MI: .1 MI n; UN TIIK i;i;c(ivi-:i;v <F ii;>N i'i;n\i U\T.I;STI;AIN. 



17 



rod of fairly mild steel. It gave an ultimate strength of about .'!'_' tons JMT sijuaie 

 inch, with an elongation () f 2G per cent, on an 8-inch length. The jirimarv vield- 

 jioint occun-ed at a stress of 48,000 Ibs., or about 2t tons JMT square inch. It will 

 IK- noticed from the table of figures that this material recovered very slowly, for even 

 after forty days" rest recovery \\as !.\- n.. nie:ms complete. S|M-.-]M,.-' ; A of th ftbovt 

 table \\as further tested after about three and a-half months, an<l considerable imjier- 

 fection of elasticity still found. 



Although the table given above shows close agreement U-tween the elastic state- of 

 the material in the two cases, there was really an interesting difference l*-t \\een them. 

 This is clearly shown by Diagram No. V. Curves A and B in that diagram illustrate 



Diagram No. V. (Recovery under stress.) 



pool**'* A * B,*min*. 



S3 -~*Z- 



Scale . / unit - 



Fig. A represents the elastic condition of an overstrained specimen, which li.nl ITCH 



resting for forty days at a stress of 55,000 II*. in -'. 



Fig. B represents the clastic condition of an overstrained specimen, which had Wen 

 resting for forty days free from stress. 



the testing of the two specimens after the forty days' rest referred to above ; the last 

 thirty of these days were uninterrupted by any intermediate testing, and during that 

 time A was in the testing machine, \\ith a load of 55,000 Ibs. per square inch ajiplied 

 to it. The extensomettr having been applied to A, the load was gradually removed, 



\,,i. exam. A u 



