CHAPTER V. 



TESTING OPERATIONS. (Continued.) 

 SHEARING AND BENDING TESTS. 



97. Shearing Tests. There are feAver tests in compression 

 than in tension, and there are still fewer in shear. The 

 reason for this is not far to seek. Shearing tests are not 

 so easy to carry out satisfactorily as are tension tests, 

 strain measurements are difficult to make, and, more- 

 over, these tests yield no results beyond the ultimate 

 shearing stress. If the tensile properties of a metal are 

 known, or can be ascertained, it is sufficient for all prac- 

 tical purposes to assume the shearing strength to bear a 

 definite ratio to the tensile strength, as it has been deter- 

 mined that this shearing strength does depend on the 

 tensile strength in a fairly constant ratio for a given 

 metal. What has here been said relates only to direct 

 shearing tests where the conditions that obtain are similar 

 to those in a riveted joint. Shearing takes place in a 

 bending test, but the most satisfactory way of investigating 

 the shearing properties of a material is by subjecting it to 

 a test under a torsional stress, where there is shear taking 

 place in a circular direction. 



A reference to Fig. o (p. 16) will make clear the condi- 

 tions under which a shearing test is to be carried out. If the 

 bar to be tested is A B, the portion A must be rigidly held 

 while the other part B is also held in a similar way ; but 

 these two portions, A and B, are to be moved in opposite 

 directions. It is extremely important that the two holders 

 or shackles shall be placed very close together, so that 

 there is no tendency to bending in the portion between 

 the two in which the shear takes place. This is effected 

 by having the two shackles placed very near to one 

 another, and by making them to. fit the bar accurately and 

 tightly, so that there is no play or freedom to yield. In 

 some shearing tests, single shear, as depicted in Fig. 5, 

 is made use of. It has, however, been found much more 

 convenient to apply the load in double shear ; that is to 

 say, to have the two end portions of a bar held, and to 

 shear away the middle portion. 



