Knoop Hardness Tester

A Knoop hardness tester is used to measure the hardness of brittle materials or thin sections, such as ceramics, glass, and coatings. It is particularly useful for materials that might crack or deform under heavier loads used in other hardness tests.

The Knoop test involves pressing a rhombic-shaped diamond indenter into the material's surface under a specific load. The length of the long diagonal of the indentation is measured, and the Knoop hardness number (KHN) is calculated based on the applied load and the indentation size.

The Knoop test is advantageous for its ability to test very small or thin samples and its suitability for brittle materials. It requires minimal sample preparation and provides precise hardness values with minimal risk of cracking the specimen.

Both Knoop and Vickers tests use diamond indenters, but the Knoop indenter is elongated, producing an indentation with a longer diagonal, which is measured. Knoop is preferred for anisotropic materials and thin films, while Vickers is better for isotropic materials and thicker samples.

Accuracy can be influenced by the surface preparation of the specimen, the precision of the indentation measurement, and the alignment of the indenter. Proper calibration and maintenance of the testing equipment are also crucial for obtaining accurate results.