Preparation, Properties and Application of C/C-SiC Composites Fabricated by Warm Compacted-in situ Reaction

Carbon fibre reinforced carbon and SiC dual matrices composites (C/C-SiC) show superior tribological properties, high thermal shock resistance and good abrasive resistance, and they are promising candidates for advanced brake and clutch systems. The microstructure, mechanical properties, friction and wear properties, and application of the C/C-SiC composites fabricated by warm compacted-in situ reaction were introduced. The results indicated that the composites were composed of 50-60 wt pct carbon, 2-10 wt pct residual silicon and 30-40 wt pct silicon carbide. The C/C-SiC brake composites exhibited good mechanical properties. The value of flexural strength and compressive strength could reach 160 and 112 MPa, respectively. The impact strength was about 2.5 kJ·m^-2. The C/C-SiC brake composites showed excellent tribological performance, including high coefficient of friction (0.38), good abrasive resistance (1.10 μm/cycle) and brake steadily on dry condition. The tribological properties on wet condition could be mostly maintained. The silicon carbide matrix in C/C-SiC brake composites improved the wear resistance, and the graphite played the lubrication function, and right volume content of graphite was helpful to forming friction film to reduce the wear rate. These results showed that C/C-SiC composites fabricated by warm compacted-in situ reaction had excellent properties for use as brake materials.     

A study of the mechanical behaviour on fibre reinforced hollow microspheres hybrid composites

This paper presents the results of an investigation into the effects of hollow glass microsphere fillers and of the addition of short fibre reinforcements on the mechanical behaviour of epoxy binding matrix composites. Properties like flexural stiffness, compressive strength, fracture toughness and absorbed impact energy, were studied. The specimens were cut from plates produced by vacuum resin transfer moulding having a microsphere contents of up to 50% and with fibre reinforcement up to 1.2% by volume. The tests performed with unreinforced composites show that flexural and compressive stiffness, maximum compressive stresses, fracture toughness and impact absorbed energy decrease significantly with increasing filler content. However, in terms of specific values, both flexural and compressive stiffness and impact absorbed energy increase with microsphere content. The addition of glass fibre produces only a slight improvement in the flexure stiffness and fracture toughness, while increasing significantly the absorbed impact energy. In contrast, the addition of a small percentage of carbon fibres produces an important improvement in both fracture toughness and flexure stiffness, when hybrid composites with 0.9% carbon fibre are compared to unreinforced foam, but did not improved absorbed impact energy.     

Carbon/Carbon Composite Friction Discs for Aerospace

Carbon/carbon friction discs are produced at Newmet Composites (a division of New Metals & Chemicals Ltd.) for flap jam systems in airplanes. They offer excellent mechanical and friction properties. New carbon/carbon composite grades have been developed at Newmet Composites during the last few years. Another material that is used for this applications is bronze. Different material grades and different designs are compared in this paper. The key‐properties discussed are compression strength, flexural strength and friction behaviour. The friction tests were simulating the friction behavior during the application of such discs. Compression tests were made to define the possible application: For the application in the flap jam system the compression strength has to be 207 MPa at the minimum, for other applications this is not necessarily required. A test described briefly in this paper was developed for flexural strength. The flexural strength is not very important during the application, but important when the discs are being handled and built in. It could be shown that both production parameters and design have a significant influence on the performance of carbon/carbon friction discs. These results are needed to define further applications for these materials. Finally the material carbon/carbon is briefly compared with alternative materials.     

高强隔热刚玉-镁铝尖晶石-莫来石多孔陶瓷材料的制备

以氧化铝、石英粉和电熔镁砂为主要原料,以纸浆废液为结合剂,通过原位反应烧结制备复相高强隔热陶瓷,研究MgO添加量对所制备多孔陶瓷的显气孔率、抗折强度、耐压强度和抗热震性能的影响。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和电子万能试验机对材料的物相组成、显微结构和力学性能进行表征,并对多孔陶瓷的显气孔率和抗热震性能进行测试。结果表明:5%(质量分数)电熔镁砂与氧化铝、石英粉在1450℃下原位反应烧结3h可制备得到刚玉-镁铝尖晶石-莫来石多孔复相陶瓷,耐压强度达270.25MPa,抗折强度超过45MPa,同时显气孔率达26.46%,常温导热系数为1.469W·m^-1·K^-1,隔热性能良好,且3次热震后的残余抗折强度保持率超过27%,是极具应用前景的工业窑炉内衬材料。其中MgO含量变化会直接影响该多孔陶瓷三相组成、相形态、气孔孔径及分布,使得多孔陶瓷抗折强度、耐压强度和抗热震性能呈现非单调变化的规律。     

Mechanical behaviour of polymer concrete systems

The mechanical behaviour of epoxy and polyester polymer concrete systems was studied under different loading conditions at various temperatures, resin content, and glass fibre content. While polymer content varied between 10 and 20% of the total weight of polymer concrete, the fibre content was limited to 4% by weight. The temperature was varied between 22 and 110°C, depending on the glass transition temperature of the resin. Compared to vibration, the compaction method of preparation reduces the void content and enhances the strength and modulus of polymer concrete. The compressive and flexural strength and stiffness of the polymer concrete systems increase up to a certain limit of polymer content at which they exhibit maximum strength and stiffness. They subsequently decrease or remain almost constant with further increase in polymer content. The strength and stiffness of polymer concrete are very much dependent on the temperature. The stiffness model, based on inclusion theory, yields satisfactory results for the three-phase polymer concrete. Using this model, the compression and flexural modulus of polymer concrete can be predicted from the properties of the constituents and their composition. Incremental strength and stiffness models developed in this study are effective in predicting the increase in strength and stiffness of glass-fibre-reinforced polymer concrete.     

T15 and M2-HSS reinforced with carbides for use in hazardous atmospheres and coal mining

Not all cutting materials can be used under hazardous atmospheres which can be found, for instance in coal mines. Certainly, this rock is brittle and amongst the diffent cutting materials, it is possible to use sintered high speed steels (HSS) for disc cutters. Their lower cost and better ductility compared to cemented carbides are advantages in considering their use for cutting applications.This article shows the characteristics of two high speed steels (T15 and M2) with 10% carbide additions (Me=Cr, Mo, Ti, W or V) sintered at 1180°C in a nitrogen base atmosphere for 30 minutes in order to evaluate this manufacturing process as an altermative to vacuum sintering, and the influence of carbide addition. In addition to mechanical properties (hardness and flexural strength) and wear behaviour, the microstructure and evaluation of incenditivity to cause explosion due to mechanical sparks were also tested under several hazardous atmospheres. A method for testing the potential of different materials to ignite hazardous gas has been developed based on rock-on-material friction behaviour in a rotating-wheel test rig.     

Thermal shock behaviour of angle-ply and woven dense ceramic-matrix composites

The behaviour of two Nicalon/calcium aluminosilicate ceramic composite laminates (a (±45°)_3s and a plain-weave woven) under conditions of thermal shock has been studied. Test specimens heated at various temperatures were quenched into room-temperature water. This was followed by detailed damage characterisation. In addition, post-shock mechanical properties were assessed by tensile tests (for the woven laminate) and flexural tests (for both laminates). Both materials were found to have comparable thermal shock resistance. Crack morphologies comprised matrix cracks of various orientations that exhibited similar characteristics to those described for thermally shocked cross-ply laminates with the same constituents, but cracking was found to be less widespread in the woven laminate. Fibre breaks were also detected on the woven material when high-temperature degradation of the fibre–matrix interface was present. A gradual reduction in properties (stiffness, proportional limit stress, fracture strength) of thermally shocked specimens was identified, which began at larger shocks than those at which thermal shock damage initiated. This was attributed to the extension of some matrix cracks into the bulk of material.     

Modelling impact response of agglomerated cork

Cellular materials have been intensively used in engineering applications where a good energy absorption capability is a desired feature. Cork is a natural cellular material capable of absorbing considerable amounts of energy. When compared to synthetic cellular materials, cork also appears as a sustainable alternative, once it is fully recyclable. The purpose of this work is to simulate cork’s compressive behaviour when subjected to impact, including the material’s relaxation after dynamic compression. This study comprises experimental and numerical tests at quasi-static and dynamic strain rates under axial compressive loading. Numerical simulations are performed using Finite Element Analysis, and the material model developed is validated against experimental results. After validation, a dynamic test resorting to a drop tower is carried out successfully validating the model and representing adequately cork’s mechanical behaviour under dynamic compressions.     

Poly(P‐Phenylene Terephthalamide) Fibers Reinforced with Ultrathin Ceramic Coatings

The poly(p‐phenylene terephthalamide) (PPTA) fibers are engineering polymer materials with high strength and stiffness, lightweight, and outstanding fatigue characteristics. However, these materials exhibit drawbacks, namely, anisotropic mechanical strength along the tensile and compressive directions. In particular, they show low compressive strength, and mismatched thermal expansion as well as moisture uptake and oxidative stability along the axial and radial directions. Here, the authors describe a hybrid material approach by integrating ultrathin ceramic coatings (alumina or silica) onto PPTA fibers to enhance their compressive modulus by 2.5 times. In addition, these ceramic coating improve the energy absorption, thermal conductivity, and chemical stability of PPTA fibers, while their flexibility and lightweight are preserved. This strategy provides a new route for the preparation of high performance polymer fibers for advanced engineering applications.

     

Surface nitridation of Al2O3 based composite by N2-HIP post-treatment

Surface nitridation of Alumina based composites reinforced with silicon carbide particles and/or whiskers has been studied. The composites processed by hot-pressing were post-treated by HIP process at 1650–1750°C under 150 MPa of nitrogen gas pressure. X-ray diffraction (XRD) analysis indicates that Alumina and silicon carbide on the surface of the composite are converted to aluminum nitride and silicon nitride, respectively, during the post-treatment. Examinations of surface nitrided layer by scanning electron microscopy (SEM) suggest that grain size can be significantly affected by post-treatment condition. Flexure tests indicate that strength increases significantly by the post-treatment. It is discussed that the improvement of mechanical properties included two parts: one came from the densification of sample, the other came from the surface nitrided layer. Specially, the residual compressive stress plays a key role on the improvement of the flexural strength.     

炭纤维增强C/SiC双基体复合材料的制备及性能(英文)

以针刺炭纤维整体毡为预制体,联用化学气相沉积法与熔融渗硅法制得炭纤维增强C/SiC双基体(C/C-SiC)复合材料;研究了C/C-Si材料的显微结构、力学性能和不同制动速度下的摩擦磨损性能及机理。结果表明:C/C-SiC材料具有适中的纤维/基体界面结合强度,弯曲强度和压缩强度分别达240MPa和210MPa,具有摩擦系数高(0.41～0.54),磨损小(0.02cm3/MJ),摩擦性能稳定等特点.随着制动速度提高,C/C-Si材料的摩擦磨损机制也随之变化:在低速制动条件下主要表现为磨粒磨损;中速时以黏着磨损为主;高速时以疲劳磨损和氧化磨损为主。     

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.     

成型温度对多孔SiC陶瓷性能的影响

以包混工艺合成了核-壳结构的先驱体粉体,并引入少量Al<,2>O<,3>,SiO<,2>和Y<,2>O<,3>作为复合添加剂,通过模压成型、炭化和烧结工艺制备了多孔碳化硅陶瓷;研究了成型温度对样品的孔隙率、密度、热膨胀系数、抗弯强度和热震性能的影响.结果表明:成型温度对多孔碳化硅陶瓷的孔隙率、密度、抗弯强度及热震性能均...     

The effect of filler loading and process route on the three-point bend performance of waste based composites

The three-point bend behaviour of polyester resin composites loaded with high volume fractions of recycled waste materials has been investigated to determine the effect of composition and processing route on performance.

Flyash powder and quarry waste were chosen as candidate fillers. Fillers were added either separately or combined. Three-point bend specimens were manufactured by conventional gravity mould casting, by degassing prior to casting or by vibration moulding. The addition of filler to the resin matrix resulted in a steady reduction in ultimate flexural strength from approximately 85 MPa for the pure resin to approximately 40 MPa for 50% filled material. As filler levels were increased above this level, the strength rapidly decreased. A corresponding increase in flexural stiffness with increasing filler amount was also evident.

For a given amount of filler, flexural strength decreased with increasing particulate filler size. The flexural modulus appeared to be unaffected.

The effect of matrix reinforcement on the performance of heavily filled (>75% by volume) polyester resin is also presented. Matrix reinforcement resulted in the production of high strength/high modulus materials with filler contents up to 75% and it is envisaged that these filler ratios can by further increased without a loss of flexural strength.     

Interaction between cyclic loading and residual stresses in titanium matrix composites

Metal matrix composites are gaining popularity for applications where high performance materials are needed. Titanium matrix composites (TMCs) continuously reinforced by silicon carbide fibres are under development for applications in aeroengines. Their use in blades, rings and shafts promises a significant weight reduction and performance improvement due to their high specific strength and stiffness. To obtain the whole capabilities of the material not only advanced processing techniques but also post-processing treatments are necessary. A detailed analysis of the residual stress development during cyclic loading leads to the necessity of residual stress modifications to optimise the fatigue behaviour of TMCs. Since the aerospace industry requires high reliability of the materials used, models for predicting failure and life time are of special interest. Predictive models based on the properties of the single constituents of the composite are most suitable to reduce the number of experiments and to develop methodologies to improve specific mechanical properties. Nevertheless, both experiments on the single constituents as well as on the composite are necessary to validate the model. A previously developed rheological model is used to assess different post-processing procedures to improve the fatigue behaviour of a titanium matrix composite. The usage of the model and experiments on the system SCS-6/Ti-6Al-2Sn-4Zr-2Mo are presented.     

Effect of thermal cycling on whisker-reinforced dental resin composites

The mechanical properties of dental resin composites need to be improved in order to extend their use to high stress-bearing applications such as crown and bridge restorations. Recent studies used single crystal ceramic whiskers to reinforce dental composites. The aim of this study was to investigate the effects of thermal cycling on whisker-reinforced composites. It was hypothesized that the whisker composites would not show a reduction in mechanical properties or the breakdown of whisker–resin interface after thermal cycling. Silicon carbide whiskers were mixed with silica particles, thermally fused, then silanized and incorporated into resin to make flexural specimens. The filler mass fraction ranged from 0% to 70%. The specimens were thermal cycled in 5 °C and 60 °C water baths, and then fractured in three-point bending to measure strength. Nano-indentation was used to measure modulus and hardness. No significant loss in composite strength, modulus and hardness was found after 10⁵ thermal cycles (family confidence coefficient=0.95; Tukey's multiple comparison test). The strength of whisker composite increased with filler level up to 60%, then plateaued when filler level was further increased to 70%; the modulus and hardness increased monotonically with filler level. The strength and modulus of whisker composite at 70% filler level were significantly higher than the non-whisker controls both before and after thermal cycling. SEM revealed no separation at the whisker–matrix interfaces, and observed resin remnants on the pulled-out whiskers, indicating strong whisker–resin bonding even after 10⁵ thermal cycles. In conclusion, novel dental resin composites containing silica-fused whiskers possessed superior strength and modulus compared to non-whisker composites both before and after thermal cycling. The whisker–resin bonding appeared to be resistant to thermal cycling in water, so that no loss in composite strength or stiffness occurred after prolonged thermal cycling.     

Deformation rate dependence of mechanical properties of epoxy resin at cryogenic temperatures

Effects of deformation rate on the mechanical properties of epoxy resin used in superconducting magnets have been studied at cryogenic temperatures. Compressive and flexural tests were made to reveal the mechanical behaviour. In the case of compressive tests, the increase in the deformation rate caused on increase of elastic modulus and a decrease of breaking stress and strain. In the case of flexural tests, different results in breaking stress were obtained. The results indicate that the following two problems must be elucidated for practical use of polymers in magnets, ie (i) impact strength of the polymers, (ii) the stress condition applied to the polymers in the magnet.     

Ultra‐thin carbon/silicon carbide composite bipolar plate for advanced fuel cells

The first cut results on the development of ultra‐thin, low gas permeable, easily machineable, high electrical conductivity and high mechanical strength bipolar plate made up of carbon reinforced ceramic matrix are reported for the strategic application. Short carbon fiber reinforced silicon carbide matrix composite is fabricated by chopping continuous carbon fibers into discrete length, exfoliating and dispersing the exfoliated carbon fibers in silicon carbide powder and finally hot‐pressing to make the composite. Three compacts containing exfoliated carbon fiber contents of 20, 30, 50 vol. % in silicon carbide matrix are prepared and characterized for electrical, thermal, gas permeability, density, and mechanical properties. The composite plates with exfoliated carbon fiber vol. % of 50, offer excellent electrical conductivity, flexural and compressive strengths and gas permeability of 2.2 × 10^‐7 cm^‐3 cm^‐2 s^‐1. Carbon/silicon carbide plate shows 37.5 % and 4.7 % lower volume and weight, respectively on comparing with the best reported data of carbon/polymer composite plate. Competency of the material for bipolar plate fabrication is tested and found that the ceramic carbon composite may open up the new horizon for the fabrication of ultra‐thin bipolar plates for strategic applications.     

Evaluation of the performance of recycled textile fibres in the mechanical behaviour of a gypsum and cork composite material

Given the need for using more sustainable constructive solutions, an innovative composite material based on a combination of distinct industrial by-products is proposed aiming to reduce waste and energy consumption in the production of construction materials. The raw materials are thermal activated flue-gas desulphurization (FGD) gypsum, which acts as a binder, granulated cork as the aggregate and recycled textile fibres from used tyres intended to reinforce the material.This paper presents the results of the design of the composite mortar mixes, the characterization of the key physical properties (density, porosity and ultrasonic pulse velocity) and the mechanical validation based on uniaxial compressive tests and fracture energy tests. In the experimental campaign, the influence of the percentage of the raw materials in terms of gypsum mass, on the mechanical properties of the composite material was assessed.It was observed that the percentage of granulated cork decreases the compressive strength of the composite material but contributes to the increase in the compressive fracture energy. Besides, the recycled textile fibres play an important role in the mode I fracture process and in the fracture energy of the composite material, resulting in a considerable increase in the mode I fracture energy.     

An investigational analysis of W-shaped engineering hybrid fiber composites utilizing steel and boron carbide

As engineering demands increase, ordinary conventional materials cannot satisfy requirements in the 21st Century. Hybrid ceramic/metal matrix engineering composites introduce original design concepts which surpass criteria and enhance design standards, particularly when utilized within civil and thermal engineering applications. The selection of boron carbide, B₄C, in civil engineering applications displays unique property values, including flexural rigidity and stresses, and when infused with select A992 structural steel allows secondary opportunities for complex and diverse engineering applications. This article investigates an overview of boron carbide fibers and its steel matrix (SB₄C) with conventional steel, focusing on flexural rigidity and stresses. The flexural rigidity of laminated boron carbide fibers with W-shaped structural steel members is also observed. A civil engineering application based on flexural rigidity of a basic and a laminated SB₄C member is discussed as well. The investigation reveals that the SB₄C combination displays greater strength and stiffness values than conventional steel construction.