SHEARING TESTS. 



165 



possibility of cross-breaking. The shearing test apparatus 

 shown in Fig. 78, as used by Professor Johnson, of Wash- 

 ington University, is suitable for all classes of metals. 

 Instead of the test piece being simply placed in position 

 in the shackes it is firmly bolted in place, as shown in the 

 illustration. The holding dies are made of hardened 

 steel. Both the middle and ends are fixed in this way. 

 The load is applied by placing the apparatus between the 

 two compression plates of a testing machine. There is no 

 reason why this should not be arranged so that the load is 

 applied from the tension shackles as before. The bar to 



Fig. 78.* 



be tested may be of the square form, as shown, or the dies 

 may be cut out in the form of semi-circular recesses to 

 take round bars. In this apparatus it will be seen that 

 there is no possibility of freedom or shake, and conse- 

 quently no tendency to cross-breaking. 



It is not usual Avhen using this apparatus to cut grooves 

 in the bars. 



The operation of carrying out a shearing test is fairly 

 simple in the case of the first piece of apparatus described ; 

 care must be taken that the test bar fits the holders 

 accurately and tightly, and also that the pull is quite 

 central and symmetrical. Before the test, the dimensions 

 of the bar must be carefully determined. In this case the 



*. Johnson's "Materials of Construction, " page 387. 



