Scratch hardness: Primarily used to compare the hardness of different minerals. The method involves using a rod with one hard end and the other soft end to scratch the material being tested. The hardness of the material is determined by the location of the scratch. Qualitatively speaking, a hard object produces a longer scratch, while a soft object produces a shorter scratch.
Indentation hardness: Primarily used for metallic materials. The method involves pressing a specified indenter into the material under a certain load. The hardness of the material is compared by the magnitude of localized plastic deformation on the surface. Due to differences in the indenter, load, and load duration, there are various types of indentation hardness, mainly Brinell hardness, Rockwell hardness, Vickers hardness, and microhardness.
Rebound hardness: Primarily used for metallic materials. The method involves dropping a specially designed small hammer from a certain height to impact the sample of the material being tested. The hardness of the material is determined by the amount of strain energy stored (and subsequently released) by the sample during the impact (measured by the rebound height of the hammer).
