smart technologies for safety engineering

Dynamic Load Monitoring 111
system (6) embedded in the frame. The mass is impacting on to the pneumatic cylinder via
a rubber bumper (7).
The data acquisition system included all necessary conditioning systems and amplifiers, and
served to acquire real-time measurements of all significant signals:
force signal from the piezoelectric sensor (8) fixed to the piston rod of the pneumatic cylinder,
in order to measure the actual impact history;
signal from the optical switch (9), which acts as a trigger and allows the vertical velocity of
the impacting mass to be determined just before the impact;
deceleration of the falling mass (10a);
acceleration (10b) of the piston rod of the pneumatic cylinder;
pressure in the cylinder, measured with a fast pressure sensor (11);
displacement of the piston by a linear variable differential transducer (LVDT) sensor (12).
The drop test stand enables a wide variety of impact scenarios to be simulated, defined by the
mass and the velocity of the impacting body in the instant of impact. The used mass range was
7.2–50 kg, while the impact velocity was dependent on the drop height, which was confined
to the range 0–0.5 m. Three different examples of direct measurements of impact forces are
presented in Figure 4.5. The kinetic impact energy in all three scenarios was approximately
30 N m.
In all observed impact phenomena it is possible to distinguish between two phases of the
process, as shown in Figure 4.5. The first phase (phase A) is characterized by rebounds between
the falling mass and the piston. The number of rebounds, the characteristic successive
reduction of the amplitudes and the time intervals are similar for the whole range of initial
conditions (mass and velocity) used in the experiment. The total duration of the first impact
Figure 4.5 Impact force measurements, examples: (left) drop height 40 cm, mass 7.2 kg; (middle) drop
height 25 cm, mass 12.2 kg; (right) drop height 15 cm, mass 22.2 kg. A, first impact phase; B, second
impact phase