Material Properties Brian Russell

Exam expectations Knowledge about the properties of materials is often tested in the written paper. You are expected to know about paper/card and at least one other material area.

Properties These can be separated into: Mechanical properties Physical properties Working properties

Mechanical Properties These properties are the ones that determine how a material reacts to external forces: Malleability – to withstand deforming under pressure Ductility – to be able to draw or stretch the material out Toughness – to be able to withstand sudden impact Elasticity – to be able to flex and bend Plasticity – to be able to be permanently changed by external forces Hardness – to be able to resist abrasive wear Durability – to be able to withstand wear and tear such as corrosion Stability – to resist changes to size and shape due to environment, such as heat, moisture etc.

Mechanical Properties When thinking about strength we need to consider: Tensile Strength – to resist stretching or pulling forces Compression Strength – to resist pushing or crushing forces Bending Strength – to resist forces which try to bend the material Shear Strength – to resist sliding or cutting forces Torsional Strength – to resist twisting forces

Physical Properties These properties are the ones that refer to the actual matter that forms the material: Fusibility – to be able to melt (turn into a liquid) at a certain temperature Density – mass per unit volume Electrical conductivity – allow current to pass through the material easily Electrical insulators – resist current passing through the material Semi-conductors – allowing current to pass though under certain conditions

Physical Properties Many materials react to heat: Thermal conductivity – how easily heat flows through the material Thermal insulators – prevent heat flowing through the material Thermal expansion – materials generally expand and contract due to changes in temperature

Physical Properties Optical properties are usually simply described by the following terms: Opaque – does not allow light to pass through it Translucent – allows some light to shine through it Transparent – allows light to shine through (clear)

Physical Properties Acoustic properties refer to how materials react to sound: Some materials absorb sound and are good for carpets, floor coverings etc. Sound insulation is a major factor in car design, for example. Some materials reflect sound and are used in places such as concert halls to help to hear the quality of musical performances

Physical Properties Magnetism is a property possessed by some materials: Ferrous metals (those containing iron) are the most common group of materials to have this property.

Destructive Testing These tests are usually undertaken until the material (usually a standard-size test piece) breaks down: Hardness testing – how hard a material is tested by indenting the surface Tensile testing – material is pulled apart to see how much it stretches Impact testing – hitting the material with a known force Wear resistance – rubbing the material surface with an abrasive material Fatigue testing – repeated forces applied

Non-destructive Testing Tests which are usually carried out on the final product but which do not damage the material: Surface crack detection – tapping to hear sound, visual checks for cracks sometimes aided by using acid, for example to clean and highlight flaws Internal defect detection - X-ray methods/Gamma ray methods/Ultrasonic testing are all sophisticated ways of looking inside a material to check for faults

Specifying materials When designing it is often better to specify the material properties you need Then conduct some research to identify the best material for the job Cost and availability will be key factors in your final decisions You will also need to consider the working properties of the materials you have selected.

Working properties These properties relate closely to the mechanical and physical properties of the materials but are probably easier to understand once you start to ask a few questions: How can it be cut and shaped? Can it be moulded or formed? How can it be joined together? How can it be decorated? Does it need protective finishing?

Primary research In your controlled assessment task you my need to carry out some simple tests on materials to establish their mechanical, physical and working properties. Primary research will assist the development of your product as well as giving evidence of your testing and evaluation skills. General information about material properties copied from the internet or books will score you very little credit and are usually a waste of your time!