Uncertainty calculations and calibration of metal hardness testing equipment

Hardness tests have vital role for industries such as aerospace, ground vehicles and energy. In these industries, companies do not have only their internal processes but also sub-contractors. Therefore, for acceptance tests, hardness testing becomes so convenient way in order to confirm conformance of incoming materials to the facility. Additionally, there are also critical test limits that comes from technology transfer projects. In these type of projects, specification limits can be very narrow and design of parts may not be changed and quality (non-conformance) decisions may not be taken as rework or used as. In case of probable failure, material parts could cause catastrophic results in mentioned industries. In this study, hardness test capability of a Vickers Hardness Machine is investigated by use of direct and indirect calibration methods. Uncertainty calculations are made for Vickers test system. While making calibration of hardness test machines, the parts which are components of hardness scales shall be also calibrated / verified. These components must be in necessary tolerances related to EN/ISO specifications. After that, calibration of these hardness test machines are made by use of hardness reference blocks that are produced and calibrated by national metrology institute or an accredited laboratory.