216 TORSION TEST. 



The mean of these is 



176 

 175 

 179 

 1-80 

 1-84 

 1-84 

 1-86 

 1-86 



8)14-50 



i si on / degrees for each 225 inch-pounds 

 8 i ^ { of twisting moment. 



Making use of the formula already mentioned, on page 46, 

 the Modulus of Rigidity is 



r 5760 . I . T 



ir 2 . a. d* 



In the present case 



I = Sin. 



T = 225 inch-pounds. 

 TT = 3-1416 

 a = T8125 degrees 

 d = 0*472 in. diameter. 

 Putting in these values, 



5760 . 8 . 225 



G = 



(3-1416)* . 1-8125 . (0-472) 4 

 = 11, 800,000 Ibs. per square inch. 

 = 5,225 tons per square inch. 



The value of the modulus of direct elasticity for mild 

 steel is somewhere about 30,000,000 Ib. per square 

 inch ; in the example given on a former page it was found 

 to be 28,860,000 Ib. per square inch. It has been 

 shown (page 20) that, reasoning from purely theoretical con- 

 siderations, the ratio of the modulus of rigidity, G, to the 

 modulus of direct elasticity, E, is as 2 to 5, or 



J = ? = 0-400 

 E 5 



Now, taking the values found in the two cases quoted, 

 G = 11,800,000, and 

 E = 28,860,000, 

 So that the ratio 



G 11,800,000 _. 

 E " 28,860,000 



