Carbon-carbon Composite Materials Research Articles

Improving the antifriction properties of the housing-rotor coupling in axial turbomachines

The article discusses the frictional interaction of carbon-carbon composite material on steel. Antifriction properties and wear resistance of the material under dry friction at speeds up to 100 m/s are investigated. The effect of velocity and contact pressure on the friction coefficient and wear resistance of a carbon composite is analyzed. The regularities of the change in the coefficient of friction are determined depending on the load-speed factors. The assumption is substantiated that the high thermal stability of the carbon composite, its low hardness, good antifriction properties and high wear resistance allow the material to be used in friction units operating at very high speeds and temperatures. In order to improve the reliability and reduce gas flows in axial turbomachines, on the basis of the study carried out, it is recommended that instead of heat-resistant coatings, a lining of the gas duct casing should be made of carbon composite.

Calculation of strength, rigidity, and stability of the aircraft fuselage frame made of composite materials

Carbon-carbon composite materials (CCCM) are characterized by high heat resistance and thermostability for which they, in most of their physical and mechanical characteristics, can be attributed to the most promising materials. Approximately 81% of all carbon-carbon composite materials are used for the manufacture of brake rotors for aircraft, 18% – in space rocket technology, and only 1% – for all other areas of application. This study discusses calculations of the strength, rigidity, and stability of a frame made of carbon-carbon composite materials. It is known that the strength of CCCM based on high-strength carbon fibers is higher than the strength of a composite material based on high-modulus carbon fibers obtained at various processing temperatures. The stress-strain behaviour (SSB) of the material is carried out. Among the special properties of CCCM are low porosity, low coefficient of thermal expansion, maintaining a stable structure and properties, as well as product dimensions.

Bearing capacity of a threaded pair made of spatially reinforced carbon-carbon composite materials at high temperatures

The bearing capacity of a threaded pair made of spatially reinforced carbon-carbon composite materials (CCCM) with a 4DL reinforcement scheme in the temperature range from 20 to 2500 °C is experimentally determined. Recommendations are given for the design of CCCM threaded joints for operation at high temperatures. Keywords: carbon-carbon composite material, threaded joint, limit load, bearing capacity, threaded pair, high temperature. mn@bmstu.ru

THE INVESTIGATIONS OF A PECULIARITIES OF PYROCARBON GAS PHASE DENSIFICATION OF POWDERS OF THE CATALYTIC CARBON FORMATIONS (CCFs), OBTAINED ON NICKEL

Investigations on gas-phase densification of the catalytic carbon formations (CCFs), obtained on nickel, using the method of radially driven pyrolysis zone were carried out. Straight dependence of the brittle strength of the CCFs, bonded with pyrocarbon (CCFBPyC), from the CCFs morphology, was shown. It was determined, that the result of decreasing of an amount of fibrous, fine-grained CCFs component is the increasing of strength of the pyrocarbon matrix . For the first time, carbon/carbon composite materials (CCCM ) without cracks, which contain refined or not-refined from nickel, carbon nanomaterials (CNM), were obtained.

Определение коэффициентов трения в резьбовых соединениях из углерод-углеродных композиционных материалов

Experimental studies were carried out to estimate the friction coefficients for a screw-nut threaded pair made of spatially reinforced carbon-carbon composite materials (CCCM). Quantitative values were obtained for the thread friction coefficient and nut end friction coefficient. The ultimate screw-in torque for the CCCM threaded pair was determined, and its failure mode at a destructive screw-in torque was established. The laboratory tests were carried out to measure the tightening force. The nut screw-in torque was measured using a torque wrench.

Experimental study on temperature field of civil airplane wheel and brake

In this paper, a set of the temperature field experimental method of civil aircraft wheel and carbon-carbon composite heat sink material is established. The heat absorption performance of the carbon-carbon composite heat sink and the heat dissipation performance of the wheel structure were characterized by this method. Using this method, the temperature field experiment of the wheel and brake device of a civil aircraft is carried out, and the test working conditions of the temperature field of the civil aircraft are established, the curves of temperature change with time during normal braking, taxiing braking and cooling are obtained, and the maximum temperature and heat dissipation characteristics are obtained.

Structural failure criterion for spatially-reinforced carbon-carbon composite materials

This paper defines the structural strength criterion for 4DL-reinforced carbon-carbon materials. For this scheme, fiber reinforcement consists of four groups of reinforcing elements, three of them are located in parallel planes with the angles of 120° between them and the fourth one is normal to them. The paper addresses the first failure of the material corresponding to its yield stress, in this point, one of the material components deviates from linear elastic behavior. A composite material is considered to be non-uniform structurally and consists of a matrix and reinforcing elements, rods. Those rods, in their turn, represent a unidirectional composite. To analyze the stress-strain state of individual components of the material, a three-level elastic model is built that uses the analytic approach at the micro level, while at higher levels it uses the finite element method. For numerical calculations, a structural cell of the material is taken. The boundary conditions provide small to negligible influence of the edge effects, thus simulating the behavior of the infinite volume of the material. For the material components, local strength criteria are introduced, where the fields of the criterion quantities are averaged over the volume of the structural cell. The strength surface of the material that corresponds to its first failure is obtained, and the conclusion is made that the suggested criterion provides a reasonable agreement with the available data on the typical carbon-carbon composite characteristics. Based on the calculated dependencies of the material’s yield stress on the load direction, a procedure is suggested to identify the model parameters based on the material failure behavior analysis using standard tensile and compressive tests. Estimated discrepancies between the results calculated using the suggested criterion and those obtained using the limiting stress criterion for biaxial stress states are given. It is shown that the discrepancy may reach tens of percent and in some cases the material strength increases in comparison with that in the uniaxial stress state. The results are subject to verification tests in order to verify the model for advanced spatially reinforced carbon-carbon composite materials.

Corrosion of Ceramic and Carbon-Based Materials in FLiNaK

Molten salt nuclear fast nuclear reactor (MSNFR) is one of the prospective design in frame of Generation IV concept. This technology is also required for reprocessing of spent nuclear fuel (SNF) in molten salts to extract valuable components. Recycling SNF consists of extraction uranium and plutonium with the disposal of minor actinides and fission products. These stages need the materials that retain their corrosion and mechanical properties for long time under the influence of high temperatures, radiation fields and contact with molten salts. Various steels and alloys were widely studied to assess their use under such extreme conditions. Alternative materials include ceramics, composite and carbon materials, which have high corrosion resistance in various media and can be used up to 1000 °C.In the present work the corrosion and mechanical properties of nitride ceramics (Si3N4 and BN) and carbon-based materials (carbon-carbon composite material (C/C) and high-density carbon) were studied in a molten mixture of lithium, sodium, and potassium fluorides (FLiNaK) in the temperature range of 550–750 °C under inert atmosphere. Corrosion tests were performed under static conditions, and the duration of each test was 100 h to enable the comparison of the experimental data.It was found that carbon-containing materials (C/C and high-density carbon) showed high corrosion resistance in the melt. C/C samples had lower corrosion rates (less than 0,1 mm/year in the entire temperature range), while the high-density carbon showed better mechanical properties. The main disadvantage of these materials is their impregnation by molten salt due to relative high porosity. However, C/C composite and high-density carbon are promising structural materials for salt media based on FLiNaK in the selected temperature range.Tested nitride ceramics (BN, Si4N3) demonstrated relatively low corrosion resistance in fluoride systems compare to carbon-containing and metallic materials. The corrosion rates of these materials in FLiNaK exceeded the value of 1 mm/year. The plastic properties of nitride ceramics were also poor. Possible application of such materials for MSNFR and SNF reprocessing is under further investigation.

Structure and Properties of a Silicide-Carbide Protective Coating on Carbon-Carbon Composites

Heat resistance and microstructure properties of a prospective multilayer protective coating on carbon-carbon composite materials are studied. Thermomechanical compatibility of a coating with base material, its thermal stability, thermal shock and cracking resistance are evaluated.

Calculation and experiment approach to predicting the properties of C/SiC and SiC/SiC composites

One of the current trends in aviation and space technology is higher flight speed. An increase in flight speed means an increase in the temperature of the aircraft components and tougher requirements for the physical and mechanical characteristics of the materials used. As metals are reaching their limits, heat-resistant non-metallic materials are attracting more and more attention. Of all heat-resistant non-metallic materials, the most appropriate for this purpose are monolithic ceramic materials, carbon-carbon and ceramic-matrix composite materials. This paper proposes an approach to predicting the mechanical characteristics of ceramic composite materials based on experiment and numerical simulation of the material microstructure. Multi-stage impregnation and pyrolysis (PIP) method was used to manufacture C/SiC and SiC/SiC ceramic samples, which were later subjected to tensile testing and 4-point bend testing. The results of numerical modeling and the results of experiments were compared, and the mechanical properties of the materials were determined.

The effect of humidity on the tribological behavior of the carbon-carbon composite in brakes

The article is devoted to the study of the humidity effect on the antifriction properties of a carbon-carbon composite material under the brake-applied mode. The effect of friction coefficient reducing due to the hygroscopic properties of this carbon composite is justified. The change in the friction coefficient and the composite structure during braking is investigated. In a macro scale it is shown that the structure of the samples working surface is isotropic both in the initial condition and after friction, which is due to the specific location of the fibrous carbon filler (reinforcing frame) in the volume of this carbon-carbon composite material. Based on the theory of errors, metrological assurance for evaluating the reproduction of experimental data was performed. Based on the obtained quantitative data on the reduction of the friction coefficient and the “drying” time of wet friction surfaces, practical recommendations are defined to ensure the effectiveness of vehicle braking arrangements.

EXPERIMENTAL STUDIES OF HEAT AND MASS TRANSFER FROM TIP MODELS MADE OF CARBON-CARBON COMPOSITE MATERIAL (CCCM) UNDER CONDITIONS OF HIGH-INTENSITY THERMAL LOAD

Carbon-carbon composite materials are characterized by high heat resistance and thermostability for which they, in most of their physical and mechanical characteristics, can be attributed to the most promising materials. Approximately 81% of all carbon-carbon composite materials are used for the manufacture of brake rotors for aircraft, 18% – in space rocket technology, and only 1% – for all other areas of application. While the need for composites for rocket and space technology is constantly decreasing – the volume of production of brake disc rotors for aircraft is steadily growing, and therefore research on the properties of carbon-carbon composite materials (CCCM) under conditions of high-intensity thermal loading is extremely urgent at the moment. In this paper, we consider a method for introducing silicates and oxides hardening them with the addition of refractory, chemical elements into CCCM. Tests of tips from CCCM were carried out under conditions of high-intensity thermo-force loading. The objectives of the experiment were to obtain scalded forms of the tip model and to record the temperature on the surface during the action of a jet flowing out of the nozzle of the propulsion system (PS). The tip of the CCCM is blown by means of a propulsion system with a supersonic flow of a highly enthalpy oxygencontaining gas. The results of experimental studies were determined using video recording on the basis of which sequences of frames were obtained on the basis of which the burning forms were built. Using thermal imaging measurements, the temperature field on the model surface was determined during the entire time the supersonic gas flow was exposed to it.

Tribology of carbon-containing materials in the carbon dioxide environment at high temperatures

The work is devoted to high-temperature tribological testing of carbon-containing materials during friction on 40X13 steel in the temperature range from plus 20 to plus 800 ° C in a carbon dioxide environment. The choice of temperature and test environment is due to the prospects of creating spacecraft drives for operation without lubrication in the atmosphere of Venus. Studies have shown that the friction process in a carbon dioxide environment at a temperature of plus 300 ° C reduces the coefficient of friction, so at a load of 0.5 MPa, the friction coefficient is lower by 67%, and at a temperature of plus 600 ° C the coefficient of friction is lower by 38%. At a load of 1.0 MPa and a temperature of plus 300 ° C, the friction coefficient in a carbon dioxide environment is lower by 55%, and at a temperature of plus 600 ° C the friction coefficient is lower by 45%. In the range of operating temperatures from plus 300 to plus 600 ° C at a speed of 0.16 m/s and a load of 0.5 MPa and 1.0 MPa, the friction coefficient does not exceed the value of 0.3. The friction coefficient decreases with increasing load. At a temperature of plus 500 ° C and a load of 0.5 MPa, the coefficient of friction in a carbon dioxide medium is 1.9 times less than the carbon-carbon composite materials in an air atmosphere, and at a load of 1.0 MPa it is 2.1 times less than a carbon-carbon composite materials in the air atmosphere.

CCCM SPECIFIC SURFACE ESTIMATION IN PROCESS OF LOW-TEMPERATURE OXIDATION

The low-temperature oxidation process of carbon-carbon composite materials (CCCM) with a pyrocarbon matrix has been examined. Oxidation at temperatures of 450 to 700 °C is characterized by internal burnout of the carbon phase without a noticeable change in the experimental samples external volume. Oxidation resistance analysis of CCCM structural components was performed. CCCM and carbon fibers specific surface area were estimated by the low-temperature adsorption of nitrogen and krypton using the Brunauer-Emmett-Teller model and the theory of density functional model. Pore size distribution was calculated by the semi-empirical Horvath-Kawazoe method. A significant increase (about 10-15 times) in specific surface area of the composite material, together with a rise in free volume ~5%, was accompanied by total weight loss of about 5%. Specific surface area changes occur as a result of anisotropic etching of carbon fibers surface with the formation of micropores with 0.5–2.0 nm diameter range. Although macropores are formed mainly due to the oxidation of thermosetting binder pyrolysis residue, they do not contribute to the specific surface increase but solely provide access to micropores. Microporosity evolution leads to an increase of structural discontinuity degree and, ultimately, to the loss of matrix-filler contact boundary. As a result, an overall weakening of material mechanical characteristics is to be noted. Thus, oxidative degradation is closely related to the increase in void space. A follow-up study is on-going. In fact, an open question remains, namely whether the oxidative process occurs differently in the micropores of diameter less than 2 nm and how it may contribute to the oxidative stress resistance behavior of CCCM.

INVESTIGATION ON CORROSION PROPERTIES OF CARBON-CARBON COMPOSITES

The corrosion resistance of carbon-carbon composite materials (C–C composites) was studied in a corrosive media of coolant NaF+ZrF4 salt (a model heat-transfer) at 700 °С in the air flow. It has been shown that C–C composite material is resistant to the model heat-transfer even under conditions of critical temperature accident. The main mechanism that leads to the C–C composite corrosion is a mechanism of composite material oxidation due to the contact with the air. The study has evidenced that the C–C composite burn-up rate well correlates with the pyrocarbon matrix content in the composite, the matrix content increase by 2530% results in the composite corrosion resistance increase by a factor of 2–4. So, by developing corrosion-resistant carbon-carbon composites one has a problem of finding an optimum fiber-matrix ratio in the composite. It has been confirmed experimentally that by silication of C–C composites with the use of the methods which were developed in NSC KIPT it is possible to increase the service life of products under simulated accident conditions by a factor of 7–7.5.

Механизм формирования карбидокремниевого покрытия диффузионным методом в кремниевой засыпке на углерод-углеродных композиционных материалах

The pack cementation process, used for obtaining coatings, is described, as a rule, in terms of solid-phase diffusion, which leads to saturation of the near-surface layer of the workpiece with a certain element. This method allows the deposition of a silicon carbide coating on carbon-carbon composite materials, that increases its resistance to the action of high-temperature oxidizing environments. An analysis of the kinetic features of the formation of silicon carbide on a carbon material indicated the difference between this method and the classical diffusion saturation. It turned out that it is necessary to consider additional processes of gas formation that occurs in the powder filling. A mechanism has been proposed, according to which it is possible to transfer silicon through the gaseous reagent SiO, generated in the backfill with the help of oxide additives, like aluminum oxide, which were previously considered inert.

Experimental and Numerical Study of the Formation of Thermophysical Characteristics of Carbon Composite Materials. Part 2. Numerical Simulation of Operability of a Refractory Product Made of Carbon Composite Material

A heating of a carbon-made product and thermophysical properties of a carbon material in the temperature range from 300 to 2,500 K were studied. A discrete-heterogeneous mechanism of heating the surface of a multi-dimensionally reinforced carbon-carbon composite material (CCCM) subject to accelerated heating was revealed. Based on the results of testing carbon materials in the temperature range from 300 to 3,000 K, a numerical stress analysis of the product was performed, in which the arising stress condition was considered to be resultant from constraining the deformation of the heated parts of the product by relatively cold fragments. The safety factor levels were found for different parts of the product. It was shown that an additional increase in thermal strength as part of the combined definition of thermal resistance of CCCM products is associated with high thermal conductivity of 1D-reinforced rods of material structure.

Experimental and Numerical Study of the Formation of Thermophysical Characteristics of Carbon Composite Materials. Part 1. Formation of the thermophysical Characteristics of a Carbon Composite Material

The analysis of a heat transfer mechanism in the bulk of carbon-carbon composite materials was performed. It was experimentally determined that a homogeneous thermal condition is established at a depth of up to twenty structural cells of the composite. A characteristic layered porosity structure of the material formed by crack-like pores was revealed, and the extent of reduction in thermal conductivity upon splitting the samples into parts was determined. It was found that the process of cooling of the hot reinforcement rod in the carbon substance of the composite is less dependent on the effective thermal conductivity in the direction transversal to a bundle of parallel fibers in a 1D-reinforcement rod, and more dependent on the contact thermal resistance along the boundaries of the crack-like pores filled with air having a thermal conductivity of about 0.3 W/(m·K).

Requirements for technical support of measurements of local elastic characteristics of CCCM by indentation method

The paper is devoted to the study of the applicability of the indentation method for determining local properties of the matrix of carbon-carbon composite materials. It is shown that from the point of view of preserving the integrity of the matrix, it is advisable to use an indenter with the maximum possible diameter of spherical blunting. The characteristic values of contact stiffness, which have a significant value, are determined, which imposes restrictions on the components of the power circuit of the indentation device. The laws of changes in the level of stresses in the sample under various conditions, including the friction coefficients in the contact, are obtained. Estimates of the influence of the structural heterogeneity of the material on the measurement results are given, and it has been established that with a rational organization of the experiment, they are negligible.

Estimation of the effective elastic characteristics of carbon composite materials by testing ring-shaped samples under high temperatures

A computational and experimental method is suggested to determine indirectly the elastic properties of carbon composite materials at room temperature up to 2200°C and more. The method involves loading of ring-shaped test specimens through diametrical compression using non-cooled indenters at three points, within the elastic strain range, with ductility measurements. Based on the measured ductility values, shear moduli, as well as the longitudinal and transversal elasticity moduli in the test specimen cutting plane, can be determined by solving the identification problem. Results of experimental assessment of the permissibility of repetitive mechanical and thermal loading of the carbon-carbon composite material are presented. Method tryout with high-density needle-punched composite material is described.