Other devices use both compression and tension, and comprise so-called ‘universal
tension and compression’ apparatus (Instron; overload dynamics). Their main advantage
is the accuracy with which the different materials can be subjected to the different tests
known in the field of feed and food engineering. These devices consist of a fixed plate
containing a load cell and a moving bar with variable speed. On this instrument
measuring bodies of a various geometry (either knife or plate for example) can be fitted
and uniaxial compression, uniaxial tension, three-point bending and cutting experiments,
respectively, can be performed (Luyten et al., 1992). For the testing of pellets, uniaxial
testing (plate) and cutting (knife) experiments are most appropriate. The force units
needed to break the pellet (or a series of pellets) is recorded as a function of time. Both
single (see example Fig. 5, plate) and multiple sample pellet(s) can be tested.