Muddy Card Responses Lecture M15
What is “principle stress”
First up it should be “princip
a
l”  a pet hate of mine. The
principal stresses are the maximum and minimum (extremum) extensional (norma) stresses
in a stress state at a point. The principal directions are the corresponding directions. The
principal directions have no shear stresses associated with them
More explanation of Mohr’s circle. How do we know what to plot where?
I have put a
step by step guide in the notes. If you follow this you should be able to do it correctly.
Are there any readings that would help explain some of these concepts.
Yes. If you look at
assignments with each lecture. The material we are covering now is covered in Crandall,
Dahl and Lardner chapter 4. It is worth looking at. Beware that CDL use a different notation
for stress which we will discuss in the next lecture or so.
On the second Mohr’s circle concept question, would the two most popular choices (#1
and #2) produce the same circle? Since they are simply rotations of one another, I would
expect that the circle is defined to be the same, Why, then, was it wrong to answer #2?
It is
true that all of the answers produced circles of radius 50 MPa centered on the origin.
However, in the circle given, the direction of
s
21
was defined. This mean that the correct
stress state was acting at 45° to answer #2. Note although the circles are identical, the
directions are not – and the directions matter (in fact they are the most important feature of
the Mohr’s circle.
2nd PRs question not clear.
See comments above.
M&S is cool .
I am very glad that you
think so!
For Mohr’s circle:
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View Full DocumentWhen you draw the rotated diameter it seems you just reflected it about the xaxis, but
that’s not what it really is right?
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 Winter '12
 CharlesColeman
 Force, Aeronautics, Astronautics, Shear Stress, Mohr’s circle

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