Development and manufacturing of non-
destructive testing equipment and system
Hardness tester NOVOTEST T-UD2
generating a voltage pulse; the impact device has a spring
mechanism for loading and impelling the impact body, and an
induction coil for detecting the magnet in the impact body. In the
rebound hardness testing method, the speed variation caused by
the impact of the impact body against the material surface is
measured.
The impact energy is adjusted via the spring for the measurement.
The impact body contained in the tube of the impact device is
impelled against the test surface by means of the release button. In
the course of this, the magnet of the impact body induces in the coil
a voltage signal whose height is proportional to the impact phase
speed. The impact causes a plastic deformation of the material and
a permanent spherical indentation is produced in the surface. This
plastic deformation leads to a loss of energy of the impact body and
thus to a lower speed after the actual rebound phase.
The speed ratio is determined exactly at the moment of
impact/rebound by means of the special signal processing. The
speed ratio is therefore unaffected by the impact direction. As
opposed to this, other rebound hardness testers require presetting
of the impact direction in fixed steps (influence of gravitation on the
speed ratio) - which constitutes a considerable disadvantage with
frequently changing test positions.
5.2. UCI method
The Vickers diamond is fixed to the tip of a round metal rod. This
metal rod is excited, to its resonant frequency of approx. 78 kHz,
into longitudinal oscillations. When the Vickers diamond contacts the
sample surface, the resonant frequency will change. This change
happens in relation to the size of the indent area from the Vickers
diamond. The size, in turn, is a measure for the hardness of the
tested material. Resonant frequencies can be measured very
accurately. This is why the UCI method is suited to make the
