This mini-lesson covers the Performance Characteristics of Materials: the mechanical and physical properties you use to select and justify materials, the forces and stresses products must resist, and how properties can be enhanced.
You will define strength, hardness, toughness, ductility, malleability, elasticity and density, meet tension, compression, shear, bending and torsion, and calculate stress and density. Press Start to begin.
Properties · mechanical
Mechanical properties
Mechanical properties describe how a material behaves under a force. You must define and compare them precisely.
Tensile strength — resistance to being pulled apart (tension).
Compressive strength — resistance to being crushed (compression).
Hardness — resistance to scratching, indentation and wear.
Toughness — ability to absorb impact/energy without fracturing (opposite of brittle).
Ductility — ability to be drawn into wires (deform in tension without breaking).
Malleability — ability to be pressed/hammered into thin sheets without cracking.
Elasticity — ability to return to original shape after a load is removed; plasticity is permanent deformation.
Do not confuse:hard (resists scratching) is not the same as tough (resists impact). Cast iron is hard but brittle; mild steel is softer but tough.
Quick check
Drawn into wire
?Copper is drawn into long thin wires for cables. Which property makes this possible, and how does it differ from malleability?
Properties · physical
Physical properties
Physical properties come from the material itself, independent of applied force:
Density — mass per unit volume (g/cm³ or kg/m³); low density matters for aircraft and sports goods.
Electrical conductivity — how well it carries current (copper high; polymers insulate).
Thermal conductivity — how well it carries heat (metals high; foams low).
Corrosion/oxidation resistance — resistance to chemical attack such as rusting.
Thermal expansion — how much it grows when heated (allowed for in bridges and rails).
Fusibility — the ease with which it melts.
Forces & stresses
Forces and stresses
Products must resist the forces acting on them. The five you must recognise:
Tension — pulling apart (a tow rope).
Compression — squeezing/crushing (a table leg).
Shear — opposing forces sliding past each other (a bolt in a joint, scissors cutting).
Bending — combines tension on one face with compression on the other (a shelf).
Torsion — twisting (a screwdriver shaft, a drive axle).
Stress = force ÷ cross-sectional area (N/mm², equal to MPa). Shapes such as I-beams and tubes resist bending/torsion efficiently for their mass.
Quick check
Which force?
?A shelf bracket loaded with heavy books experiences forces that stretch its lower edge and squeeze its upper edge. Which force is this?
Sort it
Sort the terms
Tap a term, then the group it belongs to.
💪 Mechanical property
🌡️ Physical property
🧭 Type of force/stress
Enhancement
Enhancing material properties
Properties can be improved by processing:
Annealing — heating then slow cooling to soften a metal and relieve stresses (undoes work hardening).
Hardening — heating high-carbon steel then quenching to make it hard but brittle.
Tempering — gently reheating hardened steel to trade some hardness for toughness, removing brittleness.
Case hardening — giving low-carbon steel a hard skin over a tough core.
Work hardening — repeated bending/pressing makes a metal harder but more brittle.
Alloying, lamination (gluing layers, e.g. plywood/laminated beams) and seasoning of timber also enhance performance.
Quick check
Too brittle to use
?A chisel blade is hardened by quenching but is then too brittle and chips. What process restores toughness, and what is the trade-off?
Match it
Match each property to its definition
Tap an item on the left, then its match on the right.
Property
Definition
Calculate
Your turn — calculate stress
1A tie bar has a cross-sectional area of 20 mm² and carries a pull of 4000 N. Stress = force ÷ area. Calculate the tensile stress in N/mm².
N/mm²
Hint: stress = 4000 ÷ 20.
Calculate
Your turn — calculate density
2A metal block has a volume of 50 cm³ and a mass of 135 g. Density = mass ÷ volume. Calculate its density in g/cm³ (this identifies it as aluminium).