Mohr's circle is a graphical method of visualizing the stress state at a point for various directions (planes). The principal stresses occur on a plane where the shear stress is zero. The maximum shear stress (or the Tresca stress) is equal to the radius of the circle (= 0.5*(maximum principal stress - minimum principal stress)). The stress intensity range is commonly used in pressure vessel design and is defined as (maximum principal stress - minimum principal stress). Since this is the diameter of Mohr's circle, the stress intensity range is equivalent to the Tresca*2 stress that is plotted in the Results environment.