Using Mohr's Circle to Find Principal Stresses and Angles - dummies

Using Mohr’s Circle to Find Principal Stresses and Angles

By James H. Allen, III

Part of Mechanics of Materials For Dummies Cheat Sheet

Anyone in the mechanical sciences is likely familiar with Mohrs circle — a useful graphical technique for finding principal stresses and strains in materials. Mohr’s circle also tells you the principal angles (orientations) of the principal stresses without your having to plug an angle into stress transformation equations.






  4. Sketch the circle around the diameter from Step 3.



  5. Compute the normal stress position for the circle’s center point (C).


  6. Calculate the radius (R) for the circle.


  7. Determine the principal stresses σP1 and σP2.


  8. Compute the principal angles ΘP1 and ΘP2.


You could also use equations directly (instead of Mohr’s circle) to determine transformed stresses at any angle:

