There are several hardness scales currently in use, the most common of which are Brinell, Rockwell, Knoop and Vickers. In all cases the hardness is a function of the maximum load and either the contact or projected area, or the depth of the residual impression at load or after unloading. The usually accepted definition of hardness is that it is the resistance of a material to plastic deformation. In the case of hardness numbers derived from measurements under load clearly there is some elastic contribution to the quoted value, but for metallic materials at high loads the error introduced in this way is probably not significant. However, when dealing with materials that exhibit only small amounts of plasticity (ceramics) or when very low load indentation experiments are carried out, the contribution of elastic deformation to the total displacement is significant and, unless corrected, large errors will result. A generally accepted definition of hardness is the maximum load divided by the projected area of the residual indentation after unloading — the Meyer hardness (Meyer, 1908).
KeywordsMaximum Load Indentation Depth Hardness Measurement Area Function Indentation Experiment
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