Mr. T. E. Stanton on 



Experiments on the Relation between Uniform Stress 

 and Permanent Strain in Wrought-iron and Steel. 

 By T. E. Stanton, B.Sc, Demonstrator in the Whit- 

 worth Engineering Laboratory, Owens College, 

 Manchester. Communicated by Professor Osborne 

 Reynolds, F.R.S. 



(Received October 21st, 1893.) 



When an iron bar is subjected to uniform longitudinal 

 stress exceeding its elastic limit, the connection between 

 the stress and the permanent set of the material is 

 usually shown by means of a Stress-Strain diagram, in 

 which the stresses are represented by the ordinates, and the 

 corresponding elongations by the abscissae of the curve. 

 These can be traced by an autographic apparatus attached 

 to the machine, several types of which are in use. 



The objection to this method is, that the position of the 

 curve, and also its form, are greatly influenced by the rate 

 at which the load on the bar is increased. Prof. Ewing* has 

 also shown that the effect of a pause in the loading has a 

 hardening effect on the bar, which increases with the length 

 of the time during which the load is kept constant. On 

 increasing the load after this interval, it is found that 

 permanent set does not again take place until a considerable 

 increase in the load has been made. This has been called 

 the " hardening effect of the time." 



An illustration of this is shown in Fig. 1, which is the 

 Stress-Strain diagram for a wrought-iron bar tested in the 

 following manner : — 



The bar was turned accurately parallel and fixed in the 

 Testing Machine and a stress of 16 tons per square inch of 



Ency. Britt., "Strength of Materials," 30-33. 



