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3.3 Preparation of the Sample Surface
Preparation for sample surface should conform to the relative requirement in
Appendix Table 3.
• Test surfaces should be at or close to room temperature for optimal
performance
• To eliminate hardness errors resulting from the roughness of a sample’s
surface when using impact device D, DC or D+15, the test surface should be
polished until its roughness Ra is no more than 2
m. PHASE II SRG-2000
handheld surface roughness tester or any other suitable instrument may be
used to measure the surface roughness of the sample material. The test
surface should be clean and free from oil stains.
• Support of test sample. Support is not necessary for heavy samples. Lighter
weight parts must be set on the flat, smooth surface of a larger mass metal
object. The sample must be completely stationary and without any gaps
between the two parts.
• Curved surface: The best testing surface of sample is flat. When the
curvature radius R of the surface to be tested is smaller than 30mm (D, DC,
D+15,C, E and DL type of impact device) and smaller than 50mm (G type of
impact device), the small support ring or the shaped support rings should
be chosen.
• The sample should have enough mass. Minimum thickness of sample should
conform to Table 3.
• For the sample with hardened layer on surface, the depth of hardened layer
should conform to Table 3.
• Coupling. Light-weight sample must be firmly coupled to a part with much
larger mass. Both coupled surface must be flat and smooth. The impact
direction must be vertical to the coupled surface. When the sample is a big
plate, or long rod, it can be deformed and become unstable, even though its
weight and thickness is within allowable ranges, and accordingly, the test value
may not be accurate. So the sample should be reinforced or supported at its
back.
• AVOID any object that has a strong Magnetic Force.
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