Composite material

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The composite material (also called the composition material or abbreviated to the composite, which is the common name) is material made up of two or more constituents of the material by its nature physical or chemical differences that significantly, if combined, produce materials with different characteristics of each component. The individual components remain separate and distinct in the finished structure, distinguishing composites from mixtures and solid solutions.

New materials may be preferred for many reasons: common examples include stronger, lighter, or cheaper materials when compared to traditional materials.

Recently, researchers have also started actively incorporating sensing, actuation, computation and communication into composites, known as Robotic Materials.

Custom designed composite materials include:

• Reinforced concrete and bricks
• Composite wood like plywood
• Reinforced plastic, such as fiber-reinforced polymer or fiberglass
• Ceramic matrix compositions (ceramic matrix and composite metal)
• Metal matrix compositions
• and other advanced composite material

Composite materials are commonly used for buildings, bridges, and structures such as boat hulls, pool panels, racecars, shower kiosks, bathtubs, storage tanks, imitation granites and marble sinks and kitchen counters.

The most advanced examples do routinely in spaceships and planes in demanding environments.

Video Composite material

Histori

The earliest man-made composite materials are straw and mud combined to form bricks for building construction. The making of ancient bricks is documented by Egyptian tomb paintings.

Pial and grinding are one of the oldest man-made composite materials, in over 6000 years. Concrete is also a composite material, and is used more than any other manmade material in the world. In 2006, about 7.5 billion cubic meters of concrete was made every year - more than one cubic meter for every person on Earth.

• Wood crops, both genuine wood from trees and plants such as palm and bamboo, produce natural composites that are used prehistoric by humans and are still widely used in construction and scaffolding.
• 3400 BC plywood by Ancient Mesopotamia; sticking wood at different angles provides better properties than natural wood.
• Linen linings of linen or papyrus soaked in plaster cast from Egyptian First Period c. 2181-2055 BC and used for death mask.
Mud Bricks, or Mud Walls, (using mud (clay) with straw or gravel as a binder) have been used for thousands of years.
• Concrete is described by Vitruvius, writing about 25 BC in his book The Ten Books on Architecture , the right type of aggregate for the preparation of lime mortar. For structural mortar he recommends pozzolana, which is a volcanic sand of a grayish-brownish grayish-looking Pozzuoli near Naples and a reddish brown in Rome. Vitruvius set a ratio of 1 part lime to 3 parts of pozzolana for cement used in buildings and a ratio of 1: 2 lime for Puteolanus pulve for underwater work, essentially the same ratio mixed today for concrete used in the ocean. Natural cement stones, once burned, produce cement used in concrete from post-Roman times into the 20th century, with some properties superior to Portland cement being produced.
• Papier-mÃÆ' Â ¢ chÃÆ'Ã… ©, a combination of paper and glue, has been used for hundreds of years.
• The first artificial fiber-reinforced plastic is a bakelite dating from 1907, although natural polymers such as lac is old.
• One of the most common and familiar composites is fiberglass, in which small glass fibers are embedded in polymeric materials (usually epoxy or polyester). The glass fibers are relatively strong and stiff (but also fragile), while the polymer is ductile (but also weak and flexible). Thus the fiberglass produced is relatively stiff, strong, supple, and resilient.

Maps Composite material

Example

Composite materials

Concrete is the most common artificial composite material of all and usually consists of loose rock (aggregate) held with a cement matrix. Concrete is an inexpensive material, and will not compress or destroy even under a large compressive strength. However, concrete can not withstand the tensile load (that is, if stretched will quickly break). Therefore, to provide concrete the ability to withstand being withdrawn, a steel rod, which can withstand high stretching forces, is often added to the concrete to form reinforced concrete.

Fiber-reinforced polymers (FRP) s include carbon-reinforced polymers (CFRP) and glass-reinforced plastics (GRP). If classified by a matrix then there is a thermoplastic composite, short-fiber thermoplastic, long fiber thermoplastic or thermoplastic reinforced fiber length. There are many thermoset composites, including paper composite panels. Many advanced thermoset polymer matrix systems typically incorporate aramid fibers and carbon fibers in an epoxy resin matrix.

The form of polymer composite memory is a high-performance composite, formulated using fiber or fabric reinforcement and polymer resin form of memory as a matrix. Because polymeric resin forms of memory are used as matrices, these composites have the ability to be easily manipulated into various configurations when heated above their activation temperature and will show high strength and stiffness at lower temperatures. They can also be heated and reshaped repeatedly without losing their material properties. This composite is ideal for applications such as structures that are lightweight, rigid, discardable; fast manufacturing; and dynamic reinforcement.

High-strain composites are another type of high-performance composites designed to work in high deformation settings and are often used in systems that can be channeled where structural stretching is advantageous. Although high strain composites exhibit many similarities to forming memory polymers, their performance generally depends on the fiber layout as opposed to the resin content of the matrix.

Composites can also use metal fibers that strengthen other metals, such as in metal matrix composites (MMCs) or ceramic matrix composites (CMCs), which include bone (hydroxyapatite reinforced with collagen fibers), mirrors (ceramics and metals) and concrete. Ceramic matrix composites are built primarily for fracture toughness, not for strength. Another class of composite materials involves composite woven fabrics consisting of longitudinal and transverse laced yarns. Composite woven fabrics are flexible because they are in fabric form.

The organic composite matrix/ceramic aggregates include concrete asphalt, concrete polymer, mastic, hybrid roller resin, dental composite, syntactic foam and mother of pearl. Chobham Armor is a special type of composite armor used in military applications.

In addition, the thermoplastic composite material can be formulated with a special metal powder that produces a material with a density range from 2 g/cm³ to 11 g/cm³³ (equal to lead density). The most common name for this type of material is "high gravity compound" (HGC), although "lead replacement" is also used. These materials can be used instead of traditional materials such as aluminum, stainless steel, brass, bronze, copper, lead, and even tungsten in weighting, balancing (for example, modifying the center of gravity of tennis rackets), vibration dampers, and radiation shield applications. High density composites are an economical choice if certain ingredients are considered harmful and prohibited (such as lead) or when secondary operating costs (such as machining, finishing, or coating) are a factor.

The sandwich-structured composite is a special grade of composite material made by attaching two thin but rigid skins to a light but thick core. The core material is usually a low strength material, but its higher thickness provides a sandwich composite with high flexural rigidity with a low overall density.

Wood is a natural composite consisting of cellulose fibers in lignin and hemicellulose matrices. Wood engineering includes a wide range of different products such as wooden fiberboard, plywood, oriented strand board, composite plastic wood (recycled wood fiber in polyethylene matrix), Pykrete (sawdust in ice matrix), paper or textile impregnated or laminated plastic , Arborite, Formica (plastic) and Micarta. Other engineering laminated composites, such as Mallite, use the core of balsa core of seed tip ends, bonded to light alloy skin surface or GRP. It produces low-stiffness and high-duty materials.

Composite particulates have particles as fillers dispersed in matrices, which may not be metals, such as glass, epoxy. Car tires are examples of composite particulates.

Sophisticated polymer coated diamond composites (DLC) have been reported in which the coating increases surface hydrophobicity, hardness and wear resistance.

Products

The fiber-reinforced composite material has gained popularity (albeit high cost) in high-performance products that need light, yet strong enough to pick up harsh loading conditions such as aerospace components (tail, wings, fuselages, propellers), skull boats and hulls, bike framework and racing car body. Other uses include fishing rods, storage tanks, pool panels, and baseball bats. The structure of Boeing 787 and Airbus A350 including wings and fuselage is composed mostly of composites. Composite materials are also becoming more common in the field of orthopedic surgery. And that is the most common hockey stick material.

The carbon composite is a key ingredient in today's launch vehicle and a heat shield for the space shuttle re-entry phase. It is widely used in solar panel substrates, antenna reflectors and spaceships. It is also used in charge adapters, inter-stage structures and heat shields from launch vehicles. Furthermore, aircraft and racing disc brake systems use carbon/carbon materials, and composite materials with carbon fiber and silicon carbide matrices have been introduced in luxury vehicles and sports cars.

In 2006, a fiber reinforced composite pool panel was introduced for indoor, residential and commercial pools, as a non-corrosive alternative to galvanized steel.

In 2007, an all-composite military Humvee was introduced by TPI Composites Inc. and Armour Holdings Inc., the first combined military vehicle. By using lighter composite vehicles, allowing higher payloads. In 2008, carbon fiber and DuPont Kevlar (five times stronger than steel) combined with enhanced thermoset resins to make military transit cases by ECS Composites created 30 percent of lighter cases with high strength.

Pipes and fittings for various purposes such as drinking water transport, fire fighting, irrigation, seawater, wastewater, chemical and industrial waste, and waste are now produced in glass-reinforced plastics.

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Overview

The composite consists of individual materials called composers. There are two main categories of constituent materials: matrix (binder) and reinforcement . At least one part of each type is required. Matrix materials surround and support reinforcement materials by maintaining their relative positions. Reinforcements provide their specific mechanical and physical properties to improve the matrix properties. Synergism produces unavailable material properties of individual constituent materials, while various matrices and reinforcement materials enable the product or structure designer to choose the optimal combination.

Engineered composite materials must be formed to form. The matrix material can be introduced to the reinforcement before or after the reinforcing material is placed into the mold cavity or onto the mold surface. Matrix material experiences a melting event, after which the shape of the part is basically arranged. Depending on the nature of the matrix material, this melting event may occur in various ways such as chemical polymerization for the thermoset polymer matrix, or freezing of the melting state for thermoplastic polymer matrix composites.

Various printing methods can be used in accordance with the final goods design requirements. The main factors affecting the methodology are the properties of the matrix and the selected reinforcing material. Another important factor is the amount of gross material to be produced. Large quantities can be used to justify high capital expenditures for rapid and automated manufacturing technology. Small production quantities are accommodated with lower capital expenditures but labor and tool costs are higher at a slower rate.

Many commercially produced composites use a polymeric matrix material often called a resin solution. There are many different polymers available depending on the initial raw material. There are several major categories, each with many variations. The most commonly known as polyester, vinyl ester, epoxy, phenolic, polymide, polyamide, polypropylene, PEEK, and others. The reinforcing materials are often fiber but also usually mineral soils. The various methods described below have been developed to reduce the resin content of the final product, or increased fiber content. As a rule of thumb, produce a product containing 60% resin and 40% fiber, while a vacuum infusion provides an end product with 40% resin and 60% content fiber. The power of the product depends heavily on this ratio.

Martin Hubbe and Lucian A Lucia consider wood as a natural composite of cellulosic fibers in a lignin matrix.

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Constituent

Matrix

Organic

Polymers are common matrix (mainly used for fiber-reinforced plastics). Road surfaces are often made of asphalt concrete using asphalt as a matrix. Mud (clad and daub) has been widely used. Typically, the most common polymer-based composite materials, including fiberglass, carbon fiber, and Kevlar, include at least two parts, substrate and resin.

Polyester resins tend to have yellowish tones, and are suitable for most backyard projects. The disadvantage is that UV is sensitive and may tend to decrease over time, and thus is generally also coated to help preserve it. These are often used in the manufacture of surfboards and for marine applications. The hardener is peroxide, often MEKP (methyl ethyl ketone peroxide). When the peroxide is mixed with resin, the peroxide decomposes to produce free radicals, which initiate the curing reaction. Hardener on this system is generally called a catalyst, but since they do not reappear unchanged at the end of the reaction, they are incompatible with the strictest chemical definitions of the catalyst.

Vinyl ester resins tend to have a purplish color to bluish to greenish. This resin has a lower viscosity than polyester resin and is more transparent. These resins are often billed as fuel resistant, but will melt in contact with gasoline. It tends to be more resistant over time for the degradation of polyester resins and more flexibility. It uses the same hardener with polyester resin (with the same mix ratio) and costs about the same.

Epoxy resins are almost transparent when cured. In the aerospace industry, epoxy is used as a structural matrix material or as a structural glue.

The shape of polymer memory resin (SMP) has visual characteristics that vary depending on the formulation. This resin may be epoxy-based, which can be used for the repair of car bodies and outdoor equipment; based ester-catalyst, used in aerospace applications; and acrylic-based, which can be used in very cold temperature applications, such as for sensors that indicate whether defective items have been warmed above a certain maximum temperature. This resin is unique because its shape can be changed repeatedly by heating above its glass transition temperature (T _g ). When heated, they become flexible and elastic, allowing easy configuration. Once cooled, they will retain their new shape. The resin will return to its original shape when heated on top of T _g them. The advantage of polymer form memory resins is that they can be shaped and reshaped repeatedly without losing their material properties. This resin can be used in the manufacture of composite form memory.

Traditional materials such as glue, sludge have traditionally been used as matrices for papier-mÃÆ' Â ¢ chÃÆ' Â © and adobe.

Inorganic

Cement (concrete), metal, ceramics, and sometimes glasses are used. Unusual matrices such as ice are sometimes proposed as pykecrete.

Reinforcements

Fiber

Reinforcement usually adds stiffness and greatly inhibits crack propagation. Thin fibers can have very high strength, and provided they are mechanically attached well to their matrices can greatly improve the overall nature of the composite.

The fiber-reinforced composite material can be divided into two main categories commonly referred to as short-fiber reinforced materials and sustainable fiber reinforced materials. Continuously reinforced material will often form a layered structure or laminate. The woven and continuous fiber style is usually available in various shapes, which are pre-impregnated with a given matrix (resin), dried, uni-directional ribbons of various widths, plain weave, satin harness, braided, and sewn.

Short and long fibers are commonly used in compression molding and sheet printing operations. These come in the form of flakes, chips, and random pairs (which can also be made from continuous fibers that are placed randomly until the desired thickness of the laminate is achieved).

Common fibers used for reinforcement include glass fibers, carbon fibers, cellulose (wood fibers/paper and straw) and high strength polymers eg aramid. Silicon carbide fibers are used for some high temperature applications.

Particles

Strengthening of particles adds a similar effect to precipitation precipitation in metals and ceramics. Large particles inhibit the movement of dislocations and crack propagation as well as contribute to Young's composite modulus. In general, the effect of particle reinforcement on Young's Modulus lies between predicted values ​​by

${\ displaystyle E_ {c} = {\ frac {E _ {\ alpha} E _ {\ beta}} {(V_ {\ alpha} E_ {\ beta} V_ { \ beta} E_ {\ alpha})}}}  ÂÂ$

as a lower bound and

${\ displaystyle E_ {c} = V_ {\ alpha} E_ {\ alpha} V_ {\ beta} E_ {\ beta}}  ÂÂ$

as the upper limit.

It can therefore be expressed as a linear combination of the contributions of the matrix and some of the weighted contributions of the particles.

${\ displaystyle E_ {c} = V_ {m} E_ {m} K_ {c} V_ {p} E_ {p}}  ÂÂ$

Where K _c is a constant obtained experimentally between 0 and 1. This range of values ​​for K _c reflects that the particle-reinforced composite is not characterized by isostrain conditions.

Similarly, the tensile strength can be modeled in a similar construction equation where K _s is the same bound constant not always from the same value of K _c

${\ displaystyle (TS) _ {c} = V_ {m} (TS) _ {m} K_ {s} V_ {p} (TS) _ {p} }  ÂÂ$

The true values ​​of K _c and K _s vary by factors including particle shape, particle distribution, and particle/matrix interfaces. Knowing these parameters, mechanical properties can be modeled based on the effects of grain boundary reinforcement, strengthening dislocations, and Orowan reinforcement.

The most commonly reinforced particles are concrete, which is a mixture of gravel and sand which is usually reinforced by the addition of small stones or sand. Metals are often reinforced with ceramics to increase strength with the cost of toughness. Finally polymers and rubbers are often reinforced with carbon black, commonly used on automobile tires.

Cores

Many composite layup designs also include curing or pascuring of prepreg with various other media, such as honeycomb or foam. This is called sandwich structure. This is a more common layup for the manufacture of radom, door, cowling, or non-structural parts.

Open and closed structured foams such as polyvinylchloride, polyurethane, polyethylene or polystyrene foam, balsa wood, syntactic foam, and honeycomb are commonly used core materials. Open metal foam and closed cells can also be used as core materials. More recently, 3D graphene structures (also called graphene foam) are also used as core structures. Recent reviews by Khurram and Xu et al., Have provided a summary of state-of-the-art techniques for fabrication of 3D graphene structures, and examples of the use of such foam structures as the core for them. respectively polymer composites.

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Fabrication method

Fabrication of composite materials is done with a variety of techniques, including:

• Advanced fiber placement (Automatic fiber placement)
• Adjusted fiber placement
• fiberglass spray lay-out process
• Filament rolls
• The lanxide process
• Tufting
• Z-pinning

Composite fabrication usually involves wetting, mixing or saturating the reinforcement with a matrix, and then causing the matrix to bind together (with heat or chemical reactions) into a rigid structure. This operation is usually done in an open or closed form mold, but the order and ways of introducing the material vary.

Print overview

In the mold, the reinforcing and matrix materials are combined, compacted, and healed (processed) to undergo a fusible event. After the smelting event, the shape of the section is essentially arranged, although it may change shape under certain process conditions. For the thermoset polymer matrix material, the melting event is a preservation reaction initiated by the application of additional heat or chemical reactivity such as organic peroxides. For the thermoplastic polymer matrix material, the melting event is a solidification of the melting state. For metal matrix materials such as titanium foil, the melting event is melting at high pressure and near melting point temperature.

For many printing methods, it would be easier to refer to a single piece of mold as a "lower" mold and other mold parts as a "top" mold. The bottom and top refers to the various faces of the panel being formed, not the configuration of the mold in space. In this convention, there is always a lower print, and sometimes a top mold. Part construction begins by applying the material to a lower mold. Bottom prints and upper prints are more general descriptions of more general and specific terms such as male, female side, side-side, b-sides, tool sides, bowls, hats, mandrels, etc. Sustainable manufacturing uses different nomenclature.

Vacuum bag molding uses flexible film to attach parts and seal it from the outside air. The material of the vacuum bag is available in the form of a tube or piece of material. The vacuum is then drawn on the vacuum bag and atmospheric pressure presses the part during healing. When a tubular bag is used, all parts can be flanked in a bag. When using a bagging sheet material, the ends of the vacuum bag are sealed on the edges of the mold surface to cover the section with airtight prints. When bagged in this way, the lower mold is a rigid structure and the upper surface is formed by a flexible membrane vacuum bag. The flexible membrane can be a reusable silicone material or an extruded polymer film. After sealing the part inside the vacuum bag, the vacuum is drawn on the part (and held) during healing. This process can be done at ambient or high temperature with ambient atmospheric pressure working on the vacuum bag. Vacuum pumps are usually used to draw a vacuum. The economical method for vacuum drawing is by vacuum venturi and air compressor.

Vacuum bags are bags made of strong rubber-coated fabrics or polymer films used to press parts during healers or hardening. In some applications the bag wraps the entire material, or in other applications the mold is used to form a single face laminate with a pouch that becomes a single layer to seal onto the outer edge of the mold. When using a tubular bag, the end of the bag is sealed and air is pulled out of the bag through the nipple using a vacuum pump. As a result, uniform pressure approaching one atmosphere is applied to the surface of the object inside the bag, holding the parts together while the adhesive heals. The entire bag can be placed in a temperature controlled oven, an oil bath or a water bath and heated gently to speed up the curing process.

Vacuum packing is widely used in the composite industry as well. Carbon fiber and fiberglass fabrics, together with resins and epoxies are common materials laminated together with vacuum bag operation.

Woodworking Applications

In commercial woodworking facilities, vacuum pockets are used for curved and irregularly shaped workpieces.

Usually, a polyurethane or vinyl material is used to make a bag. A tubular tube opened at both ends. Pieces, or grimed pieces are inserted into the bag and sealed ends. One method of sealing the open end of the bag is to place a clamp on each end of the bag. A plastic rod is placed at the end of the bag, the bag is then folded over the stem. A plastic sleeve with openings in it, then tied to the stem. This procedure forms a seal at both ends of the bag, when the vacuum is ready to be taken.

"Plates" are sometimes used in bags for pieces that are attached to lie. The plate has a series of small slits cut into it, to allow air underneath to be evacuated. The plates should have rounded edges and corners to prevent the vacuum tearing the bag.

When the curved portion should be glued in a vacuum bag, it is important that the embedded piece be placed on a sturdy shape, or have an air bladder placed under the shape. This air bag has access to "free air" outside the bag. This is used to create the same pressure under the form, preventing it from being destroyed.

Print pressure bag

This process is related to the printing of a vacuum bag in exactly the same way as it sounds. Dense female molds are used along with flexible male prints. Reinforcement is placed inside a female mold with enough resin to allow the cloth to stick in place (wet lay up). A measured amount of resin is then freely brushed indiscriminately into the mold and the mold is then clamped onto a machine containing the male flexible mold. Flexible male membranes are then pumped with hot press or perhaps steam. Female molds can also be heated. The excess resin is forced out along with the trapped air. This process is widely used in the production of composite helmets due to lower unskilled labor costs. The cycle time for a helmet bag printing machine varies from 20 to 45 minutes, but the finished shell does not need to be dried again if the mold is heated.

Autoclave molding

A process uses a two-sided mold set that forms both panels of the panel. On the underside is a rigid mold and on the upper side is a flexible membrane made of silicon or an extruded polymer film such as nylon. The reinforcement material can be placed manually or robotically. They include a continuous form of fiber formed into a textile construction. Most often, they are pre-impregnated with resin in the form of prepreg or ribbon. In some cases, the resin film is placed on a lower mold and a dry amplifier is placed on top. The top mold is installed and the vacuum is applied to the mold cavity. The assembly is placed into the autoclave. This process is generally carried out at high pressure and high temperature. The use of high pressure facilitates high volume fiber fractions and low void content for maximum structural efficiency.

Resin transfer printing (RTM)

RTM is a process that uses rigid double-sided molds that form both panels. Molds are usually made of aluminum or steel, but composite molds are sometimes used. Both sides are suitable for producing mold cavities. A distinguishing characteristic of resin molding transfers is that the reinforcing materials are placed into this cavity and the molding device is closed before the introduction of the matrix material. The resin transfer mold includes many different varieties in mechanics on how the resin is introduced to the amplifier in the mold cavity. This variation includes everything from the RTM method used in the manufacture of autoclave composites for high-tech aerospace components for vacuum infusions (for resin infus see also shipbuilding) for vacuum assisted resin transfer molding (VARTM). This process can be done at ambient temperature or high temperature.

Other fabrication methods

Other types of fabrication include press molding, transfer molding, pultrusion molding, filament winding, casting, centrifugal casting, continuous casting and slip forming. There are also forming capabilities including CNC winding filaments, vacuum infusions, wet lay-ups, compression molding, and thermoplastic printing, to name a few. The use of preserving ovens and paint booths is also required for some projects.

Finishing method

The termination of composite parts is also important in the final design. Much of this final result will include layers of rain erosion or polyurethane coatings.

Tools

Prints and insertion molds are referred to as "tools." Molds/tools can be constructed from various materials. Tool materials include invar, steel, aluminum, reinforced silicone rubber, nickel, and carbon fiber. The choice of tool material is usually based on, but not limited to, the coefficient of thermal expansion, the number of expected cycles, the end-item tolerance, the desired surface conditions or required, the healing method, the glass transition temperature of the formed material, the molding method, the matrix, the cost and various other considerations.

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Physical properties

The physical properties of composite materials are generally not isotropic (regardless of the direction of forces applied) in nature, but their properties are usually anisotropic (differing depending on the direction of force or load applied). For example, the rigidity of composite panels often depends on the orientation of the applied style and/or moment. The composite strength is limited by two loading conditions as shown in the plot to the right. If both fiber and matrix are parallel to the loading direction, the deformations of both phases will be the same (assuming no delamination on the matrix-fiber interface). This isostrain condition provides an upper limit for composite strength, and is determined by mixed rules:

${\ displaystyle E_ {C} = \ jumlah _ {i = 1} V_ {i} E_ {i}}  ÂÂ$

where E _C is the effective Young composite modulus, and V _i is the volume fraction and Young modulus, respectively, of the composite phase.

For example, composite materials consist of? and? the phase as shown in the picture to the right under the isostrain, Young modulus is as follows: where V _? and V _? is the volume fraction of each phase.

The lower limit is determined by isostress conditions, where fibers and matrices are oriented perpendicular to the loading direction:

${\ displaystyle {\ frac {1} {E_ {C}}} = \ jumlah _ {i = 1} {\ frac {V_ {i}} {E_ {i }}}}  ÂÂ$

Following the example above, if any are made of composite material? and? phase under the isostress condition as shown in the picture on the right, Young modulus's composition will be: The isostrain condition implies that under applied load, both phases undergo the same strain but will feel different pressure. Relatively, under isostress conditions the two phases will feel the same pressure but the strain will differ between each phase. Although the composite rigidity is maximized when the fibers are parallel to the loading direction, so the possibility of tensile fiber fracture, assuming a tensile strength exceeds that of the matrix. When the fiber has multiple angles of misorientation ?, some fracture modes are possible. For small values? the stress required to initiate the fracture increases with the (cos?) ^-2 factor due to the increased cross-sectional area ( A cos?) of the fiber and the reduced force ( F/ cos?) Experienced by the fiber, leading to a composite tensile strength ? _parallel / cos ² ? where ? _parallel is the composite tensile strength with parallel fibers parallel to the applied force.

Intermediate misorientation angle? causing shear failure of matrix. Again the cross-sectional area is modified but because the shear stress is now the driving force for failure of the matrix area parallel to the attractive fibers, increasing by a factor of 1/sin ?. Similarly, the force parallel to this area decreases ( F/ cos?) Which leads to total tensile strength ? _{my sin} /? cos? where ? _my is the shear force of the matrix.

Finally, for the big values? (near?/2) the transversal matrix failure is most likely to occur, since fiber no longer carries most of the load. However, the tensile strength will be greater than for pure perpendicular orientation, since the force perpendicular to the fiber will decrease by a factor of 1/sin? and its extent reduced by a factor of 1/sin? generate composite tensile strength ? _perp / sin ² ? where ? _perp is the tensile strength of the composite with the fiber parallel to perpendicular to the applied force.

Most commercial composites are formed with random dispersion and reinforced fiber orientation, in this case Young Composite modulus will fall between the isostrain and the isostress boundary. However, in applications where the strength-to-weight ratio is engineered to the highest possible (as in the aerospace industry), fiber alignment can be strictly controlled.

Panel rigidity also depends on the panel design. For example, fiber and matrix reinforcers are used, panel manufacturing methods, thermosets versus thermoplastics, and woven types.

Unlike composites, isotropic materials (eg, aluminum or steel), in the form of standard forgings, usually have the same rigidity regardless of the orientation of the applied force and/or moment. The relationship between force/moment and strain/indentation for isotropic material can be explained by the following material properties: Young Modulus, Shear Modulus and Poisson Ratio, in relatively simple mathematical relationships. For anisotropic materials, mathematics from second order tensors and up to 21 material properties constants are required. For the special case of orthogonal isotropy, there are three different material property constants for each Young Modulus, Shear Modulus and Poisson ratios - a total of 9 constants to illustrate the relationship between force/moment and strain/indentation.

Techniques that take advantage of the anisotropic properties of materials include mortise and tenon joints (in natural composites such as wood) and Pi Joints in synthetic composites.

Failure

Shock, impact, or recurrent cyclic tension can cause separate laminations at the interface between two layers, a condition known as delamination. Individual fibers can be separated from a matrix eg. fiber pull-out.

Composites may fail on microscopic or macroscopic scales. Compression failures can occur either on a macro scale or on individual individual reinforcing fibers in a compression buckling. Voltage failure may be a part of the net part failure or composite degradation on a microscopic scale in which one or more of the layers in the composite fails in the matrix voltage or bond failure between the matrix and the fiber.

Some composites are fragile and have little backup power beyond the initial onset of failure while others may have large deformations and have the capacity to absorb backup energy through the initial damage. Available variations of fiber and matrix and mixtures that can be made with the mixture leave a wide variety of properties that can be designed into composite structures. The most notable failure of the brittle ceramic matrix composite occurs when composite carbon-carbon tiles on the leading edge of the Space Shuttle Columbia wing are cracked when impacted during take-off. This led to the destruction of the vehicle when it reentered Earth's atmosphere on February 1, 2003.

Compared to metals, composites have relatively poor bearing strength.

Test

To help predict and prevent failure, composites are tested before and after construction. Pre-construction testing can use finite element analysis (FEA) for curved surface layer analysis and predict wrinkling, crimping and composite dimpling. The materials can be tested during manufacture and after construction through some nondestructive methods including ultrasonic, thermography, shearography and X-ray radiography, and laser bonding checks for NDT from the integrity of relative bond strength in local areas.

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See also

• Aluminum composite panel
• The American Composite Manufacturers Association
• Chemical vapor infiltration
• Composite (disambiguation)
• Composite laminate
• Epoxy Granite
• Hybrid material
• Nanocomposite
• Mixed rule
• Composite scale, American aerospace company founded by Burt Rutan
• Void (composite)

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References

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Further reading

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External links

• CompositesPress | Social Networking Composite
• Composite Design and HUB Manufacturing
• Distance learning courses in polymers and composites
• High Density Composite Replace Lead
• Composite Strength
• Composite Structure of Minardi F1 Car Composite
• OptiDAT composite material database
• The test originally developed to test the metal has been adapted by the industry to test the composite
• The world's leading center for advanced composites

Source of the article : Wikipedia