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Conceptual Understanding: 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.
At a glance:
high strength-to-weight ratio
high tensile strength
weave of the cloth can be chosen to maximise strength and stiffness of final component
can be woven in different patterns to create aesthetically pleasing surface patterns
are much stronger than the original material used. Laminated glass for example is much tougher, and shatters less
corrosion and chemical resistance
very expensive
requires specialist manufacturing facilities
weak when compressed, squashed, or subject to a high shock or impact
small air bubbles or imperfections of the matrix will cause weak spots and reduce the overall strength
can not be recycled- e.g. concrete, carbon fibre, fibreglass and thermosets are hard to separate and recycle
high cost of fabrication of composites is a critical issue
Composite Material: Also called composition materials or shortened to composites) are materials made from two or more constituent materials with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure. The new material may be preferred for many reasons: common examples include materials which are stronger, lighter or less expensive when compared to traditional materials.
Composite Forms are available in fibres, sheets, particles (reinforcement) or in a matrix (with glue/resin).
One material acts as the matrix, which can be in the form of fibres, sheets or particles with the other as the bonding agent.
What is the Matrix?
The Matrix is the medium that bonds us together. The computer programme that serves as a reality whilst we feed the machine.
-Prabu Weaver '21
Forms
Fibre
Fibres are a filamentous material long in relation to its width and breadth. Fibre-reinforced composites contain fibres, which act as the reinforcing material. The fibres can be short or continuous, randomly aligned such as glass fibre (shown below), or in specific directions, such as carbon fibre.
Fibres are excellent in tension. In an effort to increase the fibres’ compressive strength, the fibres are glued together using Epoxy resin as shown from the inside of the Kayak below.
Sheet
Wide material that is thin. Also known as Laminar/ Laminate consists of two or more layers of material bonded together usually with an adhesive to form a new composite material with improved properties.
The most commonly recognised laminar material is plywood which is made by gluing sheets of thin wood (veneer) together with the grain perpendicular to each sheet which makes it either very rigid or very flexible (depending on thickness of each layer and number of layers).
Laminate Glass is another example of a Laminar Composite Sheet material. Consists of a sandwich of two layers of glass and a polymer interlayer of Polyvinyl butyral (PVB) joined under heat and pressure in a furnace called an autoclave
Particle
The least possible amount. One form of composites is particle-reinforced composites with concrete being a good example. The aggregate of coarse rock or gravel is embedded in a matrix of cement. The image here shows the constituent parts of concrete. Particle-reinforced composites find applications where high levels of wear resistance are required such as road surfaces. The hardness of cement is increased significantly by adding gravel as a reinforcing filler. The principal advantage of particle reinforced composites is their low cost and ease of production and forming.
Chipboard/Particle Board - are chipped wood glued with a resin and baked to produce a composite particle board.
Matrix
The matrix material, also known as the glue or resin (e.g. Epoxy Resin) surrounds and supports the reinforcement materials (e.g. Carbon Fibre) by maintaining their relative positions.
The matrix here is the red stuff, holding the fibres together.
Both the matrix and the fibre make up the mechanical property.
Tricky IB type question:
What is reinforced concrete? Fibre, Sheet, Matrix or Particle?
Process
Weaving
To form (fabric or a fabric item) by interlacing long threads passing in one direction with others at a right angle to them.
A resin is then used to set the fibres in a matrix (see below)
Very rigid/stiff form Flexible in the longitudinal axis
Moulding
Spray-up is carried out on an open mould, where both the resin and reinforcements (glass fibres) are sprayed directly onto the mould.
Moulding
Lay-up is carried out on an open mould, where both the resin and reinforcements (glass fibres) are laid and rolled by hand directly onto the mould.
Pultrusion
A continuous moulding process whereby reinforcing fibres are saturated with a liquid polymer resin and then carefully formed and pulled through a heated die to form an extruded profiled part, such as a channel or I beam.
Filament winding
A continuous stream of fibres are soaked (if wet wound) in resin and are rotated on a spinning mandrel. This is how they make long and large tubing and other cylindrical/ prismatic components such as race yacht masts and pipes.
Lamination
The technique of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance or other properties from the use of differing materials.
Design contexts
Concrete:
Sand, concrete, aggregate and water 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 durable stone-like material with many uses.
Kevlar is a composite material similar to Carbon Fibre and is woven into a cloth which combined with Polyester resin can be moulded into a variety of complex shapes. It can also be woven into fabric cloth to protect the wearer almost like an indestructible net. Kevlar also has a high strength-to-weight ratio and is five times stronger than steel.
Kevlar is used for body protection, such as bullet-proof vests. Military helmet where lightweight properties, comfort and flexibility are important, sports equipment, such as skis, helmets and racquets, where lightweight properties and strength are important
IMG_1184.MOVGlass reinforced plastic (GRP) or Fibre Glass is a composite material made from plastic and fine fibres of glass. It is also known as Fibreglass.The strands are combined with resin (polyester or epoxy resin) to make GRP.
Fibreglass and resin on their own are weak but when combined create a good strength-to-weight ratio material. It is very versatile and can easily be moulded into 3D shapes such as Boat hulls, canoes, car body panels, chemical storage tanks and train canopies.
Engineered wood:
Made by binding or fixing strands, particles of fibres, veneers of boards of wood together with adhesives or other fixing methods to create composite materials.
Laminated veneer lumber (LVL) is an engineered wood product that uses multiple layers of natural timber wood assembled with adhesives. It is typically used for architectural beams.
-Medium Density Fibreboard
-Particle or chipboard
-Plywood
-LVL- laminated veneered timber
-I joists or I beams
Particle board : also known as particleboard and chipboard, is an engineered wood product manufactured from wood chips, sawmill shavings, or even sawdust, and a synthetic resin or other suitable binder, which is pressed and extruded.
Used for cheap flat-pack furniture and usually covered with a plastic or timber veneer to increase aesthetics and durability.
Laminate Plywood: A sheet material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another.
If layers are the same thickness then it makes a rigid plywood. It may be used for wall panelling, flooring and furniture.
Note: The difference between Plywood and LVL: LVL is an engineered wood product that uses multiple layers of thin wood, oriented in the same direction (unlike plywood which is orientated in alternate directions) and assembled with resins. Plywood sheets are used in many areas such as furniture while LVL is typically used for beams and edge-forming material.
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