀性能。结果表明:压力辅助RTM工艺具有可行性与优越性,复合材料孔隙率4.64%,层间剪切强度39.3 MPa,线烧蚀率0.017 mm/s,质量烧蚀率0.053 8 g/s。说明压力辅助RTM工艺适合成型烧蚀防热复合材料。      

航天飞行器热防护系统低密度烧蚀防热材料研究进展

当前,树脂基烧蚀防热仍被认为是最有效、最可靠、最成熟和最经济的一种热防护方式,在航天飞行器热防护系统中普遍采用。近些年在载人航天、探月工程、深空探测和新型航天飞行器系列工程的需求牵引下,本团队开发了蜂窝增强低密度材料、新型防隔热一体化材料、轻质烧蚀维形材料等先进防热复合材料,并开展了相应的应用基础以及工程应用研究工作,对烧蚀材料复杂防热机理及多重防热机制的协同作用进行了探索研究。随着再入/进入航天飞行器先进热防护系统需求的发展,功能多样化、兼容与集成是低密度树脂基烧蚀防热材料的主要发展趋势。     

碳纤维在高温下的结构、性能演变研究

针对碳纤维在碳/碳烧蚀防热复合材料中应用的基础问题,论述了不同碳纤维结构、成分、表面特征,及其力学性能和热物理性能的高温演变规律,揭示了碳纤维灰分含量对碳纤维力学性能和热氧化性能的影响。确定了在碳/碳复合材料复合成型过程中,碳纤维结构受基体碳影响的变化规律和碳纤维表面特征对碳/碳材料宏观力学性能的影响。阐明了碳/碳复合材料中碳纤维的力学性能对纤维发生折断烧蚀的阻碍作用和通过控制碳/碳成型最高温度实现提高性能的途径。     

低密度酚醛树脂基热防护复合材料的制备及性能

烧蚀热防护是目前最成熟且应用最广泛的一种卫星再入防热措施。本工作以酚醛树脂为基体,加入固体填料(空心玻璃微球、空心二氧化硅微球及空心酚醛微球)及纤维(石英纤维、碳纤维)制成一种低密度酚醛树脂基烧蚀热防护复合材料,并通过抗弯和压缩强度测试,隔热测试,烧蚀测试等方法对复合材料的性能与组分配比的关系及复合材料的烧蚀机理进行了分析。对比力学性能、隔热性能及抗烧蚀性能发现,复合材料密度的提高以及碳纤维含量的提高有助于提升复合材料的综合性能,最佳配比为密度0.6 g/cm³、5%石英纤维+5%碳纤维。对比烧蚀前后的成分发现,酚醛树脂在高温下炭化后会与SiO₂反应生成SiC,有助于提升复合材料的抗烧蚀性能。     

碳化锆陶瓷复合材料的制备、显微组织与性能

碳化锆(ZrC)陶瓷复合材料具有熔点高、密度低、耐烧蚀的优点, 在超硬、航天防热、新能源等领域应用前景广阔。本文概述了ZrC金属陶瓷和复相陶瓷、纤维增强ZrC复合材料的制备方法。着重介绍了粉末烧结、先驱体转化、反应浸渗等工艺的应用, 并讨论了不同制备工艺下复合材料显微组织的特点。在总结两类材料力学性能和烧蚀性能的基础上, 分析了各自的影响因素, 并指出ZrC金属陶瓷和复相陶瓷韧性低, 纤维增强ZrC复合材料烧蚀层易剥落的问题。最后总结展望了ZrC陶瓷复合材料相关研究的发展趋势。     

Constitutive relations for the thermomechanical behavior of fiber-reinforced inelastic laminates

The thermomechanical behavior of laminated composites in which every lamina is unidirectional fiber-reinforced thermoinelastic material is determined by a micromechanical analysis followed by a macromechanical one. In the micromechanical analysis, effective constitutive relations are derived for unidirectional fibrous materials in which the matrix and fiber phases are thermoelastic in the linear region and thermoinelastic in the nonlinear region. The derivation is based solely on the material properties of fibers and matrix and amount of reinforcement. By a macromechanics analysis the gross behavior of the laminated composite in stretching and bending deformation is determined. Applications are given for the deformation field developed in cooling and reheating of graphite/aluminium laminated plates.     

Modelling of the Mechanical Properties of Composite Materials at High Temperatures: Part 1. Matrix and Fibers

This paper is devoted to modelling the thermomechanical behaviour of charring composite materials at high temperatures. A multi-level model with an internal structure of unidirectional composite materials consisting of four structural levels is developed.With the help of this model, structural constitutive relations and expressions connecting elastic modules and strength characteristics of charring matrix and fibres with the properties of their internal phases are derived. Comparison of the model with experimental data for different types of matrices and fibres is conducted. Specific phenomena of the high-temperature behaviour of charring composites at high temperatures are analyzed.     

高温烧蚀条件下 C/C材料热力耦合场模拟

热防护材料在高温、高焓、高压环境中因物理、化学和力学因素造成质量损失引起材料烧蚀,使其热力学和热物理性质发生不可逆变化, 表现出复杂的非线性特征。通过对碳基复合材料热化学烧蚀机理分析, 由质量守恒、能量守恒及系统化学反应的热化学平衡原理, 建立相应的热化学和热力学烧蚀模型。基于材料线烧蚀引起边界移动建立热传导方程; 对温度场以及热应力场求解时充分考虑材料变物性特征。通过数值模拟表征材料在高温烧蚀条件下的动态热力学行为, 与实验结果吻合较好, 实现了材料在高温、高过载等复杂因素耦合作用下的实时仿真。      

SiO2-竹纤维协同改性对环氧树脂基复合材料摩擦磨损性能的影响

为了提高环氧树脂（EP）基复合材料的摩擦磨损性能,制备低成本耐磨材料,选用纳米SiO₂粒子和竹纤维（BF）等作为填料,制备了纳米SiO₂-BF/EP复合材料。通过摩擦磨损测试仪、动态热机械分析仪和SEM研究了纳米粒子和纤维对复合材料的耐磨性能、热学性能及微观结构的影响。研究结果表明:单独加入BF后,BF/EP复合材料的体积磨损较同条件下的纯EP大幅度降低,最多可降低71%;同时加入SiO₂纳米粒子和BF后,对纳米SiO₂-BF/EP复合材料的玻璃化转变温度和体积磨损影响显著,玻璃化转变温度比纯EP提高了11℃,达到了124℃,体积磨损较同条件下的纯EP下降了约75.3%。      

Multi-scale modeling of refractory woven fabric composites

Thermomechanical analysis of a refractory, woven fabric composite was conducted using a multi-scale analysis technique. The composite was made of carbons and ceramic materials. The fibers were made of carbons and the outer coating was made of a ceramic material. In order to reduce the thermal stress in the carbon fibers and the ceramic material caused by mismatch of coefficients of thermal expansion between the two materials, a graphitized carbon layer was introduced between the fiber and the ceramic coating. For the multi-scale analysis, a new analysis model was developed and used to bridge the micro-scale characteristics, i.e. the constituent material level such as carbon and ceramic materials, to the macro-scale behavior, i.e. the woven fabric composite level. Furthermore, finite element analyses were undertaken with discrete modeling of the representative fibers, coating, and the graphitized middle layers. Then, both multi-scale analytical and numerical results were compared. In this study, thermal stresses at the micro-level, i.e. in the fibers and coating materials, as well as effective thermomechanical properties of the refractory composites were computed using the multi-scale technique.     

On the matrix cracking stress and the redistribution of internal stresses in brittle-matrix composites

A concept is proposed to increase the matrix cracking stress of some brittle-matrix composites by taking advantage of the redistribution of internal stresses that occurs when a composite with phases that have dissimilar creep behavior is subjected to thermomechanical loading. The concept is elaborated through the stress analysis of a model unidirectional composite with constituents that exhibit linear viscoelastic behavior. It is shown that if a composite with a matrix that is less creep resistant than the fibers is subjected to a treatment involving both thermal and mechanical loading (e.g. creep test), stresses can be transferred from the matrix to the fibers, resulting in the stress–relaxation of the matrix. Furthermore, it is also shown that by the elastic recovery of the fibers, the matrix can be subjected to large compressive residual stresses at the end of the treatment. The conditions for the viability of this concept and the implications of fiber overloading and potential loss of composite-like behavior are discussed.     

The statistical second-order two-scale method for thermomechanical properties of statistically inhomogeneous materials

A statistical second-order two-scale (SSOTS) method is established in a constructive way for predicting the thermomechanical properties of statistically inhomogeneous materials. For this kind of composite materials, the complicated micro-characteristics of inclusions, including their shape, size, orientation, spatial distribution, volume fraction and/or material properties and so on, lead to changes of the macroscopic thermomechanical properties, such as stiffness, coefficient of thermal expansion and strength of material. In this paper, a statistical model at an arbitrary position of the composite material is defined to represent the microstructure of the statistically inhomogeneous media at first. And then, the statistical second-order two-scale analysis formulation is derived. Finally, the numerical results for some statistically inhomogeneous composites are calculated by SSOTS algorithm, and compared with the data by experimental and theoretical methods.