Hardness
In materials science, hardness is the characteristic of a solid material expressing its resistance to permament deformation.
There are three principle operational definitions of hardness:
- Scratch hardness
- Indentation hardness
- Rebound, dynamic or absolute hardness
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2 Indentation hardness 3 Rebound hardness 4 Bibliography 5 External links |
In mineralogy, hardness commonly refers to a material's ability to penetrate softer materials. An object made of a hard material will scratch an object made of a softer material. Scratch hardness is usually measured on the Mohs scale of mineral hardness. Pure diamond is the hardest known substance so it will scratch any other material. Diamond, being the hardest material, is the substance used to cut diamond. Higher-grade diamonds are used to cut lower-grade diamonds.
Primarily used in engineering and metallurgy, indentation hardness seeks to characterise a material's resistance to permanent, and in particular plastic, deformation. It is usually measured by loading an indenter of specified geometry onto the material and measuring the dimensions of the resulting indentation.
There are several alternative defintions of indentation hardness, the commonest of which are:
Also known as dynamic or absolute hardness, rebound hardness measures the height of rebound of an indenter dropped onto a material using an instrument known as a scleroscope.
Scratch hardness
Indentation hardness
There is, in general, no simple relationship between the results of different hardness tests. Though there are practical conversion tables for hard steels, for example, some materials show qualitativey different behaviours under the various measurement methods.Rebound hardness
Bibliography
External links