﻿1 6 POPPLEWELL, U nif or 7ft Stress and Permanent Strain. 



In addition to the above table IX. the accompanying 

 diagram, Fig. 3, has been prepared. This contains the 

 logarithmic plottings for all the specimens, the logarithms 

 of the strains as abscissae and the logarithms of the 

 corresponding stresses as ordinates. The zero line for 

 the strain logarithms is the same for all the cases, but the 

 zero lines for the stress logarithms has been placed at 

 various heights so as to separate the curves and prevent 

 confusion. 



Referring to the results as shewn by the general 

 Table and by the diagram, it will be seen that the 

 values of k y as shewn by the slope of the lines, vary 

 somewhat from the value obtained in the tension experi- 

 ments of Dr. Stanton, namely, 0*25, being in some 

 cases below this value and in others exceeding it. The 

 probable reasons for this were mentioned when referring 

 to the difficulties attending compression experiments 

 of this kind, and it may be regarded as probable 

 that, if plastic compression tests could be made on longer 

 bars with the loads applied quite centrally, results more 

 uniform and more nearly agreeing with the tension results 

 would be obtained. 



The values of the second constant C will be seen to 

 exceed those for the tension experiments both in the case 

 of the iron and the steel, the difference for the results of 

 the iron and the steel being about the same. 



A notable exception is to be found in bar 4. The 

 results in this case are abnormal both as regards k and C. 

 It will be seen that the specimen in this case was smaller 

 than I, 2, and 3, and was of a very different quality 

 of iron. Apart from these two facts it is difficult to 

 account for the discrepancy. 



A further point which is worth noting is that the 

 values of k are higher and those of C lower where the 



