lO' X 40 



30 



20 



10 



0.10 0.20 0.30 



Octahedrol Sheortng Strom y 



0.40 



145 



- 40 X 10' 



30 



20 



10 



0.50 



Figure 1 - Octahedral Shearing Stress-Strain Curve Based on 

 Combined-Stress Tests of Ten Hollow Tubular Specimens 



on/ffj is the ratio of the tangential to longitudinal stress and is a constant during the 

 testing of a given specimen. 



The two curves are identical and are separated to avoid overcrowding the plotted points. 



Since all of these data, including those for a tube under pure ten- 

 sion, fall on this curve, it follov;s that the curve can be established from a 

 simple tensile test of a conventional test specimen. Once the r-y curve has 

 been established from such a coupon test, calculations can be made of the 

 energy absorption for some other type of stress distribution, as for example 

 that resulting from the loading of a steel diaphragm under hydrostatic pres- 

 sure. A description of such energy calculations in terms of the octahedral 

 variables is now given. 



For the general case of triaxial stress the energy AE absorbed per 

 unit volume (5) is given in terms of the true principal stresses and the nat- 

 ural principal strains as follows: 



Rules (b) and (c) for plastic flow state that 



«1 + «2 + «3 



:8] 



2] 



