Developing traceable automated tests for material hardness
Hardness is a property of all materials and can have a profound impact on the suitability and safety of a material’s use.
Hardness is tested by applying a known load to a sample through an instrument, often tipped with a diamond, to make a permanent indentation. The indentation is then measured across its diameter and a conversion factor is applied to determine the material’s hardness number. Different types of hardness test are suitable for different applications – Brinell, Vickers and Knoop (BVK), which each use a differently shaped indenter, are three of the most commonly used.
However, indentation measurements are mostly still done manually and so accuracy is heavily influenced by the operator. They are also impacted by a lack of standards defining the borders of indentations, a lack of suitable references and poor traceability due to the number of different devices used for testing. A decrease in accuracy has been identified in particular when moving between National Measurement Institutes (NMIs) and testing laboratories.
The project will address these issues by developing a methodology to define indentation borders and producing long-term stable reference indentations for each BVK test. It will also create a methodology for ensuring traceability, alongside design recommendations for manufacturers to implement in future machines. Finally, it will develop software for the automation of indentation measurements.
This work will improve accuracy for BVK tests by removing ambiguity in measurements and reducing reliance on human operators. This will, in turn, improve safety and reduce costs associated with replacing unsuitable materials.