1GS 



PUNCHING TESTS. 



these in a testing machine the punch is fixed to the upper 

 compression plate, and the bolster to the lower one. The 

 piece punched out is slightly conical in shape, but it is 

 usual to take the diameter of the circle upon which the 

 shear takes place as that of the cutting edge of the punch. 

 The operation itself is simple. It is only necessary to 



place the specimen beneath the punch upon the bolster, 

 and then to bring the two together and increase the load 

 until the failure has taken place by the punch shearing 

 the piece out of the plate. The following is an example 

 of such a test. In this case the tensile strength of the 

 same plate has been previously ascertained. 



PUNCHING TEST. 



The shearing area is 



a = diameter of punch x 3*141 x thickness of plate 



= 1 x 3-141 x 0*39. 

 = 1-22 sq. in. 



The shearing stress = Aching load 



a 



32 

 1-22 



= 26*20 tons per sq. in. 



