STRENGTH OF WROUGHT IRON. 



355 



The conclusions arrived at from these tests are : 



(1) That high compressive strains applied to iron bars 

 result in raising the limit of elasticity in tension, and that 

 the tension limit may be changed from 61 to 91 per cent, 

 of the maximum tensile strength by increasing the 

 intensity of the compressive stress applied. 



('2) That the tension modulus of elasticity is slightly 

 lowered by the application of a high compressive stress. 



(3) That a ductile iron bar presenting a perfectly 

 fibrous fracture will, after the application of excessive 

 compressive stress, be entirely changed to give a fracture 



FIG. 177. 



of 100 per cent, crystalline area, almost similar in appear- 

 ance to that of cast iron. That the proportion of fibrous 

 to crystalline area is diminished as the compressive stress 

 is increased. 



(4) That annealing a compressed bar restores it to a 

 fibrous state. 



On Fig. 173, the curve marked A is that of a specimen 

 of the uncompressed iron ; its fibrous laminated fracture 

 is shown on Fig. 175. 



The curve B is for a specimen cut from a compressed 

 tyre, and straightened cold. The fracture of this bar is 



