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Composite material

Composite material

A cloth of woven carbon fiber filaments, a common element in composite materials Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure.


Plywood is a common composite material that many people encounter in their everyday lives The most primitive composite materials were straw and mud combined to form bricks for building construction; the Biblical book of Exodus speaks of the Israelites being oppressed by Pharaoh, by being forced to make bricks without straw being provided. The ancient


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technology. Small production quantities are accommodated with lower capital expenditures but higher labor and tooling costs at a correspondingly slower rate. Most commercially produced composites use a polymer matrix material often called a resin solution. There are many different polymers available depending upon the starting raw ingredients. There are several broad categories, each with numerous variations. The most common are known as polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, PEEK, and others. The reinforcement materials are often fibers but also commonly ground minerals. The various methods described below have been developed to reduce the resin content of the final product, or the fibre content is increased. As a rule of thumb, lay up results in a product containing 60% resin and 40% fibre, whereas vacuum infusion gives a final product with 40% resin and 60% fibre content. The strength of the product is greatly dependent on this ratio.

Composite material
The molded product is often referred to as a panel. For certain geometries and material combinations, it can be referred to as a casting. For certain continuous processes, it can be referred to as a profile. Applied with a pressure roller, a spray device or manually. This process is generally done at ambient temperature and atmospheric pressure. Two variations of open moulding are Hand Layup and Spray-up.

Vacuum bag moulding
A process using a two-sided mould set that shapes both surfaces of the panel. On the lower side is a rigid mould and on the upper side is a flexible membrane or vacuum bag. The flexible membrane can be a reusable silicone material or an extruded polymer film. Then, vacuum is applied to the mould cavity. This process can be performed at either ambient or elevated temperature with ambient atmospheric pressure acting upon the vacuum bag. Most economical way is using a venturi vacuum and air compressor or a vacuum pump.

Moulding methods

Pressure bag moulding
This process is related to vacuum bag moulding in exactly the same way as it sounds. A solid female mould is used along with a flexible male mould. The reinforcement is place inside the female mould with just enough resin to allow the fabric to stick in place. A measured amount of resin is then liberally brushed indiscriminately into the mould and the mould is then clamped to a machine that contains the male flexible mould. The flexible male membrane is then inflated with heated compressed air or possibly steam. The female mould can also be heated. Excess resin is forced out along with trapped air. This process is extensively used in the production of composite helmets due to the lower cost of unskilled labor. Cycle times for a helmet bag moulding machine vary from 20 to 45 minutes, but the finished shells require no further curing if the moulds are heated. .

Autoclave moulding


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Composite material

The physical properties of composite materials are generally not isotropic (independent of direction of applied force) in nature, but rather are typically orthotropic (different depending on the direction of the applied force or load). For instance, the stiffness of a composite panel will often depend upon the orientation of the applied forces and/or moments. Panel stiffness is also dependent on the design of the panel. For instance, the fiber reinforcement and matrix used, the method of panel build, thermoset versus thermoplastic, type of weave, and orientation of fiber axis to the primary force. In contrast, isotropic materials (for example, aluminium or steel), in standard wrought forms, typically have the same stiffness regardless of the directional orientation of the applied forces and/or moments. The relationship between forces/moments and strains/curvatures for an isotropic material can be described with the following material properties: Young’s Modulus, the Shear Modulus and the Poisson’s ratio, in relatively simple mathematical relationships. For the anisotropic material, it requires the mathematics of a second order tensor and up to 21 material property constants. For the special case of orthogonal isotropy, there are three different material property constants for each of Young’s Modulus, Shear Modulus and Poisson’s ratio--a total of 9 constants to describe the relationship between forces/moments and strains/curvatures.

Resin transfer moulding (RTM)

Other types of molding include press molding, transfer molding, pultrusion molding, filament winding, casting, centrifugal casting and continuous casting. There are also forming capabilities including CNC filament winding, vacuum infusion, wet lay-up, compression molding, and thermoplastic molding, to name a few. The use of curing ovens and paint booths is also needed for some projects.[1]

Typically, most common composite materials, including fiberglass, carbon fiber, and kevlar, include at least two parts, the substrate and the resin.



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Polyester resin, tends to have yellowish tint, and is suitable for most backyard projects. Its weaknesses are that it is UV sensitive and can tend to degrade over time, and thus generally is also coated to help preserve it. It is often used in the making of surfboards and for marine applications. Its hardener is a MEKP, and is mixed at 14 drops per oz. MEKP is composed of methyl ethyl ketone peroxide, a catalyst. When MEKP is mixed with the resin, the resulting chemical reaction causes heat to build up and cure or harden the resin. Vinylester resin, tends to have a purplish to bluish to greenish tint. This resin has lower viscosity than polyester resin, and is more transparent. This resin is often billed as being fuel resistant, but will melt in contact with gasoline. This resin tends to be more resistant over time to degradation than polyester resin, and is more flexible. It uses the same hardener as polyester resin (at the same mix ratio) and the cost is approximately the same. Epoxy resin is almost totally transparent when cured. In the aerospace industry, epoxy is used as a structural matrix material or as a structural glue.

Composite material

Categories of fiber-reinforced composite materials

To aid in predicting and preventing failures, composites are tested before and after construction. Pre-construction testing uses computer aided engineering tools such as NEi Software Nastran FEA (finite element analysis) for ply-by-ply analysis of curved surfaces and predicting wrinkling, crimping and dimpling of composites.[2] . Materials may be tested after construction through several nondestructive methods including ultrasonics, thermography, shearography and X-ray radiography[3]




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thermoplastics or long fiber-reinforced thermoplastics. There are numerous thermoset composites, but advanced systems usually incorporate aramid fibre and carbon fibre in an epoxy resin matrix. Composites can also use metal fibres reinforcing other metals, as in metal matrix composites or MMC. Magnesium is often used in MMCs because it has similar mechanical properties as epoxy. The benefit of magnesium is that it does not degrade in outer space. Ceramic matrix composites include bone (hydroxyapatite reinforced with collagen fibers), Cermet (ceramic and metal) and concrete. Ceramic matrix composites are built primarily for toughness, not for strength. Organic matrix/ceramic aggregate composites include asphalt concrete, mastic asphalt, mastic roller hybrid, dental composite, syntactic foam and mother of pearl. Chobham armour is a special composite used in military applications. Additionally, thermoplastic composite materials can be formulated with specific metal powders resulting in materials with a density range from 2 g/cm³ to 11 g/cm³ (same density as lead). These materials can be used in place of traditional materials such as aluminum, stainless steel, brass, bronze, copper, lead, and even tungsten in weighting, balancing, vibration dampening, and radiation shielding applications. High density composites are an economically viable option when certain materials are deemed hazardous and are banned (such as lead) or when secondary operations costs (such as machining, finishing, or coating) are a factor. Engineered wood includes a wide variety of different products such as plywood, oriented strand board, wood plastic composite (recycled wood fiber in polyethylene matrix), Pykrete (sawdust in ice matrix), Plastic-impregnated or laminated paper or textiles, Arborite, Formica (plastic) and Micarta. Other engineered laminate composites, such as Mallite, use a central core of end grain balsa wood, bonded to surface skins of light alloy or GRP. These generate low-weight, high rigidity materials.

Composite material
loading conditions such as aerospace components (tails, wings, fuselages, propellers), boat and scull hulls, bicycle frames and racing car bodies. Other uses include fishing rods and storage tanks. The new Boeing 787 Dreamliner structure including the wings and fuselage is composed of over 50 percent composites. Carbon composite is a key material in today’s launch vehicles and spacecraft. It is widely used in solar panel substrates, antenna reflectors and yokes of spacecraft. It is also used in payload adapters, inter-stage structures and heat shields of launch vehicles. In 2007 an all-composite military High Mobility Multi-purpose Wheeled Vehicle (HMMWV or Hummvee) was introduced by TPI Composites Inc and Armor Holdings Inc, the first all-composite military vehicle. By using composites the vehicle is lighter, allowing higher payloads. In 2008 carbon fiber and DuPont Kevlar (five times stronger than steel) were combined with enhanced thermoset resins to make military transit cases by ECS Composites creating 30-percent lighter cases with high strength. Also in 2008, an all-composite recreational vehicle RV was introduced by Pilgrim International Inc. The shell composed of CosmoLite, a thermoplastic fiber-reinforced composite and the exterior surface SpectraLite which incorporates DuPont Surlyn, an impact-resistant coating found on golf balls. In 2006, Microcosm Inc. successfully completed qualification tests on an all-composite cryogenic LOX tank. In testing done for the Scorpius Space Launch Company (SSLC), Microcosm successfully tested a 42-inch diameter all-composite liquid oxygen (LOX) tank to nearly 4 times its operating pressure of 550 psi. Testing was done at cryogenic temperatures using liquid nitrogen. The work was done as part of the technology development program for the Scorpius family of lowcost, responsive launch vehicles. Currently, Microcosm Inc. is in the process of qualifying a cryogenic tank with a MEOP (mean operating pressure) of 1500 psi and a safety factor of 2.0.[4]

Composite materials have gained popularity (despite their generally high cost) in highperformance products that need to be lightweight, yet strong enough to take harsh

See also
• Alloy • Metal matrix composite


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• Aluminium composite panel • American Composites Manufacturers Association • Cermet • Chemical vapor infiltration • Composite armour • Dental composite • Fibre • • • • • Mixture Polymer Thermoplastic Thermoset Reinforced concrete • Fiber reinforced concrete • Short Fiber Reinforced Blends

Composite material AQV2N4.pdf [4] Products, High Pressure Vessel Technology,

Further reading
• Autar K. Kaw (2005). Mechanics of Composite Materials (2nd ed.). CRC. ISBN 0-84-931343-0. • Handbook of Polymer Composites for Engineers By Leonard Hollaway Published 1994 Woodhead Publishing • Matthews, F.L. & Rawlings, R.D. (1999). Composite Materials: Engineering and Science. Boca Raton: CRC Press. ISBN 0-84-930621-3.

[1] PCT [2] Waterman, Pamela J., "The Life of Composite Materials", Desktop Engineering Magazine April 2007, [3] Matzkanin, George A.; Yolken, H. Thomas, "Techniques for the Nondestructive Evaluation of Polymer Matrix Composites", AMMTIAC Quarterly Vol. 2, No 4,

External links
• Composite material key concepts • Distance learning course in polymers and composites • Composite Sandwich Structure of Minardi F1 Car • Teaching support materials for the University of Plymouth composites degree • [1]

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