EFFECT OF TIME. 



303 



and the general, and with it the total, elongation being 

 again increased. 



The effect of time influence on the strain of compres- 

 sion specimens is shown on the diagram on Fig. 154. The 

 curves here shown represent the relation of stress and 

 strain for two specimens of soft copper tested by the 

 author. The two specimens were turned from the same 

 bar, and were of the same size, being about lin. in 

 diameter and l^in. in length. 



In the case of the first one , after each increment had been 

 applied, the specimen was allowed ample time to come to 



Stress Tons per square inch. 

 FIG. 154. THE AUTHOB'S TESTS OP Two COPPER COMPRESSION SPECIMENS. 



rest and take up its full amount of set, for the larger loads 

 this time in some cases amounted to 20 minutes. When 

 this had been done, and before a new load was applied, 

 the bar was taken out of the machine and both its length 

 and diameter at the two ends measured. From these 

 measurements it was possible to calculate the actual 

 stress on the specimen at each length. 



For the second bar the operations were precisely the 

 same, except so far as regards the time during which the 

 load was allowed to remain on the specimen. It is 

 impossible to apply the load in a testing machine with 



