ME 111L Lab Unit 2 Knoop Micro

ME 111L Lab Unit 2 Knoop Micro - The elongated diamond...

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Usman Ansari ME 111L Lab Unit 2 Knoop Microhardness Results One fundamental difference between Rockwell hardness testing and Knoop hardness testing is the specific total test force. For standard Rockwell hardness testing, a specific total test force of usually either 60 kgf, 100 kgf, or 150 kgf is applied after the preliminary test force of 10 kgf. Even for the Rockwell Superficial hardness test the specific total test force is usually either 15 kgf, 30 kgf, or 45 kgf and is applied after the preliminary test of 3 kgf. On the other hand, the specific total test force for the Knoop Microhardness test is usually 50 gf to 1000 gf, which is much smaller than any of the Rockwell test forces. Knoop microhardness testing is preferred over Rockwell hardness testing for brittle or thin sheets since only a very small indentation can be made to test the hardness.
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Unformatted text preview: The elongated diamond indenter and low test forces allows testing very small parts. Also only a very small sample of material is required for testing and it is valid for a wide range of test forces. Another reason Knoop is preferred is because its test allows for distinguishing the hardness between phases and microconstituents in the solid, as to where Rockwell testing only provides a bulk hardness of the solid. • The Knoop indenter makes a very small indentation that can only be measured under a microscope. The optical microscope is used to measure the longest diagonal of the diamond shaped indent. The long diagonal is approximately .001 to .200 mm. • Hardness number = 14229 * Test Force / (Long diagonal Length)^2 Test Force = Hardness Number * (Long diagonal Length)^2 / 14229 Test Force = 540 HK * (100 μm)^2 / 14229 Test Force = 379.5 gf...
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