APPARATUS FOR MEASURING STRAIN AND APPLYING STRESS. 



285 



X. — Effect of Torsion on Tension. 



The effect of torsion upon the properties of a bar subjected to tensional stress was 

 only examined below the elastic limit. 



The measuring instrument used was of the Ewing type,* each unit of extension 

 representing 50 o o inch upon an 8 -inch length ; diameter of bar, 0*498 inch. 



A series of tests were made, beginning with no tension and increasing by equal in- 

 crements until the yield-point of the material was reached. The results are recorded in 

 Table IX., and it will be seen that no difference was observable, whether the bar was 

 twisted or not, provided the elasticity of the bar remained unimpaired. 



Table IX. 





No Torsion. 



Torque of 141 inch lbs. 



Torque of 282 inch lbs. 



Torque of 423 inch lbs. 



Loads. 

 ' Lbs. 





















Reading. A 



Reading. A 



Reading. A 



Reading. A 



200 





















15 



15 



16 



15 



400 



15 



15 



16 



15 





14 



15 



15 



16 



600 



29 



30 



31 



31 





14 



14 



15 



14 



800 



43 



44 



46 



45 





16 



15 



15 



15 



1000 



59 



59 



61 



60 





14 



15 



14 



15 



1200 



73 



74 



75 



75 





14 



15 



14 



15 



1400 



87 



89 



89 



90 





15 - 



14 



14 



14 



1600 



102 



103 



103 



104 





14 



15 



14 



14 



1800 



116 



118 



117 



118 





15 



15 



14 



16 



2000 



131 



133 



131 



134 





15 



14 



15 



13 



2200 



146 



147 



146 



147 





15 



14 



14 



15 



2400 



161 



161 



160 



162 



XL — Effect of Bending on Torsion. 



One of the most interesting cases of stress which occurs in practice is that of torsion 

 combined with bending, a subject which has received little or no attention from the 

 experimental side. The apparatus described in Section II. enables uniform twist and 

 uniform bending to be applied to a bar in any proportions, and the torsional strain to be 

 accurately measured without reference to any external body ; so that the bar can 



* On Measurements of Small Strains in the Testing of Materials and Structures. By J. A. Ewing, F.R.S. Proc. 

 Royal Society, May 1895. 



