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Hardness, toughness and strength compared

Short answer

Hardness is surface resistance to indentation (e.g., glass is hard but brittle). Toughness is energy absorbed before fracture (e.g., mild steel is tough). Strength is maximum stress a material can bear (e.g., high-tensile steel is strong). They are distinct properties.

What is the difference between hardness, toughness and strength of a material? Explain with example.

  • Hardness is resistance to scratching or indentation of the surface.
  • Toughness is the energy absorbed up to fracture (area under the stress-strain curve).
  • Strength is the maximum stress a material can carry before failure.
BasisHardnessToughnessStrength
MeaningSurface resistance to scratch or indentationEnergy absorption before fractureLoad-carrying capacity per unit area
MeasureMohs, Brinell, RockwellCharpy or Izod impact test, area under curveStress in N/mm2\text{N/mm}^2
Depends onSurface/atomic bondingStrength together with ductilityComposition, microstructure and heat treatment
ExampleGlass is hard but not toughMild steel is toughHigh-tensile steel is strong

For example, a diamond is very hard but brittle, rubber is tough but not hard, and concrete has high compressive strength but low toughness.

✓ Answer checked by Claude Opus 5.5 (high effort)

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