STKKSS VXD I'KKMANKNT STKAIN. 



uniform tensile stress and the corresponding semiplastic 

 strain in the case of wrought iron and steel. 



The first series of experiments were made upon nine 

 bars of wrought iron of soft quality, each bar being 



10 



15 



55" 



30 



LOG. STRESS. 



Fio. 162. LOGARITHMIC DIAGRAM OF STRESS AMI STKUN. 



turned parallel. In order to avoid the effect of previous 

 loading on the extension, each bar of the set was subjected 

 to one load only, the load being allowed to remain on the 

 bar for 30 minutes before the extension was measured. 

 The nine pieces tested were cut from one bar, which 

 made it possible to combine the results in the form of a 

 single stress-strain diagram for the range of load employed. 

 This is shown in Fig. 161. 



Using Prof. Osborne Reynolds' method of logarithmic 

 plotting, it was found that by plotting the logarithms of 

 the strains, expressed as fractions of the original lengths, 

 as ordinates, and the logarithms of the corresponding real 

 stresses as abscissae, the line shown on Fig. 162 was 

 obtained. It will be seen that the points corresponding 

 to the various bars and loads all lie on a straight line, 

 whose equation has the general form 



log. / = log. C + k log. e 



where /is the real stress on the bar, 



,, e is the corresponding strain, which in this case, is 



an extension, and is equal to -, ; 



and C and k are constants depending upon the material 

 tested. 



