Hardhetsmåling

Hardhetsmåling, or hardness measurement, is a set of material tests used to determine a material's resistance to permanent deformation. The tests typically involve pressing an indenter into a prepared surface and measuring the size or depth of the resulting impression. Hardness values are widely used as indicators of wear resistance, strength, and machinability, as well as for process control and material selection.

The most common methods are Brinell, Rockwell, Vickers, and Knoop. Brinell uses a hardened ball under a specified load and calculates hardness from the resulting indentation diameter. Rockwell employs a diamond cone or a steel ball and reports a numerical hardness value (such as HRC or HRB) based on indentation depth under predefined scales. Vickers and Knoop use diamond pyramids; Vickers yields HV from the diagonal of the square-based impression, while Knoop yields HK with an elongated indentation suited to thin or brittle samples. Microhardness tests apply lower forces to measure hardness on small areas or thin films, using HV, HK, or similar scales. Shore (durometer) hardness is used for polymers and elastomers, providing Shore A or Shore D values.

Standards and practice: hardness testing follows international standards (ISO, ASTM, JIS) that specify test methods, indenter geometry, loads, and surface preparation. Surface polish and accurate measurement of indentation are essential, as results can be influenced by surface roughness, temperature, and sample geometry. Hardness values are empirical and often correlate with other properties, but they are not direct substitutes for tensile strength or toughness and may vary with material type and microstructure.

Applications and limitations: hardness testing is widely used for quality control, material comparison, and process monitoring. It is most reliable for homogeneous, isotropic materials; heterogeneous or very thin sections may yield misleading results due to indentation size effects or substrate influence.