I'll I LOSOPH 1C AL TRANSACTIONS. 



I. On the Recovery of Iron from Overstrain. 



By JAMES Mrm, R.Sc., Trinity College, Cambridge (1851 K.i-hihiiii,,, S, '>< 

 Ifesearch Scholar, Glasgow University). 



Communicated by Professor Ewixo, F.Il.X. 

 Received January 25, Read Fe!nr.y 9, 1899. 



IT has long l>een known that iron which has been overstrained in tension that is to 

 say strained l>eyond the yield-point so that it suffers a permanent stretch possesses 

 very different elastic properties from the same iron in its primitive condition. The 

 material is said to be " hardened " by stretching,* since the ultimate effect of such 

 treatment is to raise the elastic limit and reduce the ductility of the material. 



More recently, attention has l>een called to the fact that, primarily, the result of 

 tensile overstrain is to make iron assume a semi-plastic state, so that the elastic limit, 

 instead of l>eing raised by stretching, is first of all lowered, it may be to zero.t This 

 plasticity may be shown by applying a comparatively small load to a liar of iron or 

 steel which has just been overstrained by the application and removal of a large 

 stretching load. When the small load is put on, the bar will l>e found to elongate 

 further than it would had the material been in its primitive state ; and a slight 

 continued elongation a "creeping" may occur after the small load has lieen 

 applied. If this load l)e withdrawn, a quite appreciable permanent, or semi- 

 permanent, set will l)e found to have been produced ; a set which diminishes slightly. 



* Kwixu, " On Certain Effects of Stress," 'Proc. Roy. Soc.,' No. 205, 1880. The raising of the clastic 

 limit due to stretching seems to havo been first noted in 1865 by TM M.KS. See a translation of his paper 

 in tin- I'liil. Mag.' for September of that year. 



t B.U's< 'inxiiKR, " Ueber die Veriinderung der Elasticitatsgrenze," ' Civilingenieur," 1881, or 

 " Mittlicilungen aits dem mechanisch-technischen Laboratorium der K. Polytechnischen Schulc in 

 Miinrhcn." An account of BAfscniMiKit's work is given in Uxwix's book on "Testing of Materials 

 of Construction." 



Kwixci, "On Measurements of Small St ruins in the Testing of Materials and Structures," 'Proc. Roy. S .<-.,' 

 vol. 5K, April, ls<>5. 



vol.. , \riii. A. B 31.7.P9 



