218 TORSION TEST. 



where /, is the maximum shearing stress, and x has a value 

 somewhere between 16 and 12. 



120. Stress at the Elastic Limit. In the above test, the 

 elastic limit may be said to have been passed at a twisting 

 moment of 500 inch-pounds. The formula 



may be taken as being true up to the elastic limit. 

 Putting this in another form, we have 

 16. T 



/.I 



d* 



16 500 



3-1416 . (0-472) 3 

 = 24,300 Ib. per square inch, 

 = 10*82 tons per square inch. 



The maximum twisting moment was 1,348 inch-pounds 

 Owing to the fact which has already been referred to, 

 namely, that near the point of fracture for a ductile metal 

 the stress is nearly uniform over the section, the second 

 formula must be employed : 



from which 



12 . T 



12 . 1348 



3-1416 . (0-472) 3 

 = 49,000 Ib. per square inch. 

 = 21'85 tons per square inch. 



The shearing stress for the same metal, as obtained from 

 direct shearing tests, is about 22'40 tons per square inch. 

 There is, therefore, no very great difference between the 

 two results, thus showing that it is right to assume the 

 condition of uniformity of stress at the maximum twisting 

 moment. 



