32 



MR. J. MUIR ON THE RECOVERY OF IRON FROM OVERSTRAIN. 



second column under each heading in that table gives the extensometer readings for 

 a test performed immediately after that given in the preceding column. 



These figures show that an immediate re-application of the load has produced iia 

 each of the three cases less total elongation than the first application, in consequence 

 of the bar's gradual settlement into a cyclic state through successive loadings. After 

 the recovery has become fairly perfect, this considerable diminution in the total elonga- 

 tion obtained by a second application of the testing load does not occur. This was 

 clearly shown in the table on p. 29. In the present diagram Curve No. 6' (shown 

 dotted) was obtained immediately after No. 6, and it shows almost no change in the 

 total elongation produced. 



The tests made immediately after treatment at 45 C. are shown by columns 

 2 and 3 of the table above to have given slightly greater total elongations than 

 those obtained from the loadings performed immediately before warming. This is 

 perhaps contrary to what might have been expected, since increase of tempera- 

 ture has been shown to hasten recovery. But although the total elongations 

 are greater, the process of recovery really has been aided. This is shown by the fact 

 that distinctly smaller yieldings are obtained with low loads after the bar has been 

 heated to 45C. But though the bar is more perfectly elastic under low loads, under- 

 higher ones the yielding which occurs has not been decreased ; so that, as the specimen 

 is subjected to a gradually increasing load, there is a transition from more elastic 

 l>ehaviour to less, which is suggestive of a yield-point. 



To return again to Diagram No. IX., the specimen, after being warmed to 45 C. in 



