SOLDERLESS WRAPPED CONNECTIONS 



PART II 



585 



tion in such a way that the mechanical strength and conductivity are 

 maintained unchanged with time. 

 In summary it has been shown that 



1. The connections are sufficiently intimate to permit solid state 

 diffusion but the strains are not high enough to cause cold welding of the 

 connection. 



2. The hoop stress relaxes as a function of time and temperature 

 according to well known activation energy equations with an activation 

 energy for copper wires on nickel silver connections varying from 12.5 to 



24 



20' 



12 



1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 



RATIO OF RELAXED HOOP STRESS TO INITIAL HOOP STRESS 



Fig. 23 — Stripping force plotted as a function of stress relaxation. 



40 kilocalories. It requires about 2500 years to relax half the hoop stress 

 at 77°F (25°C) and 40 years at 135°F. 



3. The twin processes of stress relaxation and self diffusion occur in 

 such a way as to maintain or increase the strength of the connection and 

 to leave the resistivity of the connection unchanged with time. 



4. The conclusion from all of these tests is that the life span of the 

 solderless wrapped connection appears to be ample for meeting any of 

 the likely requirements. This conclusion is reinforced by life tests of a 

 large number of wrapped solderless connections in service that have been 

 carried out over two years without a failure and by the long and satis- 

 factory tests of the screw connection whose success also depends on the 

 stress relaxation, diffusion processes. Such connections have been shown 

 to be satisfactory over periods of time in excess of twenty years. 



