- Created by: stormrogersdavis
- Created on: 05-01-19 19:48
Classification of materials
Materials for product design and engineering are generally split into groups or classifications:
- Papers and boards
- Smart materials
- Modern materials
Some materials have more than one classification, for example, metals can be classed as ferrous, non-ferrous or alloy. It is important for a designer and manufacturer to be familiar with each material classification so that they can select the material most suited to a specific application.
Ferrous: A metal-containing mostly iron and carbon. Ferrous metals are magnetic and will rust. These include low carbon steel, medium carbon steel and cast iron.
Non-ferrous: A metal that doesn't contain iron. Non-ferrous metals aren't magnetic and don't rust. These include aluminium, copper, zinc, silver, gold, titanium and tin.
Alloy: A metal made of two or more metals, or combining two or more elements, one of which must be a metal. Alloys can also be sub-classified as ferrous or non-ferrous alloys. The ferrous alloys include stainless steel and die steel. The non-ferrous alloys include bronze and brass.
Example of a metal application
Aluminium is suitable for a drinks can for a number of reasons.
- malleable which allows the can to be deeply drawn into shape
- Lightweight which makes it easier to lift and transport; aluminium adds little to the product weight
- a food-safe material, which means the user will not be poisoned when drinking from the can
- non-ferrous so it will not rust on contact with the liquid in the can
- very easy to recycle and use again for other products because it has a low melting point, therefore saving finite resources
- aesthetically pleasing, with a natural silvery colour, which offers a contemporary clean look to the product.
Hardwood: a wood from broad-leafed (deciduous) trees. These trees are generally slow growing and lose their leaves in the autumn. These include oak, ash, mahogany, teak, birch and beech.
Softwood: wood from a coniferous (cone-bearing) tree. These trees are generally fast growing and tend to be evergreen. These include pine, spruce, douglas fir, redwood, cedar and larch.
Manufactured board: a man-made wood-based composite material. Manufactured boards are available in much larger sizes than solid wood. These include plywood, marine plywood, aeroply, flexible plywood, chipboard and MDF.
Example of a wood application
Teak is suitable for an outdoor garden bench for many reasons.
- contains natural oil resistant to moisture, making it very weather resistant and unlikely to quickly degrade due to the effects of weathering
- contains natural oils which resist acids and alkalis, meaning the bench is unlikely to degrade due to the bird droppings or cleaning detergents
- is hard, meaning it will withstand scratches from items such as buttons on people's jeans when they sit down or move around on the bench.
- is aesthetically
Woods are often used in manufacture because of the natural aesthetics in their grain pattern.
Thermoplastic: a material which can be repeatedly reheated and reshaped, allowing it to be recycled after its initial use. Thermoplastics have long linear chain molecules held by van der Walls forces. These include low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polyethylene terephthalate (PET).
Thermosetting polymer: a material which when heated undergoes a chemical change whereby the molecules form rigid cross-links. Thermosetting polymers cannot be reheated and reshaped, even at very high temperatures. These include melamine formaldehyde (MF), polyester and epoxy resin.
Elastomer: a material which at room temperature can be deformed under pressure and then upon release of the pressure, will return to its original shape. Elastomers have weak bonds which allow them to stretch easily. They can be stretched repeatedly and upon immediate release of the stretch, will return with force to the original length. These include natural rubber and silicone.
Example of a thermoplastic application
Polyethlene terephthalate (PET) is suitable for a drinks bottle because it is:
- a thermoplastic which allows it to be recycled, this is important for a single use product as it means it will not contribute to landfill
- tough, if the user drops the bottle, the contents will not be released
- available in transparent form, which allows the user to see how much drink is left
- impermeable to carbon dioxide, making it ideal for carbonated drinks
PET can also be pigmented to give the bottle colour and identify the drink, for example, green pigment for a carbonated water drink.
Example of a thermosetting plastic application
Melamine formaldehyde (MF) is suited for a kitchen worktop because it:
- is a thermosetting polymer with a high melting point, so it will not be affected by hot pans placed on the surface
- is chemical resistant which allows the worktop to be cleaned with detergent
- is hard which enables the user to clean the surface with a scouring pad without scratching the surface
- can be pigmented to give the kitchen worktop a specific colour to fit with the kitchen aesthetics
Example of a elastomer application
Neoprene is suitable for a wetsuit because it:
- is an elastomer so the wetsuit will stretch and release to fit tightly around the body
- has good degradation resistance so it will not be damaged by salt water in the sea
- can be pigmented to give a particular colour choice for the consumer or to provide a company brand colour option
Papers and boards
Papers and board
Papers and boards can be described as compliant materials, meaning that they can be scored, folded and cut with the basic tooling to form items such as nets for packaging. These include layout paper, cartridge paper, tracing paper, bleed proof paper, treated paper, watercolour paper, corrugated card, bleached card, mount board, duplex card, foil backed and laminated card.
Example of a paper and board application
Corrugated card is suitable for a takeaway food container like a pizza box because:
- it is compliant and easy to cut and fold to a box shape using a die cutter
- it is a food safe material, the pizza will not be contaminated by the corrugated card
- it is an insulating material due to the air pockets within the corrugations, which will help to keep the pizza warm
- it is a lightweight which makes it easy to carry on a delivery bike
- a pizza box is a single-use product and corrugated card is easily recycled, so the box should not contribute to landfill
- it is biodegradable, so will not contribute to landfill issues if it is thrown away and not recycled
Composites is a material comprised of two or more different materials, resulting in a material with enhanced properties. Composites can be:
- fibre based (CFRP, GRP, fibre concrete)
- particle based (tungsten carbide, concrete)
- sheet based (aluminium composite board, engineering wood, e.g, glulam)
These include carbon fibre reinforced plastic (CFRP), glass fibre reinforced plastic (GRP) and concrete.
Example of a composite application
GRP (glass reinforced plastic) is suitable for a boat hull because it:
- can be manufactured via lay-up method, allowing complex 3D shapes such as the hull to be created
- can be pigmented to produce a range of colours for improved aesthetics or corporate branding such as racing team colours
- has chemical resistance so it won't corrode or decay when in the salty sea water
- is a tough material and able to withstand minor impact from waves, etc without damage
A smart material is a material whose physical properties change in response to an input or change in the environment, such as electricity, pressure, temperature or light. These include shape memory alloys (SMA), thermochromic pigment, phosphorescent pigment and photochromic pigment.
Example of a smart material application
Thermochromatic film is suitable for thermometers because:
- it changes colour in response to temperature change
- the colour change, such as red for hot, makes it easier to read than small numbers or lines as used on traditional thermometers
- it is a non-toxic material, therefore much safer to use than mercury thermometers, for example for taking the temperature of a young child
- it can be incorporated into a film *****, making it flexible enough to go on to a forehead when taking a temperature reading
A modern material is a material developed through the invention of new or improved processes, e.g. as a result of man-made materials or human invention. Modern materials are not 'smart materials' because they do not react to external change. These include kevlar, precious metal clay (PMC), high-density modelling foam and polymorph.