化学气相沉积碳／碳复合材料性能研究

分析了化学气相沉积碳／碳（Ｃ／Ｃ）复合材料的刹车力矩和刹车速度的关系曲线及影响因素，结果表明，刹车力矩一刹车速度曲线上的初始力矩峰值随着摩擦界面温度的升高而增大，提高材料的石墨化度、改变刹车盘的结构、降低刹车比压的施加速度都可以降低初始力矩峰值，改善Ｃ／Ｃ材料的摩擦性能．Ｃ／Ｃ复合材料具有良好的自润滑性能，其磨损率仅为１．２×１０－３ｍｍ／次．它们具有较高的机械性能和热物理性能，完全可以满足飞机刹车的要求．     

两种双基体C/C复合材料的微观结构与力学性能

借助偏光显微镜、扫描电镜以及力学性能测试研究了两种双基体C/C复合材料的微观结构与力学性能。结果表明:基体碳在偏光显微镜下呈现出热解碳的光滑层组织,沥青碳的各向同性、镶嵌和流域组织。在SEM下普通沥青碳为"葡萄状"结构,中间相沥青碳为片层条带状结构。具有多层次界面结构的材料可以提高材料的弯曲强度,改善材料的断裂韧度,两种材料在载荷-位移曲线中载荷为台阶式下降,呈现出假塑性断裂特征。材料A和材料B的弯曲强度分别为206.68,243.66MPa,断裂韧度分别为8.06,9.66MPa·m1/2,材料B的弯曲强度、断裂韧度均优于材料A。     

影响炭／炭复合材料摩擦学性能的因素分析：材料的性质

影响炭／炭复合材料摩擦性能的因素很多，综述了国内外的研究现状，评价了材料的譬质对炭／炭复合材料摩擦磨损性能的影响，阐述了模量、石墨化度、密度、预制体的类型、基体类型、热解炭结构等因素。     

单向炭布叠层C/C复合材料的热压法制备及其性能

以经表面处理的石墨、单向炭布、和沥青粉为原料,通过热压烧结制备炭布叠层C/C复合材料.考察了炭布含量对材料密度、孔隙率、弯曲强度以及摩擦磨损的影响,采用MM200摩擦磨损试验机进行了环-块摩擦磨损实验,并借助SEM表征了材料的弯曲断口和磨痕形貌.结果表明:当炭布质量分数为50％时,C/C复合材料的综合性能最好,抗弯强度为112.2MPa,密度为1.72 g/cm3,摩擦系数为0.28,磨损率为3.68×10-13 m3·N-1·m-1.弯曲实验中材料呈“假塑性”方式破坏,断口出现大量纤维的拔出.石墨相含量的增加有利于形成较好的摩擦膜,降低磨损率,保持摩擦系数稳定.     

Properties of new polyimide foams and polyimide foam filled honeycomb composites

New polyimide foams and polyimide foam filled honeycombs are currently being developed at NASA, its licensee Sordal Inc. (USA) and Newmet (UK) under the trade name Solrex®. These materials are foreseen for Space, Aerospace, Maritime & Medicine applications. In this paper selected properties of these new materials with different densities are described. The investigated key properties are compression strength, thermal conductivity and moisture gain. The dependence of these properties on density, temperature and thermal cycling is discussed. Limits of the used characterisation methods are discussed. Possible applications are defined.     

短碳纤维的分散性对CFRC力学性能的影响

碳纤维增强水泥基复合材料(CFRC)是一种新型建筑智能材料,碳纤维在水泥基体中的分散性直接影响着它的力学性能.借助超声波和甲基纤维素(MC)分散剂,实现了短碳纤维在水泥基体中的均匀分散,对所制备的CFRC复合材料的断口形貌作了SEM观察;测试了试件的抗压强度、抗拉强度和抗折强度.结果发现,碳纤维均匀分散时,复合材料的抗压强度提高19%,抗拉强度比不加碳纤维时提高2.2倍,弹性模量提高1.4倍.此外,复合材料的抗弯强度、抗折强度均高于未均匀分散时的强度.     

C/SiC复合材料的氧化对其内耗行为的影响

通过分析C/SiC在高温(1250、1300和1350℃)空气氧化过程中质量、强度、物相、气孔率、微观形貌演变规律, 并同时采用动态热机械分析仪测得内耗的变化趋势, 研究了氧化对其内耗行为的影响规律, 进而为以内耗表征复合材料的氧化行为奠定基础。为明确C/SiC各组元在氧化与内耗行为对应关系中所发挥的作用, 进一步研究了SiC陶瓷在1300℃、空气中的氧化与内耗行为之间的对应关系。结果表明: SiC陶瓷氧化对其内耗行为的影响规律不明显且影响程度较弱; C/SiC在氧化过程中的内耗行为受C相的氧化损伤控制, 且作用规律明显, 其内耗保持率曲线均出现峰值, 其中1250、1300和1350 ℃的峰值分别为6.65、3.48和1.59。     

不同C/C复合材料飞机刹车盘基本性能的对比分析

通过对比分析Dunlop、 B.F.Goodrich、Missier、Bendix和中南大学粉末冶金研究所制备的几种炭/炭复合材料的显微组织、石墨化度、导热系数、洛氏硬度、抗压、抗弯、层间剪切强度、摩擦磨损性能后,得出如下结论:C/C复合材料作为一种性能优良的制动材料,必须具有合理的炭纤维骨架结构,一定比例的粗糙层气相沉积炭结构,较高的石墨化度和垂直摩擦面方向上的导热系数;我国具有自己知识产权的C/C复合材料飞机刹车盘的研制工作已取得了较大的进展和突破,其各项性能指标与国外同类产品性能相当。     

Validation of microparameters in discrete element modeling of sea ice failure process

A GPU-based discrete element method (DEM) with bonded particles is investigated to simulate the mechanical properties of sea ice in uniaxial compressive and three-point bending tests. Both the uniaxial compressive strength and flexural strength of sea ice are related to the microparameters in DEM simulation including particle size, sample size, bonding strength, and interparticle friction coefficient. These parameters are analyzed to build the relationship between the material macrostrengths of sea ice and the microparameters of the numerical model in DEM simulations. Based on this relationship, the reasonable microparameters can be calculated by given macrostrengths in the applications of simulating the failure processes of sea ice. In this simulation, both uniaxial compressive strength and flexural strength of ice increase with the increasing ratio of sample size and particle size. The interparticle friction coefficient is directly related to the compressive strength but has little effect on the flexural strength. In addition, numerical simulations are compared with experimental data to show the performance of the proposed model, and a satisfactory agreement is achieved. Therefore, this microparameter validation approach based on macrostrengths can be applied to simulate the complicated failure process of sea ice interacting with offshore platform structures.     

Experimental investigation of effects of build parameters on flexural properties in fused deposition modelling parts

Additive manufacturing is a group of fabrication techniques that is used to build components by depositing material in a layer-by-layer manner. Fused deposition modelling (FDM) is one of the additive manufacturing techniques which is widely used for prototyping and production applications of thermoplastic components. In load-bearing applications, flexural and compression forces often coexist. In order to avoid failure under these loads, it is essential to study the mechanical properties of FDM components. The main focus of this research is to study the flexural properties of FDM components and to comprehend their dependence on various build parameters. It has been observed from a series of flexural tests that FDM parts have anisotropic properties and this anisotropy was not due to the material in use, but due to the fabrication process itself. In this study Ultem 9085 is used as the material to fabricate coupons with variations in build parameters including build direction, raster angle and negative air gap. A full-factorial experimental design was used to study the individual and combined effects of these build parameters on the flexural properties of the coupons. Solid and sparse-build styles were used in the coupon fabrication. Flexural properties investigated include flexural yield strength, flexural modulus, flexural strength/mass ratio and flexural modulus/mass ratio. Qualitative observation and reasoning is used to comprehend how the flexural properties are affected by the build parameters.     

Mechanical properties of carbon fiber paper reinforced thermoplastics using mixed discontinuous recycled carbon fibers

Market demand for carbon fiber (CF) increases annually. Therefore, owing to the growing amount of carbon fiber-reinforced plastic (CFRP) waste, CFRP manufacturers are attempting to develop and design materials and products by paying greater attention to ecological and economic factors. In this report, recycled CF (rCF) varieties with differing mechanical properties are mixed to determine the possibility of rCF application in future structural materials. 1, 3, 5, 8 and 10 MPa are investigated for proper compression molding pressure. The range of 5–8 MPa is recommended. Mixing different rCFs can control the mechanical properties of the material, which is valuable for current rCF applications. A modified rule of mixture (ROM) is used to discuss flexural modulus and flexural strength. The coefficients for ROM are given for different rCF.     

A study of the strength of carbon–carbon brake disks for automotive applications

Carbon–carbon composites are often used in high-temperature applications due to their high specific modulus, high specific strength, excellent heat resistance, high thermal shock resistance and chemical inertness. In this paper, the strength of carbon/carbon brake disks for automotive applications were tested and evaluated. The laminate material properties of carbon/carbon composites were evaluated via tension, compression and shear tests. The strengths of mechanically fastened composite joints for brake disks were tested and their failure criterion was established based on the maximum stress theory. Additionally, torsion tests of carbon/carbon brake disks were performed and the results were compared with those from a finite element analysis.     

Development and properties of advanced composites based on cork and nanometric silicon carbide-filled phenolic resin

This paper presents the obtaining of advanced materials based on cork powder as reinforcement and phenolic resin (PR) with silicon carbide (nSiC) nanofiller as matrix with potential applications in aerospace industry. Three formulations were obtained: one control sample PR/cork with no nanofiller, two nanofilled samples with 1 and 2 wt% nSiC loadings into the resin. The materials were tested by flexural and compressive mechanical tests to determine their strength and stiffness, to determine their friction coefficient by tribological tests, to determine their thermal decomposition behaviour by TG-DSC analysis and to evaluate their thermal behaviour by thermal shock tests when subjected to extreme temperature directly from room temperature. The material structure was analysed by SEM visualizing the fracture cross-section after mechanical testing. The test results illustrate that silicon carbide nanoparticles improve flexural and compressive strength, but also stiffness and friction coefficient, delay thermal decomposition onset and improve thermal shock resistance. All these sustain the PR/nSiC/cork materials as potential advanced materials candidates for thermal protection applications.     

C/C刹车盘快速致密化工艺及其性能

为了缩短C/C刹车盘制备周期并提高其性能,介绍了一种制备C/C飞机刹车盘的快速致密化工艺,即采用天然气与丙烷气的混合气体为炭源气体的等温压差CVI法。与常规致密化工艺（丙烯气为炭源气体的等温压差CVI法）相比,C/C刹车盘的CVI(Chemical vapor infiltration) 时间缩短了一半,其导热性能提高5%以上,拉伸、压缩、弯曲与剪切性能提高10%以上,摩擦磨损性能提高20%以上。      

碳纤维含量对碳纤维／中铜石墨复合材料减摩耐磨性能的影响

在干磨擦条件下，对不同碳纤维含量的碳纤维／中铜石墨复合材料，进行了５０ｈ的摩擦磨损试验并借助扫描电镜观察了综们的磨面，结果表明，随碳纤维 增加，碳纤维．中铜石墨复合材料的摩擦系数和磨损量均明显减少。     

Influence of nanotube content on the mechanical and thermo-mechanical behaviour of –COOH functionalized MWNTs/epoxy composites

Functionalized multi-wall carbon nanotubes (MWNTs) with carboxylic acid group (–COOH) have been utilized for the preparation of epoxy nanocomposites. Composites were synthesized using three different wt% (0.5, 0.75 and 1) of MWNTs via the solution mixing technique followed by ultrasonication. Mechanical and thermo-mechanical properties of the fabricated composites have been experimented for the suitability of this material in a variety of structural applications. The flexural modulus, strength, hardness, impact strength and storage modulus increased upon increasing MWNTs contents. Best results have been observed in nanocomposites with 0.75 wt% nanotubes loading, which showed 101, 166 and 61% enhancement in the flexural modulus, hardness and storage modulus, respectively, compared to neat epoxy. Achievement of uniform dispersion and hence formation of improved interface between nanotubes and epoxy was the reason behind the maximum enhancement at this wt%, which is further evidenced by the fracture surface morphology obtained from microscopical investigations.     

高性能针刺碳/碳复合材料的制备与性能

为获得高性能针刺碳/碳复合材料, 拓展其应用领域, 通过优化针刺工艺参数, 设计并研制了不同结构参数的针刺预制体。采用沥青高压致密化工艺将针刺预制体制备成一系列针刺碳/碳复合材料, 研究了针刺碳/碳复合材料的微观结构、力学性能和热物理性能。结果表明, 针刺预制体的针刺深度、针刺密度以及短/长纤维配比等对碳/碳复合材料的力学性能和热物理性能影响显著。当针刺深度为12 mm、针刺密度为22针/cm ²、短/长纤维比例为1.0 : 4.8时, 针刺碳/碳复合材料表现出优良的综合性能, 拉伸、压缩、弯曲、面内剪切和层间剪切强度分别达到207、228、285、54和28 MPa。     

孔隙率对碳纤维增强纸基摩擦材料摩擦磨损性能的影响

碳纤维增强纸基摩擦材料是应用于汽车自动变速器中的一种新型湿式摩擦材料. 在固定原材料配比和含量的基础上, 通过改变摩擦材料厚度, 制备出几种孔隙率不同的碳纤维增强纸基摩擦材料. 采用液体渗透法测试摩擦材料的孔隙率. 利用扫描电镜观察试样形貌. 通过惯量试验机研究孔隙率对碳纤维增强纸基摩擦材料湿态摩擦磨损性能的影响. 试验结果表明: 短切碳纤维在树脂基体中均匀分散, 相互桥接, 形成了大小不一的贯穿性孔隙; 随着孔隙率的增大, 摩擦力矩曲线趋于平稳; 动摩擦系数升高, 静摩擦系数降低, 磨损率增大.     

Low velocity impact of combination Kevlar/carbon fiber sandwich composites

Impact, compression after impact, and tensile stiffness properties of carbon fiber and Kevlar combination sandwich composites were investigated in this study. The different samples consisted of impact-side facesheets having different combinations of carbon fiber/Kevlar and carbon fiber/hybrid. The bottom facesheets remained entirely carbon fiber to maintain the high overall flexural stiffness of the sandwich composite. The focus of this research was to determine if any improvement in impact properties existed as a result of replacing the impact-side facesheet layers of carbon fiber with Kevlar or hybrid. Impact tests were conducted on different sample types to obtain information about absorbed energy and maximum impact force. Also, compression after impact tests were conducted to determine the reduction in compressive strength when comparing impacted to non-impacted samples. The elastic moduli of carbon fiber, Kevlar, and hybrid were determined from tensile testing. This data was used to characterize the reduction in stiffness from replacing carbon fiber layers with the Kevlar or hybrid layers. The experimental data in its entirety helps define the benefits and disadvantages of replacing carbon fiber layers with Kevlar or hybrid.     

两种不同界面结合强度碳/铝复合材料的内耗特性

本文研究了两种不同界面结合强度的碳/铝复合材料经不同次数加载热循环处理后的内耗值及内耗机制。弱界面结合的C/L2复合材料的内耗值变化主要由界面脱粘引起,而强界面结合的C/LD2复合材料的内耗值变化主要由位错运动所致。