Krautkramer DynaPOCKET - The Hardness Testing Method

7-2 Issue 03, 04/2005 Krautkramer DynaPOCKET
7.1 The hardness testing method
In the following section, you will find some helpful in-
formation about the hardness testing method of the
DynaPOCKET.
The DynaPOCKET is an integrated instrument, con-
sisting of impact body, impact device and display unit.
The impact body has a tungsten-carbide ball as a
spherical test tip, and a permanent magnet for generat-
ing a voltage pulse. The impact device has a spring
drive for loading and impelling the impact body, and an
induction coil for detecting the magnet in the impact
body. In rebound hardness testing, the speed variation
due to the impact body’s collision with the workpiece
surface is measured.
To carry out the measruement, the impact energy is
set via the spring. The impact body located in the tube
of the impact device is impelled against the test sur-
face by means of the release button.
In this process, the impact body’s magnet induces a
voltage signal in the coil, with the amplitude of this
signal being proportional to the impact phase speed
(Ip). The impact causes a plastic deformation of the
material, and a permanent spherical indentation is cre-
The rebound hardness testing method The hardness testing method
ated in the surface. This plastic deformation brings
about a loss of energy of the impact body, and conse-
quently leads to a lower speed after the rebound phase
(Rp).
The hardness value is calculated from the ratio of
these two speeds and displayed as follows:
HL = 1000 Ip/Ap
please also refer to VDI reports no. 308 (1978).
The speed ratio is determined exactly at the time of the
impact/rebound using the special signal processing. The
speed ratio is therefore unaffected by the impact direc-
tion. As opposed to this, other rebound hardness testers
require that the impact direction be predefined in fixed
steps (effects of gravitation on the speed ratio) – which
is a considerable handicap with frequently changing test
positions.
H Note:
With DynaPOCKET, it is not necessary to specify the
impact direction.