484 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 



QJ 5000 



'-' 3000 



5 2000 



0.6 0.8 1.0 1.2 1.4 



AMPLITUDE OF MOTION IN MIL-INCHES 



Fig. 11 — Total wear for one billion cycles plotted against the length of stroke 

 for two normal loads. 



wear curve obtained for A phenolic (a paper filled phenolic) plotted as 

 a function of the number of cycles. This wear was obtained by drawing 

 a 0.025-inch nickel silver wire for a distance of 2.0 mil inches over the 

 surface of the bar. The bar was \ inch wide. The normal force used was 

 30 grams (0.0665 pound). The wear was measured from the depth cut 

 in the material and from this since the wire was round, the total volume 

 of wear in cubic mil inches could be calculated. The rate of wear was 

 faster at the start but approached a limiting rate mth a large number of 

 cycles. 



A number of different lengths of stroke were employed and for the 

 A phenolic the total wear for a billion operations is shown plotted by 

 Fig. 11. The wear is approximately proportional to the slide but ex- 

 trapolating down to small motions it appears that there is a threshold 

 of motion below which the wear is very small. The values indicated are 

 close to the no gross slide regions found from the force curves of Fig. 

 9 for both forces shown in Fig. 11. To check that the wear was definitely 

 less in the no gross slide region an amplitude of motion of 0.075 mil 

 inch for a normal force of 50 grams (0.11 pound) was run for a billion 

 operations. The wear observed was so small that it could not be measured 

 quantitatively, confirming the lower rate of wear in the elastic region. 



