Mohr’s circle is the locus of points representing magnitude of normal andshear stress at various plane in a given stress element.Graphically, variation of normal stress and shear stress are studied with the help of Mohr's circle.
are Principal Stress then normal and shear stress on lane which is inclined at angle ‘θ’ from major principal plane, then
Normal stress:
Shear stress:
General State of Stress at an Element:
If 
are normal stress on vertical and horizontal plane respectively and this plane is accompanied by shear stress then normal stress and shear stress on plane, which is inclined at an angle θ from plane of
then,
Let be two normal stresses(both tensile) and 
be shear stress then,
Maximum and Minimum Principal Stresses are:
Radius of Mohr’s circle:
Strength of Materials
Observations from Mohr's Circle
The following are the observations of Mohr's circle as
* At point M on circle σn is maximum and shear stress is zero.
∴ Maximum principal stress ≡coordinate of M
* At point N on circle σn is minimum and shear stress τ is zero.
∴ minimum principal stress ≡ coordinate of N
* At point P on Circle τ is maximum.
Maximum shear stress ≡ ordinate of P(i.e. radius of circle)
Also, normal stress on plane of maximum shear stress
Where, σn ≡ Average stress
* Mohr's circle becomes zero at a point if radius of circle has the following consideration.
Radius of circle
* If σx = σy, then radius of Mohr's circle is zero and τxy = 0