1106 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



force confirming the data of Fig. 10 of Mallina's paper, referred to in 

 Footnote 2, which shows that the hoop stress decreases less rapidly 

 than the applied tension. Fig. 11 shows the strip off force as a function 

 of time and temperature. If we subtract the relaxed frictional force from 

 the stripping force and divide by the area of 0.0027 scjuare inches (60 

 per cent of the area of the usual connection) the shear strength curves 

 in pounds per square inch are shown by the lower solid curves. These 

 start sooner than the values on Fig. 9 but require a somewhat longer 

 time to reach their final value. The activation energy obtained from 

 these curves is plotted on Fig. 10 (4800 psi) and shows that the activa- 

 tion energy for the lowest stress is about the same as that for the higher 



X O 



I/) a. 



V'lg. 11 — Stripping force and shear strength of copper-tin-nickel silver connec- 

 tions as a function of time and temperature. Initial stress is 4,800 pounds per 

 square inch. 



stress curve, showing that the shear stress is independent of the wrapping 

 tension. It takes longer to complete the process and as a result, the strip- 

 ping force at the end of forty years is equal to the initial value rather 

 than 20 per cent higher as in the case for Fig. 5. Corrosion tests for these 

 lower stripping force values show, however, that there is no indication 

 of a loss of electrical contact. 



The method for analyzing fusion forces by subtracting relaxation 

 data from stripping force data is verified by measurements on other 

 metal connections. Fig. 12 shows the ratio of stripping force to intial 

 stripping force for aluminum on nickel silver terminals as a function of 

 time and temperature. Subtracting the relaxed force (the original strip- 

 ping force multiplied by the relaxed stress ratio of Fig. 4) from the strip- 

 ping force and dividing this difference by the contact area, the shearing 



* R. H. Van Horn, Solderless Wrapped Connections, Part III — Evaluation 

 and Performance Tests, B. S. T. J., 32, May 1953. See Table II. 



