Three Types Of Hardness You Should Test For

One of the characteristics that a component might need to be tested for during mechanical testing is hardness. Hardness refers to how resistant an object is to a permanent shape change. For instance, if force is applied to an object and that object does not shatter, this can be an indication that the object is hard. There are three mechanical testing ways that the hardness of a material is measured.

1. Indentation

Indentation refers to how well an object can resist deformation as a result of a load caused by a sharp object. A material is subjected to various loads by sharp objects and the extent to where the object resists indentation is the object's hardness. Resistance to indentation can be essential under applications where the object is likely to be subjected to indentation. For instance, a surface that may come in contact with rotating blades would need to be resistant to indentation.

2. Rebound

Rebound hardness refers to the ability of an object to return to it's original shape while remaining elastic. For instance, when a hammer collides with a nail, it does not brake or bend. A scleroscope is used to measure the rebound hardness of a part. This device drops a diamond-tipped hammer at a fixed height. Then, the rate of deformation is measured to determine how well the material will resist it. 

3. Scratch Resistance

Scratch resistance is one of the most common concerns when performing mechanical tests for hardness. Scratch resistance refers to the ability of the object to resist deformation when exposed to friction. Because mechanical parts will often come in contact with other parts, even if this is not desired, scratch resistance is a useful characteristic. The sclerometer can be used to test the scratch resistance of a part. A diamond is used to scratch the material. Then, the scratch that is made is observed through a microscope. 

If it is discovered that your material is not hard enough for your application, there are fortunately methods that can be used to harden the material. These include:

  • Precipitation hardening
  • Work hardening
  • Martensitic transformation
  • Solid solution strengthening
  • Hall-Petch strengthening

However, if these methods are not able to harden the material to the necessary degree, it may be necessary to find a different material. Hardness is a crucial part of engineering a part and will determine how long before the part will wear out and whether the part will even remain intact under normal operating conditions.