SOLDERLESS WRAPPED CONNECTIONS — PART I 541 



within the yield point. Two springs, one of nickel silver wire and the 

 other of copper wire having a stiffness ratio of 5 to 6, were coupled in 

 series (Fig. 18), tensioned to 30 grams and then heated to 173°C for two 

 hours. The tension left after heating was 13 grams or 43 per cent of the 

 original tension. The tension decay curve was similar to that shown for 

 the wrapped connection. (See Fig. 17.) This test shows that in spite of 

 the complex deformation of the wire at the corners of the terminal 

 there is substantial agreement in results of the measurements ob- 

 tained — namely 43 per cent remaining stress in the case of the helical 

 spring and 47 per cent for the wrapped connection. 



STRESSES IN THE FINISHED CONNECTION 



Having determined the interacting forces in the solderless wrapped 

 connection, the next questions of primary interest are — what are the 

 stresses in various parts of the connection and what will happen to these 

 stresses in forty years? 



Most of the elastic energy stored in the wire is in the portion marked 

 ''Medium Tension" (Fig. 4). Here the stress is about 8,500 P.S.I. This 

 assumes that a 20-mil wire is wrapped with 1300 grams applied force. 

 The wrapped force or the useful force obtained from the elastic reserve 

 is then 1210 grams. 



The stresses at the corners are not easily determined because they are 

 not uniform. This is shown in Fig. 5. As can be seen, the point of highest 



A 



'A 



B 



NICKEL SILVER COPPER 



_-A,— >)^--ai— >K li > 





|<— 100%— 1— 



' T, = 30 GM 



untensioned'I 



BEFORE 

 yy , HEATING 



TENSIONED 



xk 



TENSIONED 



NTENSIONED 



AFTER 

 HEATING 



|wvvwvw\4aaa/^«/vv\a/VvV|aavwvv\/^ 



D ^VWVWWWVJAf I JMAMAjWWWvVWp " 



__^ |<— ELASTIC RESERVE 43% 



Fig. 18 — Tension Ti in coupled springs after heating for two hours at 173°C 

 is about 43 per cent of the original tension Tx- (Tension Tx approximately 10 per 

 cent below the yield point). 





