Calculating Vickers Hardness Number
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Calculating Vickers Hardness Number

(a) What is technological hardness?
(b) What is Vickers hardness?
(c) A Vickers hardness test made on a steel specimen with a load of 30 kg produces an impression whose diagonal measure is 0.654 mm. Calulate the Vickers hardness number and determine the load that should be used if the hardness of an area 0.050 mm in diameter, in the same piece of steel, is to be measured.

The strings: S7P3A32 (force - push).

The math:
Pj Problem of Interest is of type force (push).

(a) In general hardness, is the strength of the surface of a material. In many instances, the surface strength of a material is significantly different from that of the bulk (e.g. surface-hardened steel).Technological hardness is the resistance of a material to permanent deformation of its surface. The deformation may be a scratching impression, mechanical wear, indentation, or cutting.

(b) Indenters of various geometric shapes are used to test the hardness of the surface of a material. Some of the commonly used shapes are: sphere, cone and pyramid. Vickers hardness is the hardness measured by a square-based pyramid indenter.

(c) As an indenter penetrates the surface of a material, the area over which the force of the indenter acts, increases with the depth of penetration, Consequently, the hardness can be expressed only in terms of force and area. As figure 1.1 shows, the Vickers hardness is expressed in terms of force and area as follows:
Vickers hardness, Hv = P/A = P/d2(2 sin α/2). Where A = d2/(2 sin α/2) and α is the angle between two opposite faces of the pyramid; P is expressed in kilograms and A is expressed in millimeter.

Hv = (1.8544)(30/(0.654)2) = 130.
Load P, to be used for area A = 0.050 mm with same hardness, P = [130(0.050)2]/1.8544 = 0.175225 kg = 175 g.

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