EAS 209Fall 2010
Instructors: Christine Human
11/1/2010
1
Lecture 26 General State of Stress
Lecture 26
Effect of Third Principal Stress
So far we have only determined the stresses in the
xy plane, these are called the
inplane
stresses.
We have found that within this plane there are two
principal stresses.
However, there is actually a
third principal stress
(outofplane)
.
Today’s Objective:
Consider the effect of the third principal stress
Today’s Homework:
EAS 209Fall 2010
Instructors: Christine Human
11/1/2010
2
Lecture 26 General State of Stress
Third Principal Stress
The two principal stresses, points A and B
(obtained by rotation about the zaxis) in the figure
below are called the
inplane
principal stresses.
Remember however, that the stress element is 3
dimensional.
A third principal stress exists on a
plane that is perpendicular to the other two (in this
case the
z
axis).
Consequently we know that for
plane stress, the third principal stress,
σ
3
=0.
The third principal stress can be plotted as a point
at the origin.
This point can be connected to
points A and B to form two additional circles.
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 Spring '08
 Shear Stress, Stress, Lecture 26 General

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