what is the relation between hardness and stiffness on materials?

Question

what is the relation between hardness and stiffness on materials?

Answer 1

Hardness is measured by the mohs scale with diamond the hardest material. Stiffness is measured by Young's modulus and is a materials ability to deform without breaking.

Answer 2

Hardness is the resistance to permanent deformation. Hardness is a measure of the force (or stress) you need to apply to a material if you want there to be some deformation remaining when you take the force away. It is usually used in the context of indentation, so if the material is not hard enough it would get a scratch or permanent indent.



Stiffness is the relationship between force (or stress) and elastic deformation, i.e. when you take the force away the material returns to its original position.



In general, stiffness = force/displacement or stress/strain



As both hardness and stiffness come from interatomic forces in thematerial, high stiffness tends to be correlated with high hardness, but hardness depends on lots of other factors so mild steel and high-carbon steel have similar stiffness but the carbon steel can be much harder.

Answer 3

Hardness has to do with density and stiffness relates to the flexibility.

Answer 4

hard is "If I hit it with a brick...will it break?", stiffness is "If i get Chuck Norris to bend it, will it snap?".......I can't believe I used Chuck in a reference...oh well, It worked.