Definition - What does Hardness mean?

Hardness is defined as the ability of a material to resist plastic deformation, usually by indentation. The term may also refer to resistance to:

  • Scratching
  • Abrasion
  • Cutting
  • Penetration

It is the property of a metal which gives it the ability to resist being permanently deformed when a load is applied. Therefore, hardness is important from an engineering standpoint because resistance to wear by either friction or erosion by various elements generally increases with hardness. The greater the hardness of the metal, the greater resistance it has to deformation.

Corrosionpedia explains Hardness

Hardness is the resistance of a material to localized deformation. Hardness can apply to deformation from many factors, including:

  • Indentation
  • Scratching
  • Cutting
  • Bending

Hardness is dependent on:

  • Ductility
  • Elastic stiffness
  • Plasticity
  • Strain
  • Strength
  • Toughness
  • Viscoelasticity
  • Viscosity

Hardness measurements are widely used for quality control of materials because they are quick and considered to be nondestructive tests when the marks or indentations produced by the test are in low-stress areas.

Important hardness measurements are:

  • Scratch hardness - This measures how resistant a sample is to fracture or permanent plastic deformation due to friction from a sharp object. The Mohs scale is used to measure it.
  • Indentation hardness - This measures the resistance of a sample to material deformation due to a constant compression load from a sharp object. Indentation hardness scales are Rockwell, Vickers, Shore and Brinell.
  • Rebound hardness - This measures the height of the "bounce" of a diamond-tipped hammer dropped from a fixed height onto a material. The Leeb rebound hardness test and Bennett hardness scale are used to measure rebound.

Within each of these classes of measurement there are individual measurement scales. For practical reasons conversion tables are used to convert between one scale and another.

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