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 FAQ
A: Yes, so the distance near an edge or an adjacent indent is critical. ASTM recommends the
distance from the center of an indentation and the nearest adjacent
indentation be 3 times the diameter of the indentation. The distance between
the center of an indentation to the nearest edge must be at least 2.5 times the diameter of the indentation.
A: Material surrounding the indentation is plastically
deformed well below the indentation depth. If the material is too thin the
deformation will flow into the anvil which could cause erroneous readings...
A: HRA scale, which uses a diamond indenter with a 60kg weight
is recommended. A diamond indenter is not likely damaged by penetrating too
deeply into soft material, whereas a ball indenter may be flattened or damaged
if the material is too hard.
A: Micro indentation uses loads from 10grams to
1000grams. Macro indentation uses loads above 1000 grams.
A: When using a diamond indenter scales the
infinite hardness number is 100. When using a ball indenter scales the
infinite hardness number is 130.
A: One Rockwell number represents a penetration of 0.002mm (0.000080 in.)
Therefore, a reading of HRC 60 indicates
a penetration from minor to major load of (100 - 60) X 0.002mm = 0.080 mm or
0.0032 in. A reading of HRB 80 indicates a penetration of (130 - 80) X 0.002
mm = 0.100 mm or 0.004in. Note: The numbers 100 and 130 above are the infinite
hardness numbers for those scales.
A: The Knoop indenter is an accurately ground diamond forming
a rhombic based pyramid. An indent seen perpendicular to the specimen surface
is rhombic in outline with diagonals having an approximate ratio of 7 to 1.
Because of the Knoop indenter's geometry, indents of accurately measurable
lengths are obtained with light loads...
A: One Superficial Rockwell number represents a penetration of 0.001 mm or 0.000040 in.
Therefore, a reading of 30N80 indicates a penetration from minor to major load
of (100 - 80) X 0.001 = 0.020 mm or 0.0008 in. Note: The number 100 used in
the calculation is the infinite hardness number used for all Superficial
scales.
  A: The infinite hardness number is 100 for all Superficial hardness scales.

A: At the low hardness end of a ball scale the ball may penetrate too deeply causing the cap to come into contact
with a specimen which would damage the cap...

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