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BELL SYSTEM TECHNICAL JOURNAL 



stiffen up more rapidly with compressional displacement than will a 

 contact made on a single hill. This concept of a loose contact, 

 therefore, seemed to offer possibilities in the way of an adequate ex- 

 planation of the experimental results. 



At first the problem seemed too complex for mathematical analysis 

 and a study of the elastic behavior of contact surfaces having various 

 arrangements of little hemispherical hills was made with the aid of 

 large scale rubber models. Quarter inch rubber balls were cut in 

 half for this purpose and arranged on bases of suitable material and 

 shape. 



0.001 



0.05 



0.1 



0.005 0.01 



DISPLACEMENT IN CENTIMETERS 



Fig. 24 — Stress-strain characteristics obtained with contact surfaces made of rubber. 



In Fig. 24 we have plotted the force-displacement characteristics 

 of three different surfaces: /, that of a single smooth hemisphere; 

 //, that of small hemispheres of equal height evenly distributed on a 

 portion of a large 32 inch sphere made also with rubber; and ///, 



