Materials
The material types used in engineering are woods, metals, plastics, ceramics and composites. Each of these has its own
characteristic working properties such as strength, malleability, conductivity, toughness and durability.
Types of materials
You need to be familiar with the different properties of ferrous and non-ferrous metals; softwood and hardwood
timbers; and thermoplastics and thermoset plastics.
When working with resistant materials you need to be able to choose the best material for a job. Wood, metal and plastics
are the most common materials used, followed by composites and ceramics.
The main classification of materials is given in the chart below. You need to know these terms and their definitions.
Material classification diagram
Plastics
Plasics are divided into thermoset plastics and thermoplastics. The main difference between the two is that thermoplastics
can be heated and shaped many times, while thermoset plastics can only be heated and shaped once.
Composite materials
Composite materials are formed by combining and bonding two or more materials - a reinforcing material and a bonding agent
such as glue. MDF and GRP are examples of composite materials. NB alloys are not composite materials.
Metals
Metals can be either ferrous or non-ferrous. Ferrous metals contain iron while non-ferrous metals do not.
Both ferrous and non-ferrous metals are divided into pure metals and alloys. A pure metal is an element - eg iron, copper,
gold - unalloyed (not mixed) with another substance. An alloy is a mixture of two or more elements (eg, iron and carbon) to
make another metal with particular properties (eg steel).
Ceramics
Ceramics are made from clay, sand and feldspar. These materials are ground to a fine powder, mixed together and fired at
high temperatures (700 - 2000°C) in the production process.
Timbers
Timbers are divided into hardwood timbers and softwood timbers. Hardwood timbers get their name because of their
cellular structure when seen under a microscope - not because they are hard to cut. Softwoods do not have this same hard
cellular structure.
Working properties
Different materials exhibit different working properties. Listed below are the key properties which determine how materials
behave. You need to know what each of these terms mean.
Conductivity
The ability of a material to conduct heat or electrical energy.
Strength
The ability of a material to withstand a force without breaking or bending.
Elasticity
The ability of a material to bend and then to return to its original shape and size.
Plasticity
The ability of a material to permanently change in shape.
Malleability
The ability of a material to permanently deform in all directions without cracking.
Other terms you should know
" Ductility is the ability of a material to deform, usually by stretching along its length.
" Hardness is the ability of a material to resist wear, scratching and indentation.
" Toughness is the ability of a material to withstand blows or sudden shocks without breaking.
" Durability is the ability of a material to withstand wear, especially as a result of weathering.
" Fusibility is the ability of a material to change into a liquid or molten state when heated to its melting point.
Metals
Ferrous metals
Ferrous metals contain iron. Examples are cast iron, mild steel, medium carbon steel, high carbon steel, stainless steel, and
high speed steel.
Composition, properties and uses of some common ferrous metals
Non-ferrous metals
Non-ferrous metals do not contain iron. Some common non-ferrous metals are aluminium, duralumin, copper, zinc, brass,
gilding metal and tin.
Composition, properties and uses of some common non-ferrous metals:
Timbers
There are two types of timber: softwood and hardwood.
Softwood timbers usually come from coniferous trees - that is, evergreen, needle-leaved, cone-bearing trees such as fir and
pine. They do not have the hard cell structure that gives hardwood trees their name.
Hardwood timbers come from broad-leaved, deciduous trees, and are more important in Design and Technology than
softwood timbers. The main hardwood timbers are ash, beech, birch, cherry, elm, iroko, mahogany, meranti, oak, obeche,
sapele and teak.
The table lists the properties and uses of these hardwood timbers.
Plastics
Thermoplastics
Thermoplastics can be heated and shaped many times. Some common thermoplastics are ABS (acrylonitrile butadienestyrene),
Nylon (polyamide), acrylic (polymethyl methacrylate), uPVC (polyvinyl chloride), polystyrene, polypropylene and
cellulose acetate.
The table lists the properties and main uses of thermoplastics.
Thermoset plastics
Thermoset plastics can only be heated and shaped once. The main thermoset plastics are epoxy resin, melamine
formaldehyde, polyester resin and urea formaldehyde.
The table explains the properties and uses of the main thermoset plastics.