HARDNESS TEST
Hardness may be defined as resistance of metal to deformation usually by indentation. The term may also refer to stiffness or temper or to resistance to scratching, abrasion or cutting.
Indention hardness may be measure by various hardness tests. They are.
(1) Brinell Test
(2) Rockwell Test
(3) Vicker Test
(1) Brinell Test :-
It consist of pressing a harden steel ball into a test specimen. According to ASTM specification a 10mm diameter ball is used for the purpose. Lower loads are applied for measuring hardness of soft material and vice verse (Click here for more......)
(2) Rockwell Test:-
Rockwell hardness test is based on the indentation of a hard tip brale or indenter into test piece under the action of two consecutively applied loads, Minor [initial] and major [final]. In order to eliminate zero error and possible surface effect due to roughness or scale, the initial or minor load is first applied and produces and initial indentation.
A conical shaped diamond called Brale with 120o apex angle and 0.2 mm radius is used as the indentor or penetrator in the Rockwell test for hard materials. For soft material a hardened steel ball 1.2mm in diameter is generally used.
Rock well testing is faster as compared to Brinell testing because diameter of indentation need not be measured. The Rockwell machines give arbitrary direct reading (Click here for more......)
(3) VickerTest :-
The test is similar to that of the Brinell in that the hardness no: is derived from the relationship between the applied load and the surface area of the indention.The test insists in forcing the square base diamond pyramid (with an angle 136o between the opposite faces) into the ground or even polished surface to be tested.The applied load is 5,10,30,50,100 or 120 kg. (Click here for more......)
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