Wednesday, April 30, 2008

Microsoft Excel VBA - Mohr's Circle for Plane Stress

The German engineer Otto Mohr (1835-1918) developed a useful pictorial or graphical interpretation of the equations for finding the principal stresses and the maximum shearing stress at a point in a stressed member. This method, commonly called Mohr's circle, involves the construction of a circle in such a manner that the coordinates of each point on the circle represent the normal and shearing stresses on one plane through the stressed point, and the angular position of the radius to the point gives the orientation of the plane.



Normal stresses are plotted as horizontal coordinates, with tensile stresses (positive) plotted to the right of the origin and compressive stresses (negative) plotted to the left. Shearing stresses are plotted as vertical coordinates, with those tending to produce a clockwise rotation of the stress element plotted above the s axis, and those tending to produce a counterclockwise rotation of the stress element plotted below the s axis.

The results obtained from Mohr's circle are identical with the equation derived from the free-body diagram. Consequently, Mohr's circle provides an extremely useful aid in the solution for, and visualization of, the stresses on various planes through a point in a stressed body in terms of the stresses on two mutually perpendicular planes through the point. Although Mohr's circle can be drawn to scale and used to obtain values of stresses and angles by direct measurements on the figure, it is probably more useful as a pictorial aid to the analyst who is performing analytical determinations of stresses and their directions at the point.



Useful information about Mohr's Circle:
You can download Mohr's Circle Excel file for free with password: mechanical-design-handbook.blogspot.com

DOWNLOAD Mohr's Circle Excel file for FREE

10 comments:

dbf064 said...

How do i get it to show mohr's circle plotted in the negative x direction? The graph is not shown fully in the diagram.

Ake Blogger said...

Hi

You have to "Enable macros" when opening the excel file.

Please note that if you don't follow these steps, you may not be able to run the macro.

1) Tools > Macro > Security
2) Security Level tab > Medium. > OK
3) Close Microsoft Excel
4) Open the file again and you will see the pop-up
5) Select Enable Macros

Note: step 1 -3, you have to do only once, later you can skip them

I hope this helps.

Ake

stviolet said...

hi ake, love your program,
is it possible for you to include a square diagram with normal stress, shear stress and angels?

i get really confused when relating angle and rotation on square TO morh's circle's angles and rotation.

could you contact me if you can be bothered? slxia1@student.monash.edu.au

Ripu said...

HOW DO I GET TO ACCESS THE CODE WRITTEN. IT IS ASKING FOR A PASSWORD.

gavin davis said...

Lovely program. few concerns, if anyone is still managing the comments. A mohr's stress circle should only be one circle with both the shear and normal stress axis to the same scale. I'm not quite sure what the second circle is for. The maximum shear stress for the values entered would be approx 129 Mpa. The angle for the maximum shear stress is correct but i'm not sure how this maximum shear stress value is being calculated or i'm mis-interpreting something.

Justin Mayer said...

Is there a chance i could get a copy of the code?

j.mayer@my.und.edu

Clairina Piink said...

Hi everybody
I'm a french student and I would like to have this program on excel for a project in mechanical engineering.

Please can someone send me this program.

Thanks

Alexander Blastique said...

To Ake Blogger,
I wish to download a copy of your Mohr's Circle program for academic purpose. I cannot download it through the link provided. Thank you. Can you post another link please.

Flo rent said...

The link to download the file is dead... I need it but I don't find it...

Mauricio Oliveira said...

Withc is the password?