Solderless Wrapped Connections 



PART II — NECESSARY CONDITIONS FOR OB- 

 TAINING A PERMANENT CONNECTION 



By W. P. MASON and T. F. OSMER 



(Manuscript received February 9, 1953) 



In order to study the stresses and strains occurring in a solderless wrapped 

 connection, a photoelastic technique using photoelastic hakelite and a photo- 

 plastic technique using polyethylene have been used. Polyethylene has a 

 stress strain curve similar to a metal and can he used to investigate strains 

 in the plastic region. Using these techniques, it is shown that the connec- 

 tion is held together hy the hoop stress in the wrapping wire. In order to 

 lock this in, a dissymmetry from a circular form has to occur. This may he 

 in the direction of an oval shape or a square or rectangular shape. Sharp 

 corners are preferred since a more definite contact area results. A num- 

 ber of rules are derived for constructing the most satisfactory solderless 

 wrapped connection. 



It is shown that the connection between the wire and terminal is intimate 

 enough to permit solid state diffusion, but the strains are not high enough 

 to cause cold welding of the connection. The life of the joint depends on the 

 twin processes of s'ress relaxation and self diffusion. Stress relaxation 

 occurs at a rate such that half the hoop stress is relaxed in 2500 years at 

 room temperature. This loss of stress is compensated by the diffusion of 

 one part of the joint into the other. Since the activation energies for stress 

 relaxation and self diffusion are approximately equal for most metals, the 

 two effects complement each other and produce a connection which should 

 remain unchanged for times in excess of forty years under any likely 

 ambient conditions. 



INTRODUCTION 



The solderless wrapped connection described in the paper by R. F. 

 Mallina (see page 525) provides a very satisfactory and economical 

 method for making connections with apparatus terminals when such 



557 



