Manchester Memoirs, Vol. xliii. (1899), No. 10. 



X. Experiments on the Relation between Uniform 

 Stress and Permanent Strain in Annealed Copper 

 Bars and Wires. 



By George Wilson, M.Sc. 



Demonstrator in the Whitworth Engineering Laboratory, 

 Owens College, Manchester. 



Received and read Match 21st, i8gg. 



The relation existing between the permanent set in 

 an iron bar and the uniform longitudinal stress inducing 

 it has been demonstrated experimentally by Dr. T. E. 

 Stanton in a previous communication to this Society,* 

 wherein it is shown that the stress varies as the fourth 

 root of the strain. 



The extension of these experiments, using annealed 

 copper bars as described below, brings out the fact that in 

 this case the stress, instead of varying as the fourth root, 

 varies approximately as the square root of the strain, 

 the index altering slightly according to the method of 

 straining the bar. 



In the experiments made by Dr. Stanton, each bar 

 operated upon was rapidly subjected to a pre-arranged 

 load. It was then allowed to stand under this load for a 

 period of thirty minutes, after which it was removed from 

 the machine and the diameter and extension measured. 



Thus, by straining a sufficient number of bars, it was 

 possible to obtain a series of points on the stress-strain 

 curve. If, instead of the stresses and strains, the logarithms 

 of these quantities are plotted, according to the method of 



* Manchester Memoirs, vol. viii., 1893-4. 

 September 8th, i8gg. 



