Here are the questions: it is for the pre-lab Will side bulging resulting from a

Question

Here are the questions: it is for the pre-lab

Will side bulging resulting from a Rockwell impression taken too close to the edge of a specimen result in a hardness number greater or less than the value obtained by a correct procedure? Why is a minimum thickness of at least ten times the depth of the impression required in the Rockwell test? How should the value obtained be influenced by specimens which are too thin assuming they are tested on a heavy anvil which is: Harder than the specimen? Softer than the specimen? Why is a minimum distance of 1/2" required between different hardness test sites? Is a hardness test normally employed because the property of hardness is desired? Explain.

Explanation / Answer

a) If the mpression is taken too close to the edge, then the impression will be more deep because deformations near the edges are more than the bulk. Hence, hardness obtained will be less than the actual.

b) Minimum thickness should be ten times the depth of the impression because, in case of thin specimen, the effect of the material on which the specimen has been placed intrude in the results, the hardness of which is generally much higher than the specimen being tested. So, the result obtaned is harder than actual.

c) Minimum distance of 0.5" is prescribed because if the test conducted within this prescribed limit, then we get the results whch is harder than the actual result. It is so because the previous test compresses the specimen which increases the strength of the specimen in the region upto about 0.5".

d) Yes, these test are conducted to get the hardness of the materials. This test do not give information about the elasticity modulous or ductilty or malleability. Form this test we get the hardness of the material which represents the deformation the materail will have on impacts.

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