MEASURING FORCES AND WEAR IN SWITCHING APPARATUS 493 



equals T and its value is found to be 



fN 



(18) 



The added slip increases the displacement bx and it is shown tiiat the 

 total displacement is equal to 



5« = 



3/A^ (2 - a) 

 16)ua 



1 - 1 - 



}N 



(19) 



A plot of this curve is shown by tlu^ line OPQ of Fig. 17 and it is evident 

 that the displacement before gross slip occurs is 1.5 times larger than 

 the elastic displacement calculated on the assumption of no slip. 



These calculations have been extended in a recent paper"* to include 

 the case of a cylically varying force T ^ jN and it is shown that the 

 force displacement curve is a hysteresis type loop whose end points lie 



TOTAL DISPLACEMENT 

 INCLUDING SLIP 



-0.8 -0.6 -0.4 -0.2 



3(2-cr)fN 

 PACTOR TIMES — 7^—^ 



0.2 0.4 0.6 0.8 



TO GIVE DISPLACEMENT 



Fig. 17 — Displacement versus force wiieu slip is introduced. Hysteresis curve 

 PRU shows displacement for an oscillating force. 



