what is a composite

8/6/2019 What is a Composite

http://slidepdf.com/reader/full/what-is-a-composite 1/5

What is a composite?

A composite is a material which is made up of

two or more distinct (i.e. macroscopic, not

microscopic) materials. A familiar composite isconcrete, which is basically made up of sand

and cement. Many common materials could beclassed as composites, but this website is

concerned with fibre reinforced polymercomposites.

Polymer composites are plastics within whichthere are embedded fibres or particles. The

plastic is known as the matrix, and the fibresor particles, dispersed within it, are known as

the reinforcement.

The reinforcement is usually stiffer than the

matrix, thus stiffening the composite material. This stiffer reinforcement will usually

be laid in a particular direction, within the matrix, so that the resulting material willhave different properties in different directions. This characteristic is usually

exploited to optimise the design.

Polymer matrix composites (PMCs) are materials that use a polymer based resin as amatrix material with some form of fibres embedded in the matrix, as a

reinforcement. Both thermosetting and thermoplastic polymers can be used for thematrix material. Common polymer composite thermosetting matrix materials include

polyester, vinyl ester and epoxy. Polymer composite thermoplastic matrix materialsinclude PEEK, PEI and PPS. Reinforcements include glass, carbonand aramid fibres.

Why use polymer composites?

There can be many secondary reasons why polymer composites may be chosen for

the manufacture of particular articles or components, but the primary reason isbecause of weight saving for their relative stiffness and strength. As an example we

can compare a carbon fibre reinforced composite with its steel counterpart. Thecarbon fibre composite can be five times stronger than 1020 grade steel while having

only one fifth the weight. Aluminium (6061 grade) is much nearer in weight tocarbon fibre composite (though still somewhat heavier), but the composite can have

twice the modulus and up to seven times the strength.

When should polymer composites be used?

http://www.netcomposites.com/vircon/3_1.asp


http://www.netcomposites.com/vircon/3_1_5_1.asp

http://www.netcomposites.com/vircon/3_2_12.asp




















Polymeric composites are one class of engineering material. As with all otherengineering materials, they have particular strengths and particular weaknesses. The

matrix protects the strong stiff fibres and together the composite material improveson the properties of either the matrix material or the fibres alone. A major driving

force behind the development of composites has been to produce materials withimproved specific mechanical properties over existing materials. Specific stiffness can

be defined as the stiffness of a material divided by the density of material andspecific strength can be defined as the strength of a material divided by the densityof the material. It is these good specific properties of composites that allow the

design of high performance structural components. Polymer composite material

structures can also be engineered so that the directionality of the reinforcementmaterial is arranged so as to match the loading on a given component or structure.

In addition, polymer composites are useful in applications where the environmentwould be detrimental to other materials. A wide selection of resins and coatings are

available to match appropriate environmental conditions. Cost is ever present in theengineering equation and it is the balance of cost and performance that determine

whether or not to use polymer composites over an alternative structural materialoption

Can polymer composites directly replace metals?

Many metal articles or components can instead be made from composites, but thereare important differences which mean that direct substitution should be made with

care.

Most engineering materials are essentially isotropic. That is, they have the sameproperties such as strength and modulus, in any direction. There may be 'grain' in

some metals due to the manufacturing process, but it is only in critical applications

that this matters. Most machining or casting processes do not have to takedirectional differences into account.

Most composites will have very different properties in different directions. This is

because, although the matrix material is isotropic, the reinforcement is not. Carbonfibres may be up to 100 times stronger under tension than they are in shear, and the

stiffness may differ in the two directions by similar ratios. The properties of thecomposite will reflect the properties of the reinforcement, so that it can have greatly

different properties in different directions. This is exploited in design asmanufactured articles rarely require to be equally strong in all directions, and

composites can achieve this by particular arrangements of the reinforcement.

However, a different design procedure is required for composites compared to that

required for metals.

.

What type of polymer composites are available?



















Polymer composites can be classifiedaccording to the type of MATRIX material, and

the type of REINFORCEMENT material.

Because the size of the reinforcementparticles, or the type and length of the fibres

can be varied, and because the directions inwhich they can be placed within the matrixcan be varied, a very wide variety of

properties can be achieved. Where necessarythe composite can have different properties in

different directions.

When we include the possibility of changing

the matrix material, it can be seen thatpolymer composites form a vast family of

engineering materials.

Click here for matrix optionsClick here for reinforcement options

What are the main factors determining the costs?

There are four factors determining the direct costs of producing articles from

reinforced polymer composites. These are:

• Material costs• Tooling costs

• Processing costs

• Finishing costs

Additionally, there may be a number of indirect costs, such as quality control, health

and safety considerations, etc. which need to be taken into account but are not dealtwith here. Also, there is an increasing emphasis on environmental factors including

maintenance , recycling, and disposal, which, over the lifetime of a component, canbe important. For many components, the benefits from the use of reinforced polymer

composites can become very significant when whole-life costs, rather than justfabrication costs, are included.

What applications are currently fabricated from composites?































Many products in a variety of industries are fabricated from composites, from fighteraircraft to bath tubs. This section gives more examples in different industries

including:

Boating

Automotive and rail

General Engineering

Aerospace

Sporting goods

Civil Engineering

Domestic

Medical

Automotive & rail

Links to other sections Item Typical Fibre Typical Resin Manufacturing


















Battery trays Glass PP Flow/compressionmoulding

Body panels SMC Compression moulding Bumper fascia Carbon/glass Polyester/rubber Compression moulding Drive shafts Carbon/ E-glass VE FW Radiator grills Glass PBT RIM Instrument panes Glass PP Flow/compression

moulding Leaf springs Glass VE/Epoxy/PE FW, Auto Engine

components Glass PP / Nylon IM Fuel lines Glass PP / Nylon Extruded Rail car bodies E-glass fabric VE/PW

what is a composite

Documents