OCR GCSE DT: Chapter 5: Material Considerations

What is absorbency? Give 3 examples of material types with good absorbance

The ability to soak up moisture

• natural fabrics (cotton, linen, wool)

• cardboard

• porous polymers (foam)

Give a material that has good and bad electrical conductivity

• copper (most metals)

• wood and rubber

Give a material that has good and bad thermal conductivity

• steel (most metals)

• pine (wood)

What is strength?

a material’s ability to withstand forces that try to bend or break it (materials can be able to do this in different ways)

Name and define the 4 main types of strength

• compressive strength - withstanding compressive forces (squashing forces)

• tensile strength - withstanding tension forces (stretching)

• yield strength - withstanding forces before it’s permanently deformed

• impact strength - withstanding sudden forces

What is tensile and compressive strength like in metals?

• they tend to be similar in metals

• tensile strength tends to be higher in timbers and composite materials (polymers, glass fibres) than compressive strength

What is tenacity?

the strength of textiles and fabrics

What is hardness? What do hard materials also tend to be?

• the ability to withstand pressure from cutting, scratching or wear

• these materials tend to be brittle

Give 3 ways of measuring hardness

• scratch hardness

• rebound hardness

• indentation hardness

What is malleability and ductility?

• malleability - the ability to bend a material without breaking or snapping when hammered or rolled into a thin sheet

• ductility - the ability to stretch into a thin wire without snapping

What is elasticity?

the ability to be stretched and then return to its original shape

What is durability?

the ability to withstand wear, pressure or damage

Give 4 materials with high strength : weight ratios

• carbon fibre

• glass fibre

• alloys (titanium) -(especially if reinforced with fibres)

What are fibres?

• long, thin, flexible strands of material (synthetic or natural)

• when fibres of materials are made their properties can change and become better

• they have high strength : weight ratios

What is stiffness?

the rigidity of a material (how much it can resist being deformed)

What is plasticity?

the ability to permanently change in shape when force is applied

What is brittleness?

how easily a material will snap or break when a force is applied which decreases with higher temperatures and is the opposite of ductility

What is corrosive resistance?

refers to a material’s resistance to degradation from elements (oxygen), moisture and other chemicals

Give 4 examples of materials that are susceptible to corrosion

• rust on ferrous metals

• softwoods (unlike oak and other hardwoods that are resistant to rot)

• polymers if exposed to UV light, oxygen, chemicals (chlorine) can swell, crack or break-down

Give an example of an object and its material that can become brittle over time

rubber (polymer) products like tyres

How are things like coats and floaties made waterproof?

natural or synthetic fibres are coated or laminated during manufacture with a waterproofing spray

What do materials with magnetic properties do?

emit forces that attract or repel other materials

What are ferro-magnetic materials?

materials that have been made magnetic artificially

Why is using magnetite better than using ferro-magnetic materials?

the magnetic properties of magnetite don’t fade over time