Table of Contents
What Is Von Mises Stress?
The Von Mises stress (also called equivalent stress or effective stress) is a scalar value used to predict yielding of ductile materials under complex loading conditions. It combines the effects of all three principal stresses into a single equivalent value that can be compared directly to the material's uniaxial yield strength.
The Von Mises yield criterion states that yielding occurs when the Von Mises stress equals or exceeds the material's yield strength. This is based on the distortion energy theory, which assumes that yielding is caused by the shape-changing (deviatoric) part of the stress state, not the hydrostatic (volume-changing) part.
Von Mises Formula
Common Yield Strengths
| Material | Yield (MPa) |
|---|---|
| Mild Steel (A36) | 250 |
| Stainless 304 | 215 |
| Aluminum 6061-T6 | 276 |
| Titanium Ti-6Al-4V | 880 |
Frequently Asked Questions
When to use Von Mises vs Tresca?
Von Mises is more commonly used and slightly less conservative. Tresca (max shear stress) is simpler to apply and gives a safety factor about 15% lower than Von Mises. For ductile materials, Von Mises is generally more accurate.
Does Von Mises work for brittle materials?
No. Von Mises is for ductile materials. For brittle materials (cast iron, concrete, ceramics), use the maximum normal stress criterion (Rankine) or the Mohr-Coulomb criterion.
What does the safety factor mean?
Safety factor = Yield Strength / Von Mises Stress. A value above 1 means the material has not yielded. Most engineering designs require SF of 1.5 to 3.0 depending on the application and consequences of failure.