Von Mises stress theory evaluates what kind of stress under what loading condition?

• A. Maximum normal stress
• B. Equivalent stress under combined loading
• C. Hydrostatic stress
• D. Shear stress amplitude

Answer: (B)

Von Mises stress theory uses distortion energy to predict yielding under any multi-axial loading state. It converts a complex 3D stress state into a single scalar value, the equivalent (von Mises) stress, which represents the level of distortion energy in the material. When this equivalent stress reaches the material’s yield strength, yielding is predicted. This makes the criterion especially suited for combined loading, because it accounts for the combined effects of normal and shear stresses, not just the largest normal stress.

In uniaxial tension, the von Mises stress equals the actual applied stress, so it matches the familiar yield concept there. Hydrostatic stress, on the other hand, does not contribute to distortion energy and thus does not drive yielding in this criterion. Likewise, simply considering shear stress amplitude is not sufficient by itself—the von Mises value blends the contributions of all stress components into one representative measure of distortion energy under the full loading state.