How do you choose the best hardness test method for different materials?

2 Brinell hardness test

The Brinell hardness test is another common hardness test method, especially for metals with coarse or heterogeneous structures, such as cast iron, steel, or aluminum. It involves applying a constant load to a material using a hardened steel or carbide ball indenter, and measuring the diameter of the indentation. The hardness value is calculated from the ratio of the load to the surface area of the indentation, and is expressed as a number followed by HB or HBW. The Brinell hardness test can be used for large or irregular samples, and it has some advantages, such as low sensitivity to surface conditions, easy comparison of results, and good correlation with tensile strength. However, it also has some drawbacks, such as the need for high loads and large indenters, the difficulty of measuring the indentation accurately, and the potential for plastic deformation or residual stress.

3 Vickers hardness test

The Vickers hardness test is a more refined and precise hardness test method, suitable for thin or small samples, or for measuring the hardness of individual microstructures or phases. It involves applying a fixed load to a material using a diamond pyramid indenter, and measuring the diagonal length of the indentation. The hardness value is calculated from the ratio of the load to the surface area of the indentation, and is expressed as a number followed by HV or GPa. The Vickers hardness test can be used for metals, ceramics, composites, and coatings, and it has some benefits, such as the independence of the scale and indenter size, the high resolution and accuracy of the measurement, and the ability to perform microhardness testing. However, it also has some challenges, such as the need for careful sample preparation, the difficulty of aligning and positioning the indenter, and the influence of elastic recovery or edge effects.

4 Knoop hardness test

The Knoop hardness test is a variation of the Vickers hardness test, designed for very thin or brittle materials, or for measuring the hardness of specific features or regions. It involves applying a low load to a material using a diamond rhombic indenter, and measuring the long diagonal length of the indentation. The hardness value is calculated from the ratio of the load to the surface area of the indentation, and is expressed as a number followed by HK or GPa. The Knoop hardness test can be used for metals, ceramics, glass, minerals, and biological materials, and it has some advantages, such as the low load and indenter size, the minimal damage or deformation to the sample, and the ability to perform microhardness testing. However, it also has some limitations, such as the need for high magnification and precision of the measurement, the asymmetry and non-uniformity of the indentation, and the dependence of the results on the orientation and anisotropy of the material.

5 Shore hardness test

The Shore hardness test is a simple and convenient hardness test method, mainly used for rubber, elastomers, plastics, and foams. It involves applying a spring-loaded indenter to a material and measuring the depth of penetration. The hardness value is expressed as a number followed by a scale letter, such as A, D, or O. The Shore hardness test can be used for flexible or soft materials, and it has some benefits, such as portability and ease of use, quick and non-destructive testing, and wide range of scales and indenters. However, it also has some disadvantages, such as low accuracy and repeatability, high variability due to temperature and time effects, and poor correlation with other hardness scales or mechanical properties.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?