knoopthårdhetsprov

Knoop hardness testing is a microhardness testing method used to determine the hardness of materials. It is particularly useful for brittle materials like ceramics, glass, and very hard metals. The test involves pressing a rhombic-based diamond indenter into the surface of the material under a specific load. The indenter has an elongated diamond shape with a pyramid angle of 172.5 degrees between the long diagonals and 130 degrees between the short diagonals.

The load is applied for a specific dwell time, typically 10-15 seconds. After the load is removed, the length of the long diagonal of the resulting indentation is measured using a microscope. The Knoop hardness number (HK) is calculated based on the applied load and the measured length of the indentation. The formula for Knoop hardness takes into account the load in kilograms-force and the indentation length in millimeters.

Knoop hardness testing is a non-destructive testing method, although it does leave a small indentation on the material's surface. It is suitable for testing thin layers, coatings, and materials with a low modulus of elasticity. The test is sensitive to surface preparation, and the specimen surface must be highly polished to obtain accurate results. The indenter's shape allows for deeper penetration with less applied load compared to other indenters, making it ideal for materials susceptible to cracking under stress. The Knoop test is standardized by various organizations, including ASTM and ISO.