Fig. 3240.
“By carrying out this process we shall perceive that, although the pressure acts upon the whole circumference, yet its effectiveness in bursting the boiler in any one direction is equal to the boiler diameter. Thus in [Fig. 3240], the pressure acting in the direction of the arrows a (and to burst the boiler apart at b b) is represented by the diametral line b b, while the pressure actually exerted upon the whole boiler shell is represented by the circumference of the boiler.
“To proceed, then, it will now be clear that the ultimate strength of the boiler material, multiplied by twice the thickness of the boiler shell plate in inches or decimal parts of an inch, and this sum divided by the internal diameter of the boiler, in inches, gives the pressure (in lbs. per square inch) at which the boiler shell will burst.”
We have here only considered the strength of the solid plate of the shell, and may now consider the strength of the riveted joints, because, as the boiler cannot be any stronger as a whole than its weakest part is, and as the riveted joints are the weakest parts of a cylindrical boiler,[51] therefore the strength of the riveted joint determines the strength of the boiler.
[51] It may be here noted that the riveted joint of a flat plate is stronger than the flat surface of the plate, because at the joint the plate is doubled, or one plate overlaps the other.
[52]“The strains to which a riveted joint is subjected are as follows: That acting to shear the rivet across its diameter is called the shearing strain. But the same strain acts to tear the plate apart; hence, when spoken of with reference to the action on the plate, it is called the tearing strain.
[52] From “Steam Boilers.”
“The same strain also acts to crush and rupture the plate between the rivet hole and the edge of the plate, and in this connection it is called the crushing strain.