Hardness Tests

Hardness is the resistance to plastic deformation by indentation. A load is applied to a material to ascertain its ability to resist being permanently deformed. The harder a metal is, the greater its resistance to plastic deformation. Brinell is the measurement of the hardness when a defined load is applied to the surface of a test item via a tungsten ball indenter. Measurement of the diameter of the resultant round impression, as viewed under a measuring microscope, is performed to determine the Brinell Hardness Number. Leeb involves using a calibrated instrument that impacts a spherically shaped carbide ball with a fixed velocity (generated by a spring force) onto a surface of the material under test. The ratio of the rebound velocity to the impact velocity of the impact body is a measure of the hardness of the material. This is the favoured method of onsite hardness testing Rockwell is the measurement of the hardness when a defined load is applied to the surface of a test item via a cone-shaped diamond or ball indenter. Different hardness scales are used for different materials and also hardness ranges within those materials. At the completion of the test cycle, the Rockwell hardness value is read from the appropriate scale on the dial indicator of the machine. Vickers is the measurement of the hardness when a defined load is applied to the surface of a test item via an inverted-pyramid-shaped diamond indenter. Measurements of the resultant diamond impression as viewed under the test machine microscope, is performed to determine the Vickers Hardness Number