Verification of Knoop indenters with a Vickers-addressed optical system

ISO 4545-2 and 4545-3 of Knoop hardness tests require the geometrical verification of the indenters.INRiM hardness laboratory, in cooperation with Galileo-LTF, has developed the Gal-Indent optical mea-suring system for the verification of Vickers indenters. This system can measure the vertex anglesbetween two opposite faces, the quadrilateral base angles and the pyramid axis tilt angle. Using thesemeasured quantities as inputs of a suitable geometrical model, the angles between the opposite edgesat the vertex of Knoop indenters, nominally 172.5°and 130°, and the angle between the pyramid andindenter holder axes can be verified with an expanded uncertainty of 0.05°. Comparison of experimentalmeasurements performed on three different Knoop indenters, previously verified by an accredited labo-ratory, shows compatible results. The proposed geometrical model could be easily implemented by lab-oratories that adopt similar measuring systems addressed for the verification of Vickers indenterswithout any modification of the experimental apparatus