Hardness is an important property of a material, but it has no specified physical meaning. Many authorites give different definitions to it conventionally, but it should be noticed that the relative values among the hardness numbers of different materials are more important than their absolute values, The following two important proposals as to the definition and the scale of hardness are given. (i) The hardness of a material is the resistance to the compressive deformation due to a given tool. (ii) The hardness no is defined as the amount of energy obsorbed plastically by a unit volume of the indentation produced by a tool. Therefore we have the following equation. -II=Wp/Vp where H=Hardness no, Wp=Energy absorbed plastically in kg-mm, Vp=Plastic indentation volume in mm^3. Wp is measured by the area multiplied by a certain scale constant in the load indentation diagram, and Vp is the volume of the indentation after the load removed. The chief objects of the researches are as follow : (i) to find the relation between the hardness no. and the load applied, and (ii) the relation between the hardness no. and the diameter of the ball used. With the definition and scale of hardness as above mentioned we shall study the two relations described above.
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