Hardness

Hardness is a measure of the resistance of a material to surface indentation or abrasion. It can be defined in various ways depending on the specific application. In the context of materials science, hardness is the property that enables a material to resist deformation, bending, scratching, abrasion, or cutting.

Definition

Hardness is not a fundamental property of a material, but rather a response to a specific test method. Hardness values are arbitrary, and there are no absolute standards for hardness. Hardness is a complex property that can be defined in different ways. It is dependent on the material's elastic modulus, ductility, plasticity, strain, strength, toughness, viscoelasticity, and viscosity.

Measurement

There are three main types of hardness measurements: scratch, indentation, and 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.

Scratch Hardness

Scratch hardness is the measure of how resistant a sample is to fracture or permanent deformation due to friction from a sharp object. The principle is that an object made of a harder material will scratch an object made of a softer material.

Indentation Hardness

Indentation hardness measures the resistance of a sample to material deformation due to a constant compression load from a sharp object. They are primarily used in engineering and metallurgy fields.

Rebound Hardness

Rebound hardness, also known as dynamic hardness, measures the height of the "bounce" of a diamond-tipped hammer dropped from a fixed height onto a material. This type of hardness is related to elasticity.

Hardness in Materials

Hardness is important from an engineering standpoint because resistance to wear by either friction or erosion by steam, oil, and water generally increases with hardness. The hardness of a material is directly related to its inelastic response to an applied stress.

See Also

• Mohs scale of mineral hardness
• Vickers hardness test
• Brinell hardness test
• Rockwell hardness test
• Shore durometer hardness scale

References

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Hardness

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  Vickers tester
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  Stress-strain curve
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  Close-packed spheres
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  Dislocation edge