430 MR ANGUS R. FULTON ON EXPERIMENTS TO SHOW 
lower modulus of elasticity of the pair may show the higher strength factor. Before 
proceeding, then, to determine extreme fibre stresses by the ordinary formula, an attempt 
has been made by modifying it to connect up the stresses induced at the point of 
ultimate fracture in cross-breaking with the ultimate stresses in direct compression, 
tension, and shear. 
0) i 
a 
IY 
= sO. 
YY 
The probable development of the stress diagram of a beam of rectangular section, 
supported at two ends and loaded in the middle, is shown in fig. 38 for the typical case 
of an Ash beam. O,N,T;, is the stress diagram up to the elastic yield-point C, of the 
extreme fibres on the compression side. During the second period elastic yield con- 
tinues on the tension side until the extreme fibres on that side also reach the elastic 
limit T,. Meanwhile, since the compression strain of the extreme fibres on the other 
side has been mostly plastic, the compression stress has not increased proportionately 
