﻿546 Mr. W. A. Scoble on the Strength and Behaviour 



being both tension and compression, either kind of additional 

 force would reduce the strength, causing the bending moment 

 to be less than the torque. This is contrary to the results 

 of the experiments, so that the idea must be abandoned. 



Fig. 6. 



\-fs^\ 



Unvvin gives the working tensile stresses as more than twice 

 the torsional shear stresses for nearly all materials, in certain 

 cases the proportion being exact, thus opposing the idea of 

 friction. Referring to Mr. Guest's results, friction would cause 

 the maximum shear stress at yield to diminish with increase 

 of tension, and anti-friction would have the reverse effect. 

 In the case of tube 1, the tension was greater than twice the 

 shear stress. With tubes 4, 6, 7, 8 and 9, the tension was less 

 than twice the shear stress. All these tubes were steel. 

 With the copper tubes the shear strength was more than 

 half. the tensile stress. The brass tubes gave no definite 

 evidence either way. The bulk of these results are contrarv 

 to the working stress proportion, and there is an exception 

 amongst them. To trace the matter more completely, the 

 results were analysed to trace the connexion between the 

 maximum shear and the tensile stress across the plane. It 

 was found that there was absolutely no connexion between 

 them. As an example, taking the twenty tests on tube 8, 

 the maximum shear stress and the tensile stress across the 

 plane have been tabulated : — 



Max. Shear. 



Tension-. 



Max. Shear. 



Tension. 



Max. Shear. 



Tension. 



23735 



22320 



21760 



20290 



20975 



19220 



23175 



22325 



21600 



19600 



20800 



19000 



22810 



21590 



21460 



20040 



20600 



20600 



22500 







21370 



19630 



20535 



18765 



22260 



20340 



21250 







20480 



18720 



22100 







21125 



17000 



20100 



20100 



22000 



13400 







20050 



18450 



