1104 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



The previous results show that the effect of temperature above room 

 temperature ou the solderless wrapped connection is to promote fusion 

 which brings an additional set of forces into the picture with regard to 

 the mechanical stability of the connection. In order to determine the 

 effect of fusion at room temperature, it is necessary to evaluate the 

 activation energy of diffusion. This is done by calculating the value H 

 in the simple rate equation 



r = To exp {H/kT) 



so that a given change of temperature corresponds to a given change of 

 time on the fusion force curve. If we compare the 175°C curve with the 

 100°C curve of Fig. 9, an activation energy curve as a function of residual 

 hoop stress is obtained as showm by Fig. 10. The value of stress is deter- 

 mined b}'- the average time values used in the calculation of the activa- 

 tion energy. It is shown that the activation energy for diffusion of tinned 

 copper on nickel silver in the presence of stress is in the order of 20 to 24 

 kilocalories per mole while that with no stress is in the order of 41 kilo- 

 calories per mole. It appears that higher stresses lower the activation 

 energy of diffusion just as they lower the activation energy for creep 

 and stress relaxation. Very high stresses can reduce the activation energy 

 to a value approaching zero which is the case of cold welding. The fusion 

 occurring in the case of the solderless wrapped connection is different 

 from cold welding in that it takes a finite time to develop any fusion 

 forces. 



From the activation energy values of Fig. 10, it is possible to predict 

 the rate at which the wrapped wire connection increases its strength at 

 room temperature. Such a calculation applied to the case of tinned 

 copper wire on a nickel silver terminal is given in Fig. 5 where it is shown 



10'' \0^ 10^ 10' 



TIME IN SECONDS 



Fig. 9 — Shearing strength of copper-tin-nickel silver connections as a function 

 of time and temperature. 



