Hardness, Hardness Tests And Hardness Conversion Tables
Hardness has been variously defined as a solid materials resistance to abrasion, penetration, scratching, tear or wear. This proves that hardness is not an inherent property of a material rather the result of a defined measurement procedure carried out as part of hardness tests.
The ideal method to arrive at the Hardness Value of a material is to measure the depth/ area of the indentation produced by an indenter of a definite shape when a specific force is applied on it for a specified period. This relationship between hardness and the size of the impression is usually established using three standard test methods, known as the Brinell, Vickers, and Rockwell tests.
Each one of these test methods makes use of a definite scale (which is dependent on the applied load and indenter-shape) for calibration purpose. Thus, the Brinell Hardness Scale gauges the hardness of metals. Similarly, the Rockwell Hardness Scale measures different materials, right from soft bearing metals to carbides and the Vicker's Scale measures the hardness of thin materials.
The Hardness scales have another function – individual scales allow conversions to other scales. Thus, according to the Hardness Conversion Table, a Hardness value of 36 in the Rockwell (Diamond Brale) C Scale is equivalent to the following Hardness Values:
52 in the Rockwell (Diamond Brale) D Scale, 109 in the Rockwell (1/16" Bull) B Scale, 331 in the Brinell Scale (using a 10 m/m Ball) and 354 in the Vickers Scale.
Remember that all these hardness values have been arrived at by using varying weights.
In actuality, there exists no relationship between the results of different hardness tests since most materials show different behaviors under different measurement tests and conditions. Use of different weights as well as of indenters (of various shapes and sizes) for the different test methods cause hardness conversions to be mathematically inaccurate. The homogeneity of the sample materials and their elastic properties further complicate the problem.
Hardness conversion tables and charts, therefore, should be considered as giving approximate equivalents, rather than precise mathematical equals. This is particularly true when conversion involves a method or scale, which can neither undertake the real test nor verify the test-result.
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Allen is a successful writer and publisher of Hardness Tester related issues, for more informative articles go to www.hardnesstesters.info
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