As reported by Field and Waters [25], a significant fretting damage can occur when the nominal range of slip, S, is between
8 and 14 lm according to Eq. (3.1) [16,26]. Therefore the mean pad span, x, used in this work was designed to have a length
of 10 mm as shown in Fig. 4, in order to achieve the recommended nominal range of slip.
S ¼ rax=