CompositesA composite is a material with two or more distinct constituents.These separate constituents act together to give the necessary strength and stiffness to the composite material. The most common example of a composite material today is that of fibre reinforcement of a resin matrix but the term can also be applied to other materials such as metal-skinned honeycomb panels. The property that these materials have in common is that they are light, stiff and strong and, what’s more, they can be extremely tough.

Reinforced concrete is another example of a composite material that is invaluable in engineering. The steel and concrete retain their individual identities in the finished structure.

Unit 1 Composites

Composite materialsComposite materials are quite different from any of the materials that we have met so far. As their name suggests, composite materials are combinations of materials that, however, unlike their individual constituents, retain their separate identities and do not dissolve ormerge together. In structural applications composite materials have the following characteristics:1. They generally consist of two or more physically distinct and mechanically separable materials.2. They are made by mixing the separate materials in such a way as to achieve controlled and uniform dispersion of the constituents.3. The mechanical properties of the composite material are superior to (and in many cases quite different from) the properties of the constituent materials.A good example of a composite material is glass-reinforced plastic (GRP). This material combines glass fibres with epoxy resin. The latter material is relatively weak and brittle and, although the glass fibres are strong and stiff, they can only be effectively loaded in tension as single fibres. However, when combined into a composite material, the resin and fibre provide us with a strong, stiff material with excellent toughness characteristics.

The following materials are commonly used as fibres:• alumina• boron• carbon• glass• polyethylene• polyamide.

The following materials are used as matrix materials:• alumina• aluminium• epoxy• polyester• polypropylene.

The fibres may be arranged within the matrix material in various ways depending on the properties required and the intended application (see Figure 1.3). Note that, whenever the fibres are aligned in a specific direction, the properties of the material also become direction. Conversely, if the fibres are arranged in random orientation, the resulting material will have the same properties in all directions. This is an important point because we may sometimes require that a component has maximum strength in a particular

Unit 1 Composites

The force of Earth's gravity on (= the weight of) a human being with a mass of 70 kg is approximately 686 N

1 N is the force of Earth's gravity on a mass of about 102 g = (1⁄9.81 kg)

Common multiple units of the pascal are the hectopascal (1 hPa ≡ 100 Pa) which is equal to 1 mbar kilopascal (1 kPa ≡ 1000 Pa)megapascal (1 MPa ≡ 1,000,000 Pa)gigapascal (1 GPa ≡ 1,000,000,000 Pa)

The pascal (symbol: Pa) is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, defined as one newton per square metre.

Fibre alignment in composite materials

Construction of fibre mats

The force of Earth's gravity on (= the weight of) a human being with a mass of 70 kg is approximately 686 N

1 N is the force of Earth's gravity on a mass of about 102 g = (1⁄9.81 kg)

Common multiple units of the pascal are the hectopascal (1 hPa ≡ 100 Pa) which is equal to 1 mbar kilopascal (1 kPa ≡ 1000 Pa)megapascal (1 MPa ≡ 1,000,000 Pa)gigapascal (1 GPa ≡ 1,000,000,000 Pa)

The pascal (symbol: Pa) is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, defined as one newton per square metre.