短切碳纤维骨架材料的力学及导热性能研究

发布时间：2018-06-24 23:03

本文选题：碳粘结碳纤维复合材料 + 纤维取向　；参考：《哈尔滨工业大学》2015年硕士论文

【摘要】：碳粘结碳纤维复合材料(carbon bonded carbon fiber composites CBCF),是一种低密度的短纤维碳/碳复合材料,具有高孔隙率、低密度、优异的耐高温特性以及较好的结构稳定性,被广泛用作气氛热解炉以及通用热源燃料仓的隔热材料。同时,利用该材料为增强相,通过浸渍酚醛树脂气凝胶得到新型超轻质烧蚀型热防护复合材料,可广泛应用于航空航天飞行器的热防护领域。本文采用低热导率的粘胶基碳纤维,通过水性浆料压滤成型、干燥、固化、碳化等工艺流程,制备了碳粘结碳纤维复合材料,这是一种是由裂解碳粘结相互独立的短切纤维构成的高孔隙率碳/碳复合材料。材料表面及内部纤维分布均匀,没有团聚,成束,分层等缺陷,碳纤维在高温处理后保持其原有的长直结构特点。在加压过程中短切碳纤维趋向垂直于压力方向的面内排布,纤维在垂直于压力的方向形成层状结构而在平行于压力方向的平面内随机分布。这种微观结构的各向异性决定了其力学和热物理性能的各向异性。短切碳纤维骨架材料的压缩性能具有各向异性特点。在压力平行于材料成型时加压排水方向的平行压缩过程,材料中表现出一定的“假”塑性特点,在与之垂直方向进行横向压缩过程中材料表现出与塑性材料类似的特征。材料的平行压缩强度S和弹性模量E随纤维长度的增加而降低,随材料密度增大而增加,并且密度越高受材料密度变化的影响越大;横向压缩时材料的屈服强度和能量密度基本不受纤维长度影响,随材料密度增加而增大。针对短切碳纤维骨架材料沿不同方向简化的二维模型、材料整体的三维模型计算其热导率,分析各项异性特点。改变纤维取向和密度,通过随机生长-生成方法建立了二维条件下的材料模型,并利用格子Boltzmann方法求解材料热导率。结果显示纤维取向角的限值为90°时,纤维在平面内呈随机分布,材料导热呈现各向同性特点,随着纤维取向角限值θ的减小,材料沿温度梯度方向热导率逐渐增大,垂直于温度梯度方热导率逐渐减小,其各项异性程度显著增加;材料热导率随着纤维体积分数的增加呈近似线性的增长趋势。利用Geo Dict软件根据纤维取向张量建立了不同三维层状模型并计算其热导率,材料导热性能仍呈各项异性,随层状程度增加其各项异性程度加剧。利用激光脉冲法测试材料室温条件下的热导率,结果与与计算结果一致,显示材料在不同方向表现出明显的各项异性特点。但两方向热导率的各向异性比为0.8左右,小于计算值(不高于0.54)。碳粘结点在x-y方向抑制热量传递而在z向促进热量传递导致材料热导率呈现的各向异性程度相较于计算结果偏小。
[Abstract]:Carbon bonded carbon fiber composite (carbon bonded carbon fiber composites CBCF) is a low density short fiber carbon / carbon composite with high porosity, low density, excellent high temperature resistance and good structural stability. It is widely used as heat insulation material for atmosphere pyrolysis furnace and general heat source fuel bunker. At the same time, by impregnating phenolic resin aerogel, a new type of ultra-light ablative thermal protection composite material was obtained by using the material as reinforcement phase, which can be widely used in the thermal protection field of aerospace vehicles. In this paper, carbon bonded carbon fiber composites were prepared by low thermal conductivity viscose based carbon fibers, which were prepared by water slurry pressure filtration molding, drying, curing, carbonization and other processes. This is a kind of high porosity carbon / carbon composite composed of short cut fibers which are independent of cracking carbon bond. The fibers on the surface and inside of the material are uniformly distributed, without agglomeration, bunching, delamination and other defects. The carbon fiber keeps its original long and straight structure after high temperature treatment. During compression, the short cut carbon fibers tend to be arranged in plane perpendicular to the pressure direction, and the fibers are randomly distributed in the cambium structure perpendicular to the pressure direction and in the plane parallel to the pressure direction. The anisotropy of the microstructure determines the anisotropy of its mechanical and thermophysical properties. The compression properties of short cut carbon fiber skeleton are anisotropic. In the process of parallel compression of pressure and drainage direction when the pressure is parallel to the material forming, the material shows certain "pseudo-plastic" plastic characteristics, and the material exhibits similar characteristics to the plastic material in the process of transverse compression in the vertical direction. The parallel compressive strength S and elastic modulus E decrease with the increase of fiber length and increase with the increase of material density, and the higher the density is, the greater the change of material density is. The yield strength and energy density of the material under transverse compression are not affected by the fiber length, but increase with the increase of the material density. According to the simplified two-dimensional model of short cut carbon fiber skeleton material in different directions, the three-dimensional model of the material is used to calculate its thermal conductivity and analyze the heterogeneity. By changing the orientation and density of the fibers, the material model under two dimensional conditions was established by random growth-generation method, and the thermal conductivity of the materials was calculated by the lattice Boltzmann method. The results show that when the limiting value of the fiber orientation angle is 90 掳, the fiber is randomly distributed in the plane, and the heat conduction of the material is isotropic. With the decrease of the limiting value 胃 of the orientation angle, the thermal conductivity of the material increases along the temperature gradient. The thermal conductivity perpendicular to the temperature gradient decreases gradually and the heterogeneity increases significantly, and the thermal conductivity increases linearly with the increase of fiber volume fraction. Geo strict software was used to establish different three-dimensional layered models based on fiber oriented Zhang Liang and calculate their thermal conductivity. The thermal conductivity of the material is still different, and the heterogeneity of the material increases with the increase of the laminar degree. The laser pulse method is used to measure the thermal conductivity of the materials at room temperature. The results are in agreement with the calculated results and show that the materials show obvious heterogeneity in different directions. However, the anisotropy ratio of the two directions is about 0.8, which is less than the calculated value (not more than 0.54). Carbon bond point inhibits heat transfer in x-y direction and promotes heat transfer in z direction. The anisotropy of thermal conductivity of the material is smaller than that of the calculated results.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB332

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