Composite materials - future materials.
After the modern physics of metals has in detail articulated us the reasons of their toughness, strength and its increase, intensive regular working out of new materials has begun. It will reduce, possibly, already in the imaginable future to creation of materials with the strength many times over exceeding its values at usual today of alloys. Thus the great attention will be given to already known gears of quenching of a steel and ageing of aluminium alloys, combinations of these known gears with processes of shaping and numerous possibilities of creation of the combined materials. Two perspective paths open the combined materials strengthened or filaments, or диспергированными firm particles. At the first the most thin high-tensile filaments are entered into an inorganic metal or organic polymeric die from glass, carbon, boron, a beryllium, steels or threadlike monocrystals. As a result of such combination the maximum strength is combined with a high coefficient of elasticity and small tightness. Such materials of the future are composite materials.
Composite material - constructional (metal or nonmetallic) a material in which there are elements strengthening it in the form of fibers, filaments or flakes of stronger material. Examples of composite materials: the plastic reinforced boric, carbon, by glass fibres, harnesses or fabrics on their fundamentals; the aluminium reinforced by fibers of a steel, a beryllium. Combining the volume contents of components, it is possible to receive composite materials with demanded values of strength, hot-resistance, a coefficient of elasticity, abrasive firmness, and also to create compositions with necessary magnetic, dielectric, radio absorbing and other special properties.
1. Types of composite materials
1.1 Composite materials with a metal die
Composite materials consist of a metal die (more often Al, Mg, Ni and their alloys), hardened by high-tensile filaments (fibrous materials) or it is thin the disperse
the high-melting particles which are not dissolved in a base metal (the dispersibly-hardened materials). The metal die links filaments (disperse particles) in a single whole. A filament (disperse particles) plus a sheaf (die), making this or that composition, composite materials have received the title. 2.2. Composite materials with a nonmetallic die.
Composite materials with a nonmetallic die have found wide application. As nonmetallic dies use polymeric, carbon and ceramic materials. From polymeric dies the greatest spreading have received эпоксидная, фенолоформальдегидная and polyamide. Coal dies коксованные or pirocarbon receive from the synthetic polymers exposed pyrolysis. The die links a composition, forming it. Упрочнителями filaments serve: glass, carbon, boric, organic, on the basis of threadlike chips (oxides, carbides, боридов, nitrides and others), and also the metal (wires) possessing high strength and ruggedness.
Properties of composite materials depend on composition of components, their combination, a quantitative ratio and a connection strength between them. Reinforcing materials can be in the form of filaments, harnesses, fibers, ribbons, multilayer fabrics.
The contents упрочнителя in the oriented materials makes 60-80 about. %, in nondirectional (with discrete filaments and threadlike chips) - 20-30 about. %. The above strength and a coefficient of elasticity of filaments, the above strength and ruggedness of a composite material. Properties of a die define strength of a composition at shears and squeezing and resistance to a fatigue crack.
By the form упрочнителя composite materials classify on Fiberglass, карбоволокниты with carbon filaments, бороволокниты and органоволокниты.
In stratified materials of a filament, a fiber, the ribbons soaked connecting, are laid down in parallel each other in a laying down plain. Flat stratums prepare in plates. Properties turn out non-isotropic. For material operation in an article it is important to consider a direction of operating loads. It is possible to create materials both with isotropic, and with non-isotropic properties. It is possible to lay down filaments under different edges, varying properties of composite materials. On an order of laying down of stratums on width of a bundle depend изгибные and torsional ruggedness of a material.
Laying down Uprochniteli from three, four and more fibers is applied. The structure from three orthogonally related fibers has the greatest application. Uprochniteli can settle down in axial, radial and environing directions.
Three-dimensional materials can be any width in the form of blocks, barrels. Volume fabrics augment strength by a tear and resistance to shear in comparison with the stratified. The system is under construction of four fibers by breaking-up Uprochniteli on cube diagonals. The structure from four fibers is equilibrium, has heightened ruggedness at shear in the principal plains. However creation of the four-directed materials is more difficult, than three-directed.
2. Classification of composite materials
2.1 Filamentary composite materials
Composite materials with a filamentary filling agent (Uprochniteli) on the gear of reinforcing operation divide on discrete in which ratio filaments by the diameter l/d »10 are long? 10 і, and with a continuous filament, in which l/d»?. Discrete filaments settle down in a die chaotically. Diameter of filaments from fractions to hundreds micrometers. The more a ratio are long to diameter of a filament, the above hardening degree.
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