When the twisting moment is applied, the torque is reacted by a torque shaft, which moves in
relation to the deflection arm. The movement of the deflection arm is measured by a linear
potentiometer, which is connected to a calibrated TQ digital torque meter to give a readout of the
torque in a unit of Nm or lb.in. The more we turn the input handwheel clockwise to increase the
degree of rotation, the more torque is produced. At the initial stage, the graphical relationship of the
torque and degree of rotation measured is linear as demonstrated in figure 5. The specimen is elastically deformed and the recovery of the specimen to its original shape is possible if the specimen
is unloaded. However, if a high degree of rotation is applied passing a proportional limit, the
specimen starts to deform plastically and will not return to its original shape when the input
handwheel is turned anti-clockwise.