Stress Systems in the Solderless Wrapped 

 Connection and Their Permanence 



By W. P. MASON and O. L. ANDERSON 



(Manuscript r(u-(>iv('(l Dcccinhcr 16, 1953) 



The solderless wrapped connection is initialhj held together by the hoop 

 stress in the wire which enters the connection as a result of the tension put 

 on the wire by the wrapping tool. Measurements made out to a time of l.o 

 years at room temperature show that the tension has decreased to 70 per cent 

 of the one day value (8000 lbs per square inch) in this period. Two methods 

 of extrapolation are discussed, both of which indicate that at least half of the 

 initial one day value will remain at the end of forty years at room tempera- 

 ture. 



Another set of stresses enters the connection as a function of time, namely 

 the dijfu.'iion forces produced by diffusion of the tin plating into the brass 

 terminal and copper ivire. A number of experiments are discussed which 

 show that the activation energy of diffusion is materially reduced by the 

 shearing stresses in the connection. Measurements at two temperatures, 

 which allow extrapolation to room temperature, indicaij that at the end of 

 two years the force required to strip the wire from the terminal has increased 

 by 5 per cent over the initial value and that at the end of forty years the 

 increase will be 20 per cent. Support for these conclusions is furnished by 

 tests on actual connections that have been in the field for one year and ten 

 months, which show an increase of 5 per cent in the stripping force even 

 though the relaxed hoop stress is only 68 per cent of the initial value. The 

 increase, which is due to diffusion forces, can be made higher by using zinc, 

 cadmium or aluminum plating, and the fusion occurs in a shorter time. 



IXTRODUCTIOX 



As discussed in a series of papers/ the solderless wrapped connection 

 is an efficient and inexpensive method of connecting a wire to a terminal. 

 All the tests made so far indicate that it is mechanically sound and 

 sufficiently free from the effects of corrosion to have a trouble free life 

 of at least forty years. Photoelastic and stress studies show that the 



» The Solderless Wrapped Connection, B. S. T. .]., 32, May 1953. 



1093 



