The Rapture of Steel ly Longitudinal Stress. 



All these causes tend to reduce tlie superiority of the grooved bar ; 

 the effect of the non-uniformity of stress is, no doubt, the greatest ; 

 in fact, as has been shown, if the groove is of \/-shape, this causes 

 the plain bar to be the strongest, so that it is quite conceivable 

 that the non-uniformity of stress in the JJ-R roove( l bar, with other 

 causes mentioned, might reduce the strength from 180 : 100 to 

 120 : 100 of the plain bar. 



The following are the experiments referred to, in order to prove 

 that the ultimate resistance of steel to shearing diminishes inversely 

 with the drawing out : 



Six pieces of the same steel bar -were taken and drawn out under 

 tension to varying percentages of their length ; they were then pre- 

 pared as shearing specimens, as explained above, and tested in double 

 shear, with the following results : 



Table II. 



Thus the ultimate resistance to shearing increases with the drawing 

 out. Taking the contraction of area as a measure of the flow, No. 831 

 specimen contracted 50 per cent, on the plain bar and 28' 1 per cent. 

 on the (J -grooved bar, so that the former would be at an advantage, 

 compared with the latter, in this respect. 



It appears, then, that the load that can be borne by a given section 

 of steel without rupture can be increased by thickening the bar 

 above and below the section in question, though, if the angle of the 



)ove be too acute, the reverse is the effect. But the prejudicial 

 action of a groove, owing to non-uniformity of stress produced, is the 

 same in a \J- or \/-groove, and differs only in amount, so that the 

 I -groove, by itself, could not strengthen the bar, but must weaken 

 it; yet in spite of this, the \J -grooved bar is stronger than the plain 

 bar. The increase of strength, then, must be due to the added 



iterial ; but in no way could such added material strengthen such a 

 3ction, and enable it to stand a greater load, if rupture is produced 

 by a certain intensity of tensile stress ; we cannot diminish the mean 



3ss on the section by thickening the bar above and below ; on the 



