Equivalent stress is related to the principal stresses by the equation:
Equivalent stress (also called von Mises stress) is often used in design work because it allows any arbitrary three-dimensional stress state to be represented as a single positive stress value. Equivalent stress is part of the maximum equivalent stress failure theory used to predict yielding in a ductile material.
The von Mises or equivalent strain εe is computed as:
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where:
ν' = effective Poisson's ratio, which is defined as follows:
Material Poisson's ratio for elastic and thermal strains computed at the reference temperature of the body.
0.5 for plastic strains.
Note: Currently, for Linked MSUP analyses with the Expand Results From detail under Output Controls set to Modal Solution, the Mechanical APDL solver does not calculate equivalent strains. If you choose to display equivalent strain results, you will see zero contours.