What is hardness testing?

Hardness testing basically deals with determining the resistance of a particular material to indentation. In other words, it simply means testing a material’s ductility, strength and capacity to resist permanent deformation.

This test helps you to ascertain whether a material is suitable for a particular purpose as you would want it. Nevertheless, hardness is just a characteristic of a material and not an elementary property of any material whatsoever.

So, at the end of the test there must be qualitative evaluation of the following: the weight of the indenting material, the time taken for the hardness testing, the geometry of the indenter.

The principle behind hardness testing

What does hardness testing typically entail?

Hardness testing of a particular material basically involves exerting an indenter (a harder material of specific dimension) in to the material’s surface. The hardness of the material is calculated by determining the intensity of the penetration of the indenter or by determining the impression left by the indenting material.

Categories of hardness testing

  • The intensity of the indenter penetration. For example, Ball Indentation Hardness, Rockwell Hardness and etc.
  • The impression left by the indenting material. For example, Vickers Hardness, Brinell Hardness and etc.

What is the best way to test hardness?

There is actually no particular method for hardness testing that is absolutely suitable for all materials, since hardness is not an elementary property or characteristic of a material.

Therefore, hardness testing strategies vary. What determine the best way to test the hardness of a material are the thickness of the material and the treatment of heat chosen, among other things.

Rockwell testing

However, Rockwell Hardness Testing is the most popularly used as per ASTM – E18.  It is basically easier to carryout, and more precise than other existing methods, to test the hardness of a material.

The Rockwell method of testing hardness can be used for all metals, except in a case where the test metal geometry or surface conditions would cause much variations;

where there would be indentations that are extremely too large for the method to work; or when the sample indent’ size or sample does not support its use.

For Rockwell Test to be accurate it is necessary the operators as well as the strategies employed are both following adequate test practice and technique.

Why is Rockwell hardness method the best?

  • It is a differential-depth method that eliminates every error that pertains to mechanical imperfections unlike Brinell test.
  • Apart from the fact that it eliminates mechanical errors, it is also more affordable than its counterparts.
  • Rockwell Hardness is quicker than other Hardness testing methods
  • It is the most popularly used.