PUNCHING TESTS. 



167 



TABLE OF SHEARING STRENGTH OF VARIOUS 



METALS. 



99. Punching Tests. These are analogous to shearing 

 tests ; in fact, punching is in reality shearing on a cylin- 

 drical instead of a plane surface. These tests may easily 

 be carried out in an ordinary testing machine which has 

 been arranged for compression tests. The only additional 

 apparatus required is shown on Fip-. 79. Here A is the 

 punch, made slightly tapering upwards, B is the plate to 

 be punched, and C is tne lower die or bolster, in which is 

 a conical hole D. The smaller diameter of this hole is 

 made slightly larger than the bottom diameter of the 

 punch, so that there may be sufficient clearance. In using 



