The fretting fatigue test was conducted using a steel ring assembly designed to exert and sustain a normal force needed to
create the clamping load, as shown in Fig. 3. Strain gauges were installed on the sides of the ring to measure any deformation
while a load is being exerted. The Wheatstone bridge circuit was used to compensate for any deformation change due to
temperature fluctuations or other environmental factors, although all experiments were carried out at constant room temperature.
The pressure created by the contact pads is then expected to induce fretting through the small relative displacements
from the applied cyclic loads. Each pad has two contact surfaces, as detailed in Fig. 4. The distance between two
contact surfaces was designed to be 10 mm. The pads were made of the same Böhler M200 steel.