SHEARING TESTS. 



98. Shackles for Holding Shearing Specimens. 



Shruring specimens may be either round or square or flat. 

 A very convenient form of shackle for holding round turned 



FIG. 77. 



specimens is shown in Fig. 77. Here the specimen to be 

 tested in shear is marked A. The specimen in this case 

 is a round one, and is turned so as to fit the shackles 

 accurately. The shackles themselves are B B and C. Of 

 these C fits the middle portion of the bar, and is attached 

 to one of the tension shackles of the testing machine, so as 

 to be pulled in the direction shown by the arrow ; the 

 two outer portions of the piece are held in the other 

 shackle, marked B. This is attached to the other 

 tension shackle, so that it can be pulled in the opposite 

 direction from that of the first. In shackles of this form 

 it is most important that the bar be fitted tightly into the 

 holders, so that it cannot possibly be bent and caused to 

 fail in that way. The reliability of the results of a shearing 

 test depend, to a great extent, on the manner in which 

 the test piece is gripped. It is usual in this arrangement 

 of a shearing test to slightly nick the bar in the parts 

 where failure may be expected to take place. These 

 grooves are shown on the figure. The holders themselves 

 must be of hardened steel. 



In one form the cutting edge of the middle holder is 

 adjustable on a spherical joint, so that the pressures on its 

 two edges may be equal. 



This form of shearing tackle gives good results for the 

 more ductile metals, but where cast iron is to be dealt with 

 a modified form must be employed, as there is too great a 



