Mohr's Circle for Stress

What am I seeing?

• Every point on the circle is the same physical stress state, viewed on a different cutting plane.
• Rotate the element by θ and the stress point travels 2θ around the circle in the same sense, because τ is plotted positive downwards.
• The circle crosses the σ axis at the principal stresses σ₁ and σ₂, where the shear stress vanishes.
• The radius equals the maximum in-plane shear stress, found on planes 45° from the principal planes.
• Press Sweep θ and watch the element and the circle move together.