About Knoop Testing

Microhardness testing is performed by pressing an indentor of a specified geometry into the test surface. Unlike Rockwell testing, the Knoop test only applied to a single test force. The resultant impression or un-recovered area is then measured using a high powered microscope in combination with filar measuring eyepieces, or more recently, automatically with image analyzing software. The Knoop diamond produces an elongated rhombic based diamond shaped indent with a ratio between long and short diagonals of about 7 to 1. Knoop tests are typically performed at test forces from 10 - 1000 g, are often referred to as mainly known as microhardness or microindentation tests and are best used in small test areas or on brittle materials as minimal material deformation occurs on the short diagonal area.

The measured area is used in a formula that includes applied force to determine a hardness value. Tables or automatic electronic or imaging measurements are a more common and convenient way to generate Knoop hardness numbers.