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X. Ductile Materials under Combined Stress. By 

 Walter A. Scoble, A.R.C.Sc, B.Sc, Whitworth Scholar*. 



[Plate I.] 

 Introduction. 



ri^HE theory o£ combined stress, and the results recorded 

 JL by earlier writers, were discussed in a previous com- 

 munication f, and the literature of this subject has since been 

 very fully reviewed, from an engineering standpoint, by 

 Mr. h, B. Turner % and Mr. C. A. Smith §. The most im- 

 portant experimental results obtained by other observers are 

 given later. 



The object of this paper is to further consider the results 

 of the writer's earlier experiments, and to record the data 

 which were obtained from some later tests made on tubes. 

 The results are also compared with those obtained by other 

 observers, who employed different methods and combinations 

 of loading. 



Further Consideration of the Earlier Tests. 



Specimens and Apparatus. — The first test bars were of 

 steel, | inch diameter, and 36 inches long. The ends were 

 of square section, f inch side, to allow a torque to be applied 

 to the bar. One squared end was held in a special clamp 

 which prevented this end of the bar from rotating under the 

 torque, but allowed it to take its natural slope as a supported 

 beam under a bending load. The bar was also supported, at 

 30 inches from the centre of the clamp, on V rollers, which 

 formed the other support under the bending load, and offered 

 no resistance to the torsion of the bar. A bar was bent as a 

 beam 30 inches long, supported at its ends, by a dead load 

 directly applied midway between the supports ; it was twisted 

 by means of a wooden pulley which fitted on the other squared 

 end of the bar. Two flexible wire ropes were attached to the 

 pulley, and exerted a couple upon it because of the weights 

 which they were made to carry. 



Therefore it will be noticed that when a bar was twisted, 

 it was subjected to a uniform torque all along its length, but 

 the maximum bending moment acted on one section only of 

 the bar. Within the elastic limit of the metal, the shear 

 stress produced by the torque varied from zero at the axis of 

 the bar, to a maximum all over the surface. Similarly the 



* Communicated by the Physical Society : read November 26, 1909. 

 f Proc. Phys. Soc. London, vol. xx., and Phil. Mag. Dec. 190'/>. 

 % Engineering, Feb. 5, 1909. § Engineering, Aug. 20, 1909. 



