Hardness is a measure of how resist solid matter is to various kinds of permanent shape change when a force is applied.

Hardness testing by Indentation method (Brinell Hardness Test)

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. The tests work on the basic premise of measuring the critical dimensions of an indentation left by a specifically dimensioned and loaded indenter.

Hardness testing by Rebound method (Leeb rebound Hardness Test)

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 testing by Ultrasonic method (Ultrasonic Hardness Test)

Instead of measuring the size of the indentation of the test sample using a microscope, it uses a diamond indenter equipped with a vibrating rod that presses on the test surface at a fixed load and then measures its hardness by applying ultrasonic vibrations and analyzing its damping effect.