IBDP Design Technology - 4.2f Composites

Final Production / 4.2f /
Composites

Composites are an important material in an intensely competitive global market. New materials and technologies are being produced frequently for the design and rapid manufacture of high-quality composite products. Composites are replacing more traditional materials as they can be created with properties specifically designed for the intended application. Carbon fibre has played an important part in weight reduction for vehicles and aircraft.

4.2f.1 Form: fibres/sheet/particles and matrix/reinforcement

Mixes of different Fibres can be spun into thread or heated and extruded as filament. Threads or filament of different 'pure' materials can also be woven (matted) into sheet material to make fibre composites. Commonly used examples of fibre composites are carbon fiber and kevlar.

Particle reinforcement in particle composites is a less effective means of strengthening than fibre reinforcement. Particle-reinforced composites achieve gains in stiffness, but can also achieve increases in strength, toughness and wearability. A commonly used example concrete.

Laminar composites layer different materials to obtain the combined properties of the of the materials. The sheet material in the layers can in itself be composite materials again. Commonly used examples of laminar composites are shatterproof glass and plywood.

With fibre and particle composites, there are usually two types of constituent materials - matrix (or embedding) and reinforcement. The matrix provides a medium for binding and holding reinforcements together as a solid. The matrix for carbon fibre is epoxy resin, that surrounds and supports the reinforcement material: The woven carbon fibre fabric.

There are endless ways to combine matrix and reinforcement materials. And therefore many different composites have been engineered. Many industries are very protective of the particular composites they use. Many are patented.

In tungsten tooltips, hard tungsten carbide particles are located in a softer matrix

4.2f.2 | Process: weaving, moulding, pultrusion and lamination

Composites can be constructed by weaving different materials into one fabric. The thread that is woven can already be a composite in itself. Note that weaving can be done in two dimensions, but also in three. This allows the weaving of thicker fabrics. In the textiles subtopic, we learned that there are different weaving patterns as well.

Composites can also be formed by using moulds. Again the cast or moulded material can be a composite in itself or the combination of matrix and embedding happens in the mould. Moulds can be hollow negatives of the part to be produced or they can be positives that are used for spray or hand layup. Spray layup is commonly used to form fibreglass products such as swimming pools. Hand layup is commonly used to create custom carbon fibre car parts. Depending on the production process, the production volume per mould can be low, and labour intensive.

Pultrusion is a continuous process for the forming of composite materials with consistent cross-sections. The term combines the words ‘pull’ and ‘extrusion’. As opposed to extrusion which pushes the material, pultrusion works by pulling the raw materials through a heated steel die using a continuous pulling device. Before the reinforcement is pulled through the die, it is impregnated with for instance a resin as the matrix. Curing of the composite might happen during or after the pultrusion.

In lamination, usually, a fabric (the reinforcement) is impregnated (with a matrix) before being pulled through a set of (hot) rollers. The process can be used to create flexible composite sheets such as those used to form the bottom of pools and ponds. The process can also be used to create more solid products. Formica©️ is a well-known example of that. Formica originally consisted of layers of fabric bonded together with resin. Later, it was made with thick pieces of paper laminated with melamine. These tough substances can resist heat and abrasion. By using paper in its manufacture, it opened a wealth of colour possibilities and proved key to its success. Formica is still used extensively in kitchen counters and cabinet doors.

4.2f.3 | Composition and structure of composites

Concrete is a particle composite material composed of aggregate (sand and small stones) bonded with a fluid cement that hardens over time. Often additives and reinforcements, such as steel bars known as ‘rebar’ are included in the mixture to achieve different properties of the finished material. When these ingredients are mixed together, they form a fluid mass that is easily moulded into shape. Over time the cement forms a hard matrix which binds the rest of the ingredients together into a stone-like material of many uses.

Engineered wood, composite wood, man-made wood, or manufactured boards include range of derivative wood products which are manufactured by binding strands, particles, fibres, or veneers together with additives and adhesives to create a composite material.

Engineered woods include:

MDF
Particle board
Plywood
LVL (laminated veneer timber)
CLT (cross laminated timber)

Fibreglass or Glass reinforced plastic (GRP) is a fibre-reinforced polymer made of a plastic reinforced by fine fibres made of glass. The material comes in sheets, mats or small strands. It can even be sprayed. Like carbon-fibre reinforced plastic, the composite material is commonly referred to by the name of its reinforcing fibres - fibreglass. Benefits of fibreglass:

Very high strength-to-weight ratio.
Corrosive resistant.
Water-resistant.
Relatively cheap to produce.

Charles and Ray Eames were early pioneers of GRP technology. Plastics were struggling for an authentic form during the 1950’s and 1960’s due to reputation of cheap plastic toys.

Fibreglass is now widely used in many applications and products; surfboards, wind turbine blades, kayaks, water slides, auto body parts, helmets and other protective products to name but a few.

Kevlar fabric

Kevlar®️ (para-aramid)[2] is a strong, heat-resistant synthetic fibre. Developed by Stephanie Kwolek at DuPont in 1965 the high-strength material was first used commercially in the early 1970s as a replacement for steel in racing tires. It is typically spun into ropes or fabric sheets that can be used as such, or as an ingredient in composite material components. Its natural toughness helps allow fabrics and threads to stand up to repeated abuse. Kevlar®️ helps minimise vibration transfer and can sustain deformation without breaking. Its very high strength to weight is also an important property.

Carbon Reinforced Plastic (CRP) or Carbon fibre is stiff and strong but very light carbon-fibre (organic polymers consisting of long strings of molecules held together by carbon atoms) reinforced thermoplastic (FRTP). Replacing steel in many applications, it is up to five times stronger and two-thirds lighter. CFRTP can be expensive to produce but is commonly used wherever high strength-to-weight ratio and rigidity are required. Aerospace, automotive, civil engineering, sporting goods and ever-increasing commercial and applications are being found for this amazing material. The binding polymer is often a thermoset resin such as epoxy and the carbon fibre is there for strength and stiffness. Beyond its incredible strength and weight properties carbon fibre products have a distinct aesthetic appeal. Carbon fibre can be moulded into complex shapes, woven into ropes, cable and fabric sheets.

Kevlar and Carbon Fibre are two good examples of fibres that are woven in specific ways to produce very strong textiles. On their own, these fabrics do not possess strength beyond that of any woven fabric, but once they are combined with a resin, their strength can be astonishing.

Carbon fibre fabric

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