Historical origins of indentation hardness testing

Although it has been known for thousands of years that materials differ in hardness, quantitative methods of measuring hardness by performing careful indentation experiments only began to be developed during the nineteenth century. At the beginning of the twentieth century, hardness testing machines began to be commercially available. The methods that have persisted to this day may be divided into two broad categories: (1) those where a hardened steel ball or cone is pressed into a surface under a known load; and (2) those where sharp diamonds of various shapes are pressed into a surface also under a known load. An issue that has long been of interest is the relation of hardness to simpler measures of material strength, particularly the tensile strength. The review will cover the development of the various static and dynamic techniques and their subsequent application to a wide range of materials.