﻿Stresses on the Elastic Properties of Iron and Steel. 423 



tbc elastic limit was found to be 32,000; taking p as 32,000 

 andp 8 as 12,540, the apparent and true stresses given in the 



same line have been calculated. This same procedure was 

 followed in constructing the entire table. It is seen that the 

 apparent maximum unit shear is generally less than the 

 snearing strength of the material, and that the true maximum 

 unit shear is generally greater than the shearing strength of 

 the material (here shearing strength means the elastic 

 strength as determined from torsion tests), higher values 

 being given for the ease where Poisson's ratio was taken as 1/3. 

 In only a few eases in the case of the solid rounds and the 

 thick tubing did the apparent maximum tension exceed the 

 tensile strength of the material (tensile strength meaning unit 

 tensile stress at the elastic limit in simple tension): the 

 number of cases where the true maximum tensile stresses, 

 for solid rounds and thick tubes, exceed the tensile strength 

 of the material is greater than the corresponding number for 

 the apparent stresses. In the case of the thin tubing, how- 

 ever, it is seen that in no case did the apparent maximum 

 unit stress or the true maximum unit stress in tension 

 reach the elastic strength of the material : but in the case 

 of maximum unit shear the true stre>s; j s are greater than 

 the elastic strength of the material (not true for apparent 

 maximum shear, except in one case). In general, it is 

 seen from this table that the formulas for true unit 

 stresses with Poisson's ratio as 1/3 give the highest values, 

 those with Poisson's ratio as 1/1 the next highest, and the 

 formula? for apparent stresses the lowest. This is shown 

 graphically for the carbon and nickel steel solid rounds 

 by tig. 7. 



The conclusion to be drawn from Table II. is that in the 

 design of parts subjected to combined stresses the true 

 shearing strength should be used. Mr. J. J. Guest, whose 

 investigation was referred to in the Preliminary Eeport, 

 arrived at the same conclusion as the result of his investi- 

 gations. The entire uniformity of the results as shown by 

 the thin tubing, where the effect of the combined stresses 

 can be more exactly determined, gives the confidence in 

 this conclusion, in spite of the tact that the maximum 

 tension is usually supposed to govern the design of parts 

 subjected to combined stresses. 



