Переменные параметры «упругости» нелинейно деформируемой трансверсально-изотропной среды

Composite materials are engineered materials made from two or more constituent materials. They have significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure. The advantage of composite material is that they exhibit the best qualities of their components or constituents and often some qualities that neither constituent possesses. The properties that can be improved by forming a composite material are strength, stiffness, corrosion resistance, wear resistance, weight, thermal insulation, thermal conductivity, etc. Composite materials can be classified and characterized into four commonly accepted types; (1) fibrous composite materials that consist of fibers in a matrix, (2) laminated composite materials that consist of layers of various materials, (3) particulate composite materials that are composed of particles in a matrix and (4) the combination of some or all the first three types (Jones, 1999). According to the matrix phase the composites are divided into three groups; (1) metal matrix composites (MMCs), (2) polymer matrix composites (PMCs) and (3) ceramic matrix composites (CMCs). Ceramic materials in general have very attractive properties e.g.: high strength and high stiffness at very high temperatures, chemical inertness and low density. In the presence of flaws (surface or internal) they are prone to catastrophic failures. Ceramic materials can be toughened by incorporating fibers and thus exploit the attractive high-temperature strength and environmental resistance of ceramic materials without risking a catastrophic failure (Chawla, 1987). According to the basics written above, a monolithic silicone carbide (SiC) was used as a matrix phase, which has been recognized as one of the most promising structural materials for many thermo-mechanical applications because of its excellent hightemperature strength and modulus, good oxidation resistance, high hardness, low specific weight and low density (Xin-Bo & Hui, 2005; Xin-Bo et al., 2000; She et al., 1999). The problem with monolithic SiC is its low thermal shock resistance, which leads to cracking and catastrophic failure of the material. Thermal shock resistance and crack propagation can 6

Production of electric power by nuclear power plants (NPP) in the world and in Russia accounts for about 17%. Much attention is currently paid to safe NPP operation and to enhancement of their reliability. Present-day nuclear power plants with high-temperature gas-cooled rectors require development and application of new composite materials capable to withstand high temperatures and mechanical stresses. Ceramic composite materials where whiskers of heat-resistant chemical compounds are used as reinforcement fibers look promising for those purposes. The paper investigates and analyses the opportunity of applying whiskers as reinforcement fibers for heat-resistant composite ceramic building materials. Studies revealed that whiskers of silicon carbide and aluminium nitride are resistant towards high temperature heating without notable change in their chemical composition. It was found out that mono crystals of silicon carbide have higher mechanical strength owing to lack of defects in its structure. Linear heat expansion factors of silicon carbide that are needed for thermo-chemical calculations of composite materials on its base were determined.

In this study, a new composite ceramic material using a red clay matrix with different amount of clinker from the cement industry has been developed. The aim is to valorize some natural resources such as red clay and sub-products from the cement industry as clinker in order to develop new materials for industrial and/or catalytic uses. Raw materials were grounded in order to reduce the particle size and obtain a homogeneous slip. The samples were mixed and compressed into pellets and undergo a heat treatment up to 1100℃. Geotechnical characterization has been carried out. Firing proprieties (shrinkage, water absorption, and mechanical resistance to the inflection) were measured. The composition of the ceramic material was investigated by X-ray diffraction, XRF, SEM and EDS methods. The incorporation of clinker in the ceramic composite material up to 50 wt% exhibits good behaviors (physical and mechanical proprieties) and can be used as a ceramic product.

Monolithic ceramics and continuous fiber reinforced ceramic composites are being developed for use in high temperature applications such as combustor liners in gas turbines, thrust deflectors for jet engines, and thruster nozzles. Ceramic composite materials possess the high temperature resistance properties of ceramics, but have better creep and cyclic properties. However, the properties of these materials change somewhat with time at service temperatures, i.e., their material state changes as a function of service conditions and history. The authors have developed a methodology for representing and combining the effects of high temperature material state changes in CMCs, along with changes in applied stress / strain conditions during service, to estimate remaining strength and life of ceramic composite materials and components. Fatigue, creep rupture, and time dependent deformation are combined by a strength metric in integral form to create a time-resolved, point-wise estimate of current remaining strength and life in material elements. Application of this methodology in discrete element representations of mechanical behavior of structural elements with nonuniform stress / strain states has been implemented.

New composite ceramic materials enable to improve mechanical properties and various performances more than monolithic ceramic materials. Generally, composite ceramic materials include more than two different materials, in addition, more than two crystal structures in case of α and β crystal phase composite Si3N4 material in this research. Composite ceramic materials enable to get various different characteristics that show excellent properties, not only mechanical properties but electrical properties, resistance to oxidation and wear. Properties improvement develops many new applications with superior performance more than conventional materials. In this research, we have developed various ceramic reinforced composite, based on Al2O3 and ZrO2 ceramics with carbide and nitride particles or whisker addition. Farther more we have developed α and β crystal phase composite Si3N4 material by researching the sintering additives stoichiometric ratio and sintering condition. Finally we succeeded in applying ceramic composite materials to various industrial parts, for example, Al2O3-TiC thin magnetic slider substrate, Al2O3-SiC whisker based cutting tool, Si3N4 squeezing roll and wear parts, ZrO2-WC ceramics punch and die for high speed pressing.

Effects of sintering parameters on microstructure, graphene structure stability and mechanical properties of graphene reinforced Al2O3-based composite ceramic tool material

Chapter 1 - Overview of additive manufacturing technology and materials

Spark plasma sintering and hot compaction methods were used to obtain experimental samples of a composite material of the SiC‒SiCw system with various modifying additives (AlN, B4C, HfB2, Y2O3, Al2O3, Si3N4). The effect of the modifying additives on the sintering process, physicomechanical, and thermal properties of the ceramic composite material was examined. The introduction of the modifying additives lowered the sintering temperature of silicon carbide produced by the hot compaction method by 200°C and that formed with spark plasma spark sintering by 300‒450°C as compared with the sintering temperature of silicon carbide without additives.

Innovative composite materials research at the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy

When boron fibres are combined with an organic matrix, such as an epoxy resin, a high-performance composite structure is created. This study investigates the surface chemistry of plasma- and organosilane-treated boron fibres with the key aim to improving the adhesion properties between the boron fibre and the epoxy matrix. Optimisation of this interfacial region plays a critical role in influencing the mechanical behaviour of composite materials and has considerable industrial applications in the aerospace and manufacturing industries. The surface chemistry of a model boron surface and boron fibres was monitored using a combination of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Initial investigation of the as-received fibres showed the presence of silicone contamination on the fibre surface, which would affect adhesion. Removal of this contaminant through solvent cleaning and plasma oxidation provided an ideal surface for attachment of the organosilane adhesion promoter. A model for the interaction of the organosilane with a boron surface is proposed. The pull-out strength of boron fibres, with different surface treatments, embedded in the epoxy resin was measured using a custom designed adhesiometer. Compared with as-received boron fibres, a 6-fold improvement in the apparent interfacial shear strength was achieved for the organosilane treated fibres. Optical microscopy was used to determine the failure mechanisms between the fibre and epoxy resin. Typically, as the surface treatment improved adhesion, the locus of failure changed from the boron–epoxy interface to failure within the epoxy and ultimately fibre breakage.

Investigation of a new type of composite ceramics for thermal barrier coatings

A versatile, automated, laser-based system, capable of producing complex threedimensional
\nshapes of ceramic and ceramic composite materials, through either controlled layer
\nablation or solid freeform fabrication, is currently under development. The system comprises
\na 1.2 kW C021aser, positioning system, beam scanner, non-contacting positioning sensor, beam
\nconditioner and CAD/CAM system. This paper reports progress in relating machine parameters
\n(scan rate, feed, beam power and polarization) to process measurables (material removal rate
\nand surface roughness), and demonstrates the potential for rapid prototyping and direct
\nmanufacturing of: (a) rotationally symmetric components based on ablative ceramics such as
\nSi3N4 and (b) graphite fuel cell plenums

Simulation and analysis of sintering warping and thermal stress for a cermet half-cell of solid oxide fuel cells

Composite metallic materials can be build using photonic band gap materials with different lattice constants, these new structures showing wider forbidden frequency bands. The insertion of lattice defect in one or more materials allows the opening of multiple frequency pass band filters in these forbidden bands. The transmission rate and the width of these filters may be adjusted with the number of defects and the geometrical parameters of the lattice. This concept may be used at any scale to realise mirrors and pass band filters at microwave or infrared frequencies.KeywordsPhotonic CrystalDefect LatticeDefect ModeTransmission PeakTransmission RatioThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

This study presents a simulation methodology to choose the optimal material combination before constructing a ceramic‒metal composite joint. Two types of joint assemblies/structures designed with and without pores and eight material combinations are tested. The finite element discretization of the model is implemented using Abaqus. The effect of thermal stress is functionally evaluated by Von Mises Stress (VMS) and average volumetric stress as a decision parameter. The joint assembly with Al 2 O 3 /Ag‒Cu‒Ti/Kovar composite material is found to have a relatively larger limit to get fractured. The thermal strain rate for optimal material combination is 3.77 × 10 −6 K ‒1 (with pores) and 6.11 × 10 −6 K ‒1 (without pores), respectively. The porous joint structure's average thermal stress is (∼30%‒50%) lower than the non‐porous joint structure. The analysis concludes that pores do not always deteriorate joint performance. An empirically fit equation is derived to estimate the VMS value for any pore's shape, size, location, porosity, and material properties. The equation can be used to predict the VMS value for any ceramic‒metal composite material combinations. An empirical linear equation is also derived to predict effective coefficient of thermal expansion as a function of microstructure (shape, size, location, and porosity) and material type (effective molecular mass).