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mvip@mitech-ndt.com
5.1.2 Coupling
The following requirements must be met for the coupling:
The contact surface of the sample and the surface of the base plate must be level, flat and ground
smooth.
The impact must be carried out perpendicular to the coupled surface.
Impact devices types
Minimum sample thickness for coupling
D, DC, DL, E
3mm
G
10mm
C
1mm
Coupling procedure:
Apply a thin layer of coupling paste to the
contact surface of the specimen.
Application of coupling paste.
Press the specimen firmly against the base
plate and spread the paste using circular
motions.
The coupling process has been carried out
properly if there is no longer any metallic contact
between the parts.
Rubbing both parts
Carry out the impact vertically on the
specimen.
The coupling ensures a rigid connection between
the two parts, the absence of surface stress on the
specimen and thus reliable test values.
Coupled specimen
Insufficiently coupled samples produce large variations of individual measurements, HL values which are
too high and the operation is characterized by a rattling noise upon impact of the test tip.
5.1.3 Surface curvature of the test piece
Make sure that the radius of curvature of the sample surfaces is not less than 30 mm.
The unit can only work properly when the impact body is in a particular position in the guide tube at the
time of impact on the test surface. In the standard position, the tip of the impact body is precisely at the
end of the tube.
Impact device types
Radius
Impact device type G
min
R
=50 mm
Impact device types D/DC, C and E
min
R
=30 mm
