Mi;. .1. Mill; <>N Tin. IM-PIVKKV OF IKON Ki:M (VKI;STI;AIN. 



Stress in tons por 

 square inch. 



Total l".i' I in t"- 



I-;\icn>iinetcr readings. 



'""it = nmnr 

 of an inafc. 







1 



I 



4 



6 



8 



10 



II 



14 



16 

 18 

 20 

 22 



21 

 



26 

 87 





 0-79 



l :..< 

 3-16 

 Sec. 



27J 



30 put on 







30 



60 30 



120 60 



180 60 



240 60 



;500 60 



360 60 



421 61 



481 60 



r,40 



600 K. . T. '- ifift 



660 60 , 



720 60 



750 30 



780 30 



810 30 



still 810 after 4 minutes, 

 but 830 6 



iVc. &c.(seeCurve No. 1, Diagram II.) 

 1595 after 20 minutes 

 1700 and then quickly out of range 

 gradually and kept on for 3 minutes, the beam of the testing machine remain- 

 ing steady 



These figures show that this specimen has accurately obeyed HOOKE'S law, until a 

 stress of -7 t>ns per square inch was attained. At this load the yield-point w;is 

 exjiected tn occur, and although the exteusometer reading obtained gave HO evidence 

 <>f the proximity of such a point, by simply allowing the load to remain on for a short 

 time (4 minutes) the creeping recorded above set in, or perhaps spread from without 

 to within the 8-inch length under test.* The yield-point, with this specimen, has. 

 therefore, coincided with the elastic limit as accurately as the extensometer can 

 measure. Usually, in testing, imperfection of elasticity is shown before the yield- 

 jMiint is reached, and if a load less than that at the yield-point be allowed to act for 

 some time, then a slight creeping probably supervenes. When, however, a l>ar, like 

 that referred to above, has shown very perfect elasticity up to the yield-point, it is 

 pr< 'liable that a load verv little under that at which the yield-point occurs could be 

 sustained for an indefinite time without creeping taking place. Even although 

 slight imjiertection of elasticity be shown before the yield-point, experiments showed 

 that no creeping need necessarily occur for a pause in the loading of at least a night's 

 duration. . 



k The fact tlmt yielding take* some time to start has already licen recorded by Professor Kwix<; in liis 

 piper ciu-d aUve, "On McaatirctmmU of Small Strains, \-c." (see pp. 135 and 130). He hiw noticed that 

 yielding may k-gin in ;i part of the Kir lying outside the 8-inch length to which the extensometer is 

 .ippliud. and may gradually sprr.nl .-ilcm^ tliu liar. 



