碳/酚醛复合材料烧蚀行为预报方法

为研究用于钝头体高超声速飞行器热防护系统的碳/酚醛复合材料在典型服役环境下的烧蚀机制,首先,建立了烧蚀行为的数学模型,模型考虑了材料表面热辐射、固体相的温升吸热、基体热解反应吸热、高温热解气体引射、质量引射引起"热阻塞"效应、热解气体的温升和膨胀吸热等多种能量耗散机制,并利用有限元方法实现了数学模型的求解;然后,预报了在冷壁热流为400 kW·m-2、焓值为5 MJ·kg-1的气动热环境下碳/酚醛复合材料的烧蚀行为。结果表明:在受热过程中,厚度为20 mm的碳/酚醛复合材料碳化层的深度持续增加, 100 s时的表面温度达到1420 K,背壁温度为346 K,热解气体压力达10.3 atm,碳化层深度为7.50 mm。所得结论可为具有长时间大面积热防护需求的高超声速飞行器的热防护系统设计提供支持。      

Compaction of thick carbon/phenolic fabric composites with autoclave method

Carbon/phenolic composites are used in the nozzle parts of solid rocket motors due to their heat-resisting, ablative, and high strength characteristics, which are required to endure the high temperature and pressure of combustion gas passing through the nozzle. But the thick axi-symmetric structure of the composite nozzle induces high thermal residual stresses due to the large difference of coefficient of thermal expansion (CTE) between the in-plane and the out-of-plane. In this work, in order to reduce the through-thickness CTE and the void content, a compression in the thickness direction was applied to the composite prepreg by a compressive jig during manufacturing of composite to supplement the low autoclave pressure. The through-thickness CTE of the fabric composite was calculated by a compaction model and compared with the measured one by thermo-mechanical analysis. The through-thickness CTE changed drastically with respect to the compaction amount, and the void content of the carbon/phenolic fabric composite laminate showed different characteristics from the ordinary fabric laminates with respect to the autoclave pressure and the jig pressure.     

炭纤维增强氮化物复合材料的制备及其烧蚀性能

合成了硼吖嗪和全氢聚硅氮烷的混杂先驱体并对其结构进行了表征;以混杂先驱体和3D炭纤维编制体为原料,采用先驱体浸渍-裂解(PIP)工艺制得了炭纤维增强氮化物基体的复合材料,并对复合材料基体的抗氧化性以及抗烧蚀性能进行了研究。结果表明:混杂先驱体中含有B-N、B-H、Si-N、Si-H、N-H等结构,无其他杂质;基体材料在空气中具有优良的抗氧化性能,温度升至1000℃时仍未发生明显的质量变化,明显优于C/C复合材料;四个PIP工艺循环所制得的复合材料烧蚀表面平整,氮化物基体比增强炭纤维具有更好的耐烧蚀性能。     

含炔基酚醛树脂改性PSA及碳纤维布/PSA-EPAN复合材料性能

合成了乙炔基苯基偶氮酚醛树脂（EPAN）,通过溶液共混的方法用其对含硅芳炔树脂（PSA）进行改性,研究了PSA-EPAN树脂的热性能,并制备了PSA-EPAN的碳布预浸料,经热模压制备碳纤维布（T300CF）增强PSA-EPAN复合材料,对其力学性能进行了研究。结果表明：EPAN均匀分布于PSA树脂中,EPAN共混改性PSA树脂的固化温度提高,混入质量分数为7%的EPAN,N₂中固化PSA-EPAN树脂在800℃残留率超过90%,其玻璃化转变温度高于500℃,PSA-EPAN共混树脂浇铸体的弯曲性能高于PSA树脂,达40.7 MPa,提高了95.5%;PSA树脂经T300CF/PSA-EPAN复合材料力学性能显著提高,弯曲强度达到了423.5 MPa,提高了74%,层间剪切强度（ILSS）提高至29.53 MPa,增加了65%。     

The friction and wear properties of carbon nanotubes/graphite/carbon fabric reinforced phenolic polymer composites

In this paper, either graphite (Gr) or carbon nanotubes (CNTs), or both of them were incorporated into carbon fabric reinforced phenolic (CFRP) composites, preparing by a dip-coating and heat molding process, the tribological properties of the resulting composites were investigated using a block-on-ring arrangement. The worn surfaces were observed by scanning electron microscope to understand the mechanism. Experimental results showed that the optimal Gr was more beneficial than CNTs in improving the tribological properties of the CFRP composites when they were singly incorporated. It is well worth noting that the friction and wear behavior of the CNTs-filled CFRP composites were improved further when Gr was added, indicating that there is a synergistic effect between them. Tribological tests under different sliding conditions revealed that the Gr and CNTs-filled CFRP composites seemed to be the most suitable for tribological applications under higher sliding speed and load, and oil lubrication.     

Effects of carbon nanotubes and carbon fiber reinforcements on thermal conductivity and ablation properties of carbon/phenolic composites

The ablation properties and thermal conductivity of carbon nanotube (CNT) and carbon fiber (CF)/phenolic composites were evaluated for different filler types and structures. It was found that the mechanical and thermal properties of phenolic-polymer matrix composites were improved significantly by the addition of carbon materials as reinforcement. The concentrations of CF and CNT reinforcing materials used in this study were 30 vol% and 0.5 wt%, respectively. The thermal conductivity and thermal diffusion of the different composites were observed during ablation testing, using an oxygen–kerosene (1:1) flame torch. The thermal conductivity of CF mat/phenolic composites was higher than that of random CF/phenolic composites. Both CF mat and CNT/phenolic composites exhibited much better thermal conductivity and ablation properties than did neat phenolic resin. The more conductive carbon materials significantly enhanced the heat conduction and dissipation from the flame location, thereby minimizing local thermal damage.     

Fabrication of superhydrophobic 3-D braided carbon fiber fabric boat

A novel superhydrophobic carbon fiber fabric boat was prepared by combination of macro-scale rough surface and low surface energy material treatment. The loading capacities of the boats, fabricated from the resulting superhydrophobic fabrics, were also performed. The highest loading weight, 14.80 g, was obtained by a fabric boat treated with 12.0 wt.% HFTES. The striking loading capacity of the superhydrophobic boat is attributed to the air film trapped around the fabric surface.     

三维间隔连体织物复合材料力学性能

三维间隔连体织物复合材料是由纤维连续织造呈空芯结构的三维间隔连体编织物作增强体的新型轻质夹层结构 , 具有整体性、 轻质、 可设计、 低成本等特点。本文中对三维间隔连体织物复合材料增强体的结构特征进行了分析 , 考察了材料在平压、 剪切和三点弯曲载荷作用下的力学特性及破坏模式 , 并分析了织物结构参数对复合材料平压、 剪切、 三点弯曲性能的影响。结果表明 : 随芯柱高度的增加 , 材料的压缩强度和剪切强度降低 ,弯曲刚度增加; 随芯柱密度的增加 , 材料的压缩强度、 剪切强度和弯曲刚度都有大幅度的提高 , 且纬向剪切强度和弯曲刚度都大于经向。研究结果为该类材料的结构优化设计和性能分析奠定了重要基础。     

碳/酚醛防热复合材料烧蚀行为的数值模拟

碳/酚醛复合材料被广泛地应用于钝头体表面,是飞行器优秀的热防护材料。为了准确地预测其烧蚀性能,本文从复合材料的组成物纤维和基体的角度出发,基于能量、质量守恒和热分解方程,考虑了烧蚀过程中材料热属性的非线性变化和烧蚀面的退缩,分别计算了纤维和基体的烧蚀性能,预测了烧蚀过程中防热复合材料的温度分布、密度变化、质量损失规律及热属性和线烧蚀率等。结果表明：碳/酚醛复合材料的烧蚀是各种因素相互作用、相互影响的高度非线性过程;烧蚀过程中材料结构具有不均匀的温度分布,烧蚀面区域材料密度衰减最大并且材料的质量损失和损失率几乎呈线性增加;纤维和基体的烧蚀行为存在明显差异,分别预测两者的烧蚀性能,可以为热防护材料的设计提供更加准确的参考和依据。     

Compressive fracture behavior of 3D needle-punched carbon/carbon composites

Compressive fracture behavior under transverse and longitudinal compressive loading are determined for 3D needle-punched carbon/carbon (C/C) composites with single rough laminar (RL) pyrocarbon matrix or dual matrix of RL pyrocarbon and resin carbon. The results of Weibull statistics analysis indicate that scale parameter σ₀ of transverse and longitudinal compression of the composites with single matrix are 153.41 and 94.26 MPa, and σ₀ of the composites with dual matrix are 205.16 and 105.33 MPa, respectively. The mean compressive strength of both composites is nearly equal to σ₀ under each experimental condition. Failure modes of both composites under transverse and longitudinal compressive loading are shear and extension, respectively. Both composites exhibit quasi-ductile fracture behavior under transverse compression. Many small fragments of fibers and matrix carbon on the fracture surface of the composites are observed for single matrix composites. And the fiber bundle breakage with extensive debonding occurs for dual matrix composites. Under longitudinal loading, the composites with single matrix show quasi-ductile fracture behavior and delamination and splitting of non-woven long carbon fiber cloth layers are observed. The composites with dual matrix exhibit catastrophic failure behavior and crack runs through the composites along compressive loading direction.     

功能化Al2O3@SiO2/酚醛环氧-双马树脂复合材料的微观结构及性能

采用溶胶-凝胶法(Sol-gel)分别制备Al₂O₃和SiO₂,同时以KH560为架桥剂制得SiO₂包覆Al₂O₃(KH560-Al₂O₃@SiO₂)的增强体。以双马来酰亚胺树脂和酚醛环氧树脂(MBMI-EPN)为基体、4’4-二氨基二苯甲烷(DDM)为固化剂,采用原位聚合法制备了KH560-Al₂O₃@SiO₂/MBMI-EPN复合材料;表征KH560-Al₂O₃@SiO₂的微观结构及该增强体对复合材料性能的影响。结果表明:Al₂O₃@SiO₂粒子微观结构清晰,核壳结构完整,内核为短纤维状Al₂O₃,外壳为无定形SiO₂,二者通过化学键方式相连;Al₂O₃@SiO₂表面成功接枝上KH560基团,粒子堆积现象减弱。KH560-Al₂O₃@SiO₂/MBMI-EPN复合材料的微观形貌显示:KH560-Al₂O₃@SiO₂在MBMI-EPN基体中形成多相结构、分散性较好、界面作用稳定且断面形貌呈鱼鳞状,并未发现Al₂O₃@SiO₂粒子团聚体,整体结构完整。当KH560-Al₂O₃@SiO₂含量为1.5wt%时,复合材料的弯曲强度与冲击强度分别为126 MPa和14.7 kJ/m;,比树脂基体分别提高了21.2%和27.8%;材料的热分解温度为392.3℃,比树脂基体提高了14.5℃,力学性能和耐热性得到明显改善。     

Impact and post impact behavior of layer fabric composites

In this study, the effect of impact and post impact behavior of E-glass/epoxy composite plates having different layer fabrics were investigated by considering energy profile diagram and the related load–deflection curves. Different impact energies (5 J–60 J)were subjected to the plates consisting of eight layers of plain weave (1D), double (2D) and triple (3D) layer fabrics. The impact tests were continued until complete perforation of layer fabrics. The damage modes and damage processes of layer fabrics under varied impact energies were also discussed. At the end of the impact tests, the damaged samples were mounted into a compression apparatus to determine the Compression After Impact (CAI) strength of layer fabric samples. The results of these impact and post impact tests showed that contact force occurring between the impactor and the composite specimen increased and the CAI strength reduced by increasing the impact energy. The objective of this study was to determine the perforation threshold of E-glass/epoxy composite plates having different layer fabrics as plain weave (1D), double (2D), and triple (3D) layer fabrics.     

Evaluation of the interfacial bond properties between carbon phenolic and glass phenolic composites

The effects of moisture and surface finish on the mechanical and physical properties of the interfacial bond between the carbon/phenolic (C/P) and glass/phenolic (G/P) composite materials are presented in this paper. Four flat panel laminates were fabricated using the C/P and G/P materials. Of the four laminates, one panel was fabricated in which the C/P and G/P materials were cured simultaneously. It was identified as the cocure. The remaining laminates were processed with an initial simultaneous cure of the three C/P billets. Two surface finishes, one on each half, were applied to the top surface. Prior to the application and cure of the G/P material to the machined surface of the three C/P panels, each was subjected to specific environmental conditioning. Types of conditioning included: (a) nominal fabrication environment, (b) a prescribed drying cycle, and (c) a total immersion in water at 71 C. Physical property tests were performed on specimens removed from the C/P materials of each laminate for determination of the specific gravity, residual volatiles and resin content. Comparison of results with Shuttle Solid Rocket Motor (SRM) nozzle material specifications verified that the materials used in fabricating the laminates met acceptance criteria and were respresentative of SRM nozzle materials. Mechanical property tests were performed at room temperature on specimens removed from the G/P, the C/P and at the interface between the two materials for each laminate. The double-notched shear strength test was used to determine the ultimate interlaminar shear strength. Results indicate no appreciable difference in the C/P material of the four laminates with the exception of the cocure laminate, where a 20% reduction in the strength was observed. The most significant effect occurred in the bondline specimens. The failure mode was shifted from the C/P material to the interface and the ultimate strength was significantly reduced in the wet material. No appreciable variation was noted between the surface finishes in the wet laminate.     

Optimum design of weaving structure of 3-D woven fabric composites by using genetic algorithms

This paper discusses the optimum design method of the weaving structure of three-dimensional (3-D) reinforced composites. We propose the design method which combines the genetic algorithms (GA) and the finite element analysis. GA is one of the optimization techniques for the combinatorial optimization problem. In the finite element analysis, we used the original structure model which can express the fiber arrangement state in the 3-D composites faithfully. In this study, the original weaving structure model is constructed by combining the basic structure which has the fiber bundle and the cubic grid of resin. From analysis results, in the small design region, we can obtain the optimum weaving structure. Moreover, we proposed a new genetic operation, to design the weaving structure at the larger design region. These operations aim to prevent the failure of the partial weaving structure in the analytical model as much as possible. From the analysis results, the optimum weaving structure is obtained at the large design region, similar to above results. Consequently, it seems that the proposed method enables the design of the optimum weaving structure in the 3-D composites.     

三维间隔连体织物泡沫夹层结构复合材料的基本力学特性

将三维间隔连体织物泡沫夹层结构平压、剪切和三点弯曲载荷作用下的力学特性与三维间隔连体织物复合材料、传统泡沫夹层结构复合材料进行了对比分析,在此基础上,考察了芯柱高度、泡沫密度对复合材料平压、剪切、三点弯曲性能的影响。结果表明,三维间隔连体织物泡沫夹层结构复合材料承受平压载荷时,芯柱和泡沫存在协同效应;平压载荷作用下主要发生芯柱断裂破坏;随着芯柱高度增加,平压、剪切强度均减小;随着泡沫密度增加,平压强度近似呈指数增长。     

An analytical modelling technique for predicting the stiffness of 3-D orthotropic laminated fabric composites

A new analytical modelling approach for the prediction of the stiffness of 3-D orthotropic laminated composites is given. The composite, which consists of stacked orthotropic layers which are in turn composed of a number of parallel unidirectional stripes, is assumed to be homogeneous and orthotropic macroscopically. The technique introduced is to discretise the representative unit cell of the composite into slices (layers) and then stripes (elements). The stiffness of each slice can then be obtained under the condition of isostrain or isostress. The final stiffness of the composite is formulated analytically by combining these slices. The model eliminates the inconsistency between macro- and micro-level strains and gives more realistic distributions of strain for the representative unit cell. The results demonstrate that the present model, which is both simple and computationally efficient, can give a very accurate prediction compared with data from experiments and some existing models.