﻿6 POPPLEWELL, Uniform Stress and Permanent Strain. 



From this the stress 



W W.T W, 

 p=— = -=—U- e \ 



r a a . I a x ' 



In the present experiments, for each load imposed the 

 observed quantities were the load in tons and the 

 shortening of the specimen, and from this latter the- 

 permanent strain e was calculated. The initial area a 

 was already known, so that the actual stress was easily 

 calculated from the above expression. In all the results 

 given the calculations were made in this way, the shorten- 

 ing being determined in some cases by end measurements 

 only, and in others by both end and surface measurements. 



In the following tables are given the main results for 

 the eight specimens tested. Four of these bars were of 

 average wrought-iron, and the remaining four were of mild 

 steel. On each of the eight tables the results given are, 

 besides the initial dimensions, the loads imposed W. the 

 corresponding stresses /, the strains e, and the two 

 constants occurring in the fundamental equation. These 

 two last were found by plotting the logarithms of the 

 strains as abscissae and the logarithms of the correspond- 

 ing stresses as ordinates ; the points so obtained were 

 found to lie on a straight line whose slope gave the value 

 of the index constant k. The only remaining unknown 

 in the equation for each load was the second constant C 

 which was separately calculated for each load. 



