STRENGTH OF STEEL. 



377 



Cylindrical bars, K and L, of the same material as the 

 above. Seven different extensometers were used, with 

 the following results : 



TENSION MODULUS OF ELASTICITY OF STEEL BARS. 



200. Strength of Steel in Shear and Torsion. 



The ratio of the ultimate shearing strength of steel to 

 its strength in tension has already been referred to 

 (p. 167), and some results collected from various sources 

 are there given. Some of these are repeated in the following 

 table, with the addition of others. The ultimate shearing 

 strength, as calculated from the breaking moment in torsion 

 tests, is also quoted in some cases. Two values of this 

 coefficient of torsional strength have been calculated. The 

 first is calculated by the usual torsion formula, which 

 assumes elasticity up to the point of fracture, the formula 

 being 



- 2 T 



/T 7T R 3 



The second formula assumes equality of stress over the 

 cross section of the shaft at the point of fracture, and is 



3 T 



/T ~27r R s 



The results in the table show that the conditions 

 assumed in the second formula are those which actually 

 obtain, the coefficients being in most cases very near the 

 shearing strengths as obtained from direct shearing experi- 

 ments. The figures in brackets are not given by the 

 authorities named, but have been calculated by the author 

 from the published results. 



