IKON AND STEEL 221 



The tensile strength in pounds per square inch is computed by 

 dividing the load read from the scalebeam by the area of cross section 

 of the test specimen (see Article 20). Expressed as a formula, 



2 load from scalebeam 



Tensile strength 111 lb./in. 2 = -- -. 



area of cross section 



168. Compression tests. To make compression tests the piece is 

 placed on a small block resting on the platform, and the lower cross- 

 head, provided with a similar block, is brought down upon it. The 

 further lowering of the crosshead compresses the specimen. The pres- 

 sure comes on the platform through the crossbeam that rests upon it, 

 and is transmitted to the scalebeam, where it is measured. 



The compressive strength in lb./in. 2 is computed by dividing the load 

 in pounds as read on the scalebeam by the area of cross section of 

 the test specimen, as in finding the tensile strength. 



169. Flexure tests. Beams are tested in flexure by mounting the 

 specimen on a crossbeam provided with knife-edges and applying the 

 load from above by means of a knife-edge attached to the under side 

 of the moving head. The beam is tested by lowering the moving 

 head as in the compression tests. 



The fiber stress in the outer fiber of the beam is computed in this 

 case from the formula (see Article 52), 



Pie 



where e is the distance from the neutral axis to the outer fiber, / is 

 the moment of inertia with reference to the neutral axis, P is the 

 load in pounds as read from the scalebeam, / is the length of the span 

 in inches, and p is the fiber stress in lb./in. 2 . 



The maximum deflection for the concentrated central load is com- 

 puted by the formula (see Article 66), 



48 El 



where D is the deflection at the center, E the modulus of elas- 

 ticity (see Article 8), and P, I, and / have the same meaning as 

 above. 



