The Rockwell hardness test, the Rockwell principle and the variant to the Rockwell principle
The Rockwell Hardness Test
The Rockwell hardness test is one of the main penetration hardness tests currently used, comparable in importance to the Brinell and Vickers hardness tests. Most of the hardness tests are based on the detection of the deformation impressed by a specific penetrator in the material under test. Unlike the Brinell and Vickers tests, which involve the measurement of the indentation following the penetration process, the Rockwell hardness test is based on the difference in depth impressed by the indenter at two different times in the test cycle.
The Rockwell process
The Rockwell test procedure applies to all Rockwell scales and is independent of the type of indenter and load used. An initial force called preload is applied to the indenter, which is placed in contact with the material to be tested, with the aim of eliminating the effect of surface imperfections on the measurement: the depth achieved by applying preload is therefore the starting point of the measurement. Then, the load is applied (determined on the basis of the chosen scale, depending on the material under test) which is added to the preload and is kept constant for a certain period of time, during which the material undergoes an elasto-plastic deformation. The load is then removed, leaving only the preload and allowing the material to cancel the elastic deformation and to highlight only the plastic deformation that is the object of the hardness measurement.
The Rockwell variant
Most of our Rockwell instruments operate according to a variant of the Rockwell principle, aimed at neutralizing the effects of possible bending or failure of the surface under test. It is an additional element that "follows" the surface in its movements, takes it into account and eliminates its effects on the measurement.
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