2. Hardnessis the resistance of a material to abrasion or
localized plastic deformation 3. Hardness is not necessarily an
indication of strength , although for some materials such as steel,
a harder steel is a stronger steel. 4. A.) Brinell Hardness Test
(BHN) 5. 1.) Brinell Test Method
-
- a.) Press a 10mm (3/8") diameter ball into material with a
known amount of load.
-
- b.) Measure diameter of the indentation.
-
- c.) BHN =Load=2LSurface Area D[D-(D 2 -d 2 ) 1/2 ]
6.
-
-
- L = Load placed on ball, usually 3000 kg , but 1500 kg, and 500
kg can also be used.
-
-
- D = Diameter of steel ball ( = 10 mm)
-
-
- d = diameter of dent, measured by looking thru a Brinell
microscope.
7. 2.) Limitations of the Brinell Hardness Test
-
- a.) Sample must be ten times thicker than the indentation depth
(sample usuallyshould be at least 3/8" thick).
-
- b.) Test is most accurate if the indentation depth is 2.5 - 5.0
mm.Adjust load to achieve this.
-
- c.) Test is no good if BHN > 650
8. 3.) Advantages of the Brinell Test
-
- a.) Widely used and well accepted
-
- b.) Large ball gives good average reading with a single
test.
-
- d.) Easy to learn and use
9. 4.) Disadvantages of the Brinell Test
-
- c.) High initial cost ($5,000)
-
- Error due to operator reading Brinell Microscope (10%max)
10. B.) Rockwell Hardness Test (Hrb,HRc,etc.) 11. 1.) Method 12.
1.) Method
- a.) Select Scale - load and indentor depending on the
scale
- b.) Press a point into material
13. 1.) Method
- a.) Select Scale - load and indentor depending on the
scale
- b.) Press a point into material
14. 1.) Method C.) Machine measures depth of penetration and
computes hardness 15. 2.) Limitations of the Rockwell Test
-
- a.) Sample must be ten times thicker than the indentation
-
-
- depth (sample usuallyshould be at least 1/8" thick).
-
- b.) Test is most accurate if the Rockwell Hardness is
-
- between 0 and 100. Adjust scale to achieve this.
- If Hra > 60, use Hrc scale
- If Hra < 60, use Hrb scale
16.
- c.) Need 3 tests (minimum) to avoidinaccuracies due to
impurities, hardspots.
17. 3.) Advantages of the Rockwell Test
-
- a.) Widely used and well accepted
-
- b.) Little operator subjectivity
-
- e.) Large range of hardnesses (plastics to steels)
18. 4.) Disadvantages of the Rockwell Test
- c.) Initial cost ($5,000)
19. C.) Converting Rockwell Readings to Brinell 20. 21. 1.)
If-20 < Hrc < 40
22. 2.) If40 < Hrc < 100
23. 3.) If35 < Hrb < 100
24. Hardness Conversion 25. Hardness of Plastics From Matweb:
Shore (Durometer) Hardness Testing of Plastics The hardness testing
of plastics is most commonly measured by the Shore (Durometer) test
or Rockwell hardness test. Both methods measure the resistance of
the plastic toward indentation. Both scales provide an empirical
hardness value that doesn't correlate to other properties or
fundamental characteristics. Shore Hardness, using either the Shore
A or Shore D scale, is the preferred method forrubbers/elastomers
and is also commonly used for 'softer' plastics such as
polyolefins, fluoropolymers, and vinyls. The Shore A scale is used
for 'softer' rubbers while the Shore D scale is used for 'harder'
ones. 26. Hardness of Plastics 27. The Shore hardness is measured
with an apparatus known as a Durometer and consequently also known
as 'Durometer hardness'. The hardness value is determined by the
penetration of the Durometer indenter foot into the sample. Because
of the resilience of rubbers and plastics, the hardness reading my
change over time - so the indentation time is sometimes reported
along with the hardness number. TheASTM test number is ASTM D2240
while the analogous ISO test method is ISO 868. 28. Shore
(Durometer) Hardness Testing of Plastics The hardness testing of
plastics is most commonly measured by the Shore (Durometer) test or
Rockwell hardness test. Both methods measure the resistance of the
plastic toward indentation. Both scales provide an empirical
hardness value that doesn't correlate to other properties or
fundamental characteristics. Shore Hardness, using either the Shore
A or Shore D scale, is the preferred method forrubbers/elastomers
and is also commonly used for 'softer' plastics such as
polyolefins, fluoropolymers, and vinyls. The Shore A scale is used
for 'softer' rubbers while the Shore D scale is used for 'harder'
ones. The Shore hardness is measured with an apparatus known as a
Durometer and consequently also known as 'Durometer hardness'. The
hardness value is determined by the penetration of the Durometer
indenter foot into the sample. Because of the resilience of rubbers
and plastics, the hardness reading my change over time - so the
indentation time is sometimes reported along with the hardness
number. TheASTM test number is ASTM D2240 while the analogous ISO
test method is ISO 868. The results obtained from this test are a
useful measure of relative resistance to indentation of various
grades of polymers. However, the Shore Durometer hardness test does
not serve well as a predictor of other properties such as strength
or resistance to scratches, abrasion, or wear, and should not be
used alone for product design specifications. As seen in the charts
below, the correlation between the two Shore Durometer hardness
scales is weak; attempts at conversion between the scales are
therefore discouraged. The correlation is higher for materials with
similar resiliency properties, but is still too low for reliable
conversions. Likewise, conversion between ShoreHardness and
Rockwell hardness is discouraged. The results obtained from this
test are a useful measure of relative resistance to indentation of
various grades of polymers. However, the Shore Durometer hardness
test does not serve well as a predictor of other properties such as
strength or resistance to scratches, abrasion, or wear, and should
not be used alone for product design specifications. As seen in the
charts below, the correlation between the two Shore Durometer
hardness scales is weak; attempts at conversion between the scales
are therefore discouraged. The correlation is higher for materials
with similar resiliency properties, but is still too low for
reliable conversions. Likewise, conversion between ShoreHardness
and Rockwell hardness is discouraged. 29.
