SOLDERLESS WRAPPED CONNECTIONS — PART H 



573 



load, cooling under a load, and then removing the load at room tem- 

 perature. Fig. 15 shows the loading and unloading curves for poly- 

 ethylene as a function of temperature. The stress required to produce a 

 given strain decreases very rapidly as the temperature increases, al- 

 though the recovery remains about the same irrespective of the tem- 

 perature. Suppose now that we apply a load and cool the polyethylene 

 down to room temperature maintaining the strain. When the weight 

 is taken off, the unloading curve will parallel that of the 20°C curve, 

 and 42 per cent recovery will be obtained at 50°C and 12 per cent for 

 90°C. 



In order to see if a wrapped joint would be simulated by this means, 

 a one-quarter inch rod of polyethylene was heated up to 97°C, was 

 wound with a one pound winding weight and was cooled to room tem- 

 perature with the weight attached. This was sufficient to prevent the 

 ''wire" from unwrapping and when the weight was removed, the poly- 

 ethylene "wire" gripped the metal closely and formed a bond similar 

 to the wrapped connection. In order to analyze the strain, one has to 

 cut a section through the center of the wire and put the section in the 

 polariscope. First, a number of unstrained polyethylene samples were 

 cut by various techniques and it was found that if they were cut with a 



0.02 



0.04 



0.12 



0.06 0.08 0.10 



STRAIN IN PER CENT 



Fig. 15 — Stress strain recovery curves for quenched polyethylene. 



0.14 



