Lecture 23
Example Problem
Drawing a Stress Prism
Given:
a 1" x 2" block is loaded with 1000#
Determine:
the magnitude of the stress and draw the stress prism
Solution: Knowing that the internal stress f = P/A , simply take the 1000 pounds and divide it by the area of the element. 1000# / 2 in^2 = 500 psi The stress is evenly distributed over the cross-section with a magnitude of 500 psi. If the volume
of the stress prism is determined it can be seen that it is the same as the total load on the section. Volume = width x length x height; = 1 inch x 2 inches x 500 psi = 1000 pounds.
Note: The even distribution of this axial load is represented by a simple rectangular stress prism. If the load was moved to one side of the axis the stress prism would also have to change in response to the changing state of stress within the se
ction. The prism would deepen on the side that the load was being applied and reduce in size on the opposite side. This would continue until the sign of the stress would actually change, indicating that part of the cross section was no longer in compres
sion, but in tension to maintain equilibrium.
Copyright © 1995 by Chris H. Luebkeman and Donald Peting