Which material properties decide whether a material is fit for a job?
Mechanical and physical properties of materials: strength, hardness, toughness, ductility, malleability, elasticity, stiffness, density, conductivity and corrosion resistance.
A CCEA A-Level Technology and Design answer on the mechanical and physical properties of materials - strength, hardness, toughness, ductility, malleability, elasticity, stiffness, density, thermal and electrical conductivity and corrosion resistance - and how they govern material selection.
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What this dot point is asking
CCEA expects precise definitions of the mechanical and physical properties used to select materials, and the ability to link a property to a material and a product. The most-tested are strength, hardness, toughness, ductility, malleability, elasticity, stiffness, density, conductivity and corrosion resistance.
The answer
Mechanical properties
Hardness vs toughness, ductility vs malleability
Physical properties
Worked example: selecting a material from properties
Examples in context
Example 1. Saw teeth. A saw blade is often hardened only at the teeth (hard, wear-resistant edge) while the body stays tougher and more flexible, deliberately combining two properties because a fully hardened blade would shatter.
Example 2. Aircraft skin. Aluminium alloy is chosen for its low density (weight) combined with adequate strength and corrosion resistance, showing that a physical property (density) can dominate the selection.
Try this
Q1. Define ductility. [1 mark]
- Cue. The ability to be drawn out into a wire (to deform plastically under tension) without breaking.
Q2. A material for a cutting tool must keep its edge. Which property is most important, and name a suitable material. [2 marks]
- Cue. Hardness; for example hardened tool steel or tungsten carbide.
Q3. Explain why copper is used for electrical cable. [2 marks]
- Cue. It has high electrical conductivity and is ductile, so it can be drawn into wire easily.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA 20196 marksDefine the terms toughness, hardness and ductility, and for each name a material that exhibits the property and a product that relies on it.Show worked answer →
Toughness is the ability to absorb energy and resist sudden impact or shock without fracturing. Material: mild steel (or many polymers). Product: a hammer head shaft / car body panel that must not shatter on impact.
Hardness is the resistance to surface scratching, indentation and wear. Material: hardened tool steel (or tungsten carbide). Product: a drill bit / file / cutting tool that must keep its edge.
Ductility is the ability to be drawn out into a wire or to deform plastically under tension without breaking. Material: copper (or annealed mild steel). Product: electrical wire / drawn tube.
Markers reward three correct definitions (note toughness is energy absorption/impact, hardness is surface resistance to wear, ductility is drawing into wire under tension), each with an apt material and product. Confusing hardness with toughness is the common error.
CCEA 20214 marksExplain the difference between strength and stiffness, and state why both matter when selecting a material for a diving board.Show worked answer →
Strength is the ability to withstand an applied force without failing (yielding or fracturing). Stiffness is the resistance to elastic deformation, that is how much a material bends or stretches under load (high stiffness means little deflection for a given force, related to the Young modulus).
For a diving board both matter: it must be strong enough not to break or take a permanent set under the diver's weight and the impact of the bounce; but it must also have controlled stiffness - flexible enough to flex and spring the diver up, yet stiff enough not to deflect dangerously far or feel floppy. A material could be strong but too stiff (no spring) or flexible but not strong (it breaks), so the designer balances both.
Markers want strength = resisting failure under load, stiffness = resisting bending/elastic deflection, and a clear reason both are needed (must not break, but must flex in a controlled way).
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Sources & how we know this
- CCEA GCE Technology and Design specification — CCEA (2016)