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Fig. 8 — Diffusion shearing strength for tinned copper wire on nickel silver at 

 17o°C as a function of time. 



more, it appears that the fused bond will just withstand a shearing stress 

 equal to the limiting shearing stress of tin. Metallurgical evidence for 

 this diffusion was presented in Fig. 19 of the paper referred to in Foot- 

 note 4. In this figure, a tin plate layer between the copper and nickel 

 silver was diffused in the two metals in a time of about 400 hours at 

 180°C. The new evidence indicates that this layer of tin has the shear 

 strength of bulk tin. 



The previously described data constitutes measurements of fusion 

 forces separate from the complications of friction in the solderless 

 wrapped connection. However, the same measurements of the effect 

 of fusion are obtained if one subtracts from the stripping force the 

 product of the relaxed force times the initial stripping force (about 15.5 

 pounds) of the actual wrapped connections. As shown by Fig. fi, the 

 fusion force so computed divided by the area of contact of a six turn 

 connection (about 0.0045 sq in) yields the shearing stress, previously 

 defined. In Fig. 9, the shearing stress is given for a tinned copper wire 

 on a nickel silver terminal as a function of time for 17o°C and 100°C. 

 By way of comparison, the constant stress diffusion process of Fig. 8, 

 is shown plotted by the dashed line on this plot. It is evident that there 

 is a larger induction period in the case of the 14 gauge (0.005 inch wire) 

 than in the case of the smaller 24 gauge (0.020 inch) wire and the ratio 

 of the times is proportional to the scjuare of the wire diameter ratio. 

 This is an indication that we are dealing with a nucleation process. 



