Mohr circle for 3dimensional stress state

[chandran]

I am not sure how to draw a mohr cirlcle on a 3d stress state. I haven't seen
any website sofar. Is it being used by engineers these days or some alternate
method is available.

 

[Gokul43201]

I doubt that many engineers actually use the Mohr Circle analysis anymore. There are so many neat Finite Element modeling packages out there that the art of doing stress analysis by hand is virtually extinct.

 

[FredGarvin]

I use it occasionally, just to keep my head into the theory and if the problem is simple enough.

A 2 second search yielded the following
http://me.queensu.ca/courses/MECH422/Lecture5a.ppt
http://portal.cs.umass.edu/projects/mohr/
http://www.utm.edu/departments/engin/lemaster/Machine%20Design/Lecture%2003.pdf

There's plenty of information out there on how to do this technique.

 

[chandran]

fred,

unfortunately the links doesn't tell me how to draw the three circles from
the scratch. Can you pls.

 

[FredGarvin]

Are you familiar or have studied the two dimensional Mohr's circle?

 

[chandran]

fred.
I have studied plane stress state(i.e 2d) and know how to draw a 2d mohr
circle.

 

[FredGarvin]

Here's a quickie:

http://www.aoe.vt.edu/~jing/java/nsfapplets/MohrCircles2-3D/Theory/theory.htm

This is from the same site that has an appelet to draw them for you:
http://www.aoe.vt.edu/~jing/java/nsfapplets/MohrCircles2-3D/Applets/applet.htm

 

[chandran]

in this link there is reference to the eigen value. example they say "the
two principle stresses are the eigne value of the 2x2 matrix of sigmax and tauxy"

I was looking for a practical application of eigen value. can you now tell this
what is an eigen value?

 

[chandran]

fred,
I am not getting it. How to draw the 3 circles(centre and diameter of the circles).

 

[omgitsroy326]

eigen value can help with the mohr circle but it's really really long from what i jus reviewed... anyhow i have a book that explains ti and i dont' have a digital camera but this book is pretty good...

Mechanics of Material by Ferdinand P Beer

from the book it gives
sigY = 3.5
Sigx = 6
txy = - 3ksi

The book I'm lookin at develops the mohr circle by tne normal sigAVE(4.75ksi) equation
from that you know the center of circle and the radius (3.25ksi) etc

Now the bigger circle comes from the principla streseses
which is 8ksi and 1.5ksi.
now from 0 to 8 is the new diameter of the third circle
and from 0 to 1.5 is the small circle
and from 1.5 to 8 is the medium circle...

das what the book has and i guess the key is your principle stress...

 

[col_chris16]

Hi Guys,

Can someone advise me how you would find the sigma(x), sigma(y), tau(xy) values?


Chris


p.s.
also...is the following equation valid for 3d models...

Smax= 0.5*(Sx-Sy) + 0.5*(sqrt( ((Sx-Sy)^2) + (4*Tauxy^2) )