2M The Rupture of Steel by Longitudinal Strest. 



FIG. 6. 



the contracted section. The result is, that in flat bars of soft steel 

 the fracture is almost invariably as shown in figs. 4 and 5, 

 Plate 3. Fig. 8, Plate 3, shows a flat bar of soft steel 

 about to rupture by shearing along a plane _|_ the width of the 

 resulting no doubt from an accidental weakness in that direction. 



In the cases considered above, the steel has been of sufficient]] 

 uniform quality to allow of the fracture taking place over a surfs 

 of least resistance to shearing ; but, unless this condition be fulfill* 

 the form of the fracture will be quite different. 



Figs. 7 and 8, Plate 2, show the fracture of a brass bar wher 

 the plane of least resistance to shearing has been determined by 

 punch mark (opposite the arrow) on the surface. Fig. 1, Plate 2, shot 

 a steel bar where the apex of the cone is at the circnmferenc 

 owing to the presence of a weak spot there. 



Every fracture is caused by the presence of a more or less wt 

 defined weak spot; the stress is greatest at this spot, and the matei 

 tends to tear in a plane J_ the axis passing through this spot, 

 tearing action can be observed by drilling a small hole in a stt 

 plate, and straining it. The plate pinches in near the hole, at 

 gives way first on each side of the hole, and then tears right 

 The experiment may be stopped before the tear has reached 

 sides. 



When the steel is hard, this tearing continues in the plane 



