22RPT01 TracInd BVK-H: Traceability for indentation measurements in Brinell-Vickers-Knoop hardness

Material properties are crucial factors in the modern world, influencing products quality, functionality and overall durability. Knowledge of these critical mechanical properties of materials used in a vast array of industrial and consumer products, transportation, construction, healthcare, and advanced manufacturing is essential to preventing health and safety hazards, controlling the costs of production and creating better-designed, more durable and higher quality products. Hardness is an extremely important material property describing a material’s resistance to localized deformation from an indenter pressing or scraping against its surface. It is determined by measuring the indentation size realised on the tested material surface. This can be done by different hardness testing methods, like the Brinell, Vickers and Knoop (BVK) scales. Hardness is not a physical quantity; it is a method-based quantity and thus the definition of the method and the measurands subject to consideration in hardness are very critical. The uniform use and recognition of such methods require the establishment of accurate, reliable and consistent reference standards at the NMI level and a link to end-user measurements for the lowest level tests in workshops, guaranteeing a continuous traceability chain. However, hardness measurement results are frequently inconsistent with the nominal values of the blocks, highlighting the lack of detailed, standardised measurement methodology and instrumentation, although all instruments used are compliant with relevant ISO hardness standards from a length measurement point of view. This can be attributed to a lack of a commonly accepted definition of the measurand (indentation) and uniformity in the methodology used, as well as a lack of traceability between NMIs and from the NMI level to the end user. The project 22RPT01 TracInd BVK-H addresses these challenges by establishing a unified, traceable, and scientifically robust framework for BVK hardness testing. The proposed solution to the problem of inconsistent hardness measurements consists of defining universally agreed-upon definitions for indentation boundaries and measurement conditions, therefore providing a consistent starting point for the propagation down the traceability chain. Building on this, new long-term stable and high-quality reference indentations to be used as transfer standards are being developed. The proposed set of reference indentations will ensure the traceability of real indentation measurements in three dimensions rather than two dimensions as is currently possible, eliminating errors caused by the varying imaging systems and magnifications in use. This is accompanied by the development of advanced uncertainty models for BVK hardness tests, a methodology to ensure traceable measurements from primary standards to the end-user, and automation of hardness measurements in order to address challenges associated with operator subjectivity and significantly enhance reproducibility. The consortium, consisting of leading NMIs, universities and manufacturers, will disseminate the project’s findings to international metrology and standardization organizations, including the CIPM and ISO. Recommendations for next-generation hardness instruments will guide manufacturers, resulting in instruments producing more consistent results and therefore significant advance hardness metrology at all traceability levels. By addressing longstanding inconsistencies in hardness testing, this project is enhancing the scientific rigor of hardness metrology and enabling more reliable uniform testing on a global scale.