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Chapter 17: D. Testing Methods 193
F
Indentation
Figure 17.14 Brinell hardness test method.
Brinell
This type of hardness test is based on applying forces on an object using a steel
or carbide ball with a 10 mm diameter and subjected to a load of 6614 pounds,
which can be reduced for softer material to avoid excessive indentation (see Figure
17.14). The diameter of the indentation is measured after a certain amount of time
using a low power microscope, and then the Brinell harness number is calculated
by dividing the load applied by the surface area of the indentation.
“Compared to the other hardness test methods, the Brinell ball makes the
deepest and widest indentation, so the test averages the hardness over a wider
amount of material, which will more accurately account for multiple grain structures
and any irregularities in the uniformity of the material” (Surface Engineering
Forum 2008).
Part III.D.4
Rockwell
The Rockwell hardness test method is also based on applying force on an object to
create an indentation but using a diamond cone or hardened steel ball indenter. A
preliminary force will be applied on the indenter to be forced into the test material
under minor load. When equilibrium has been reached an additional major load is
applied with resulting increase in penetration. When equilibrium has again been
reached, the additional major load is removed leaving the preliminary load as is.
The removal of the additional major load will allow a partial recovery. The indentation
from that load is measured and is used to calculate the Rockwell hardness
number.
Advantages of the Rockwell hardness method include the direct Rockwell
hardness number readout and rapid testing time. Disadvantages include many
arbitrary nonrelated scales and possible effects from the sample object support