Equivalent Stress

Equivalent Stress

The stress results of a FE analysis are three-dimensional tensors, see:

Stress Tensor

Material properties including Yield Strength and Ultimate Strength are however usually derived from uniaxial tests, e.g. tensile tests, see:

Tensile Tests

Depending on the material used and its failure mode, there are different conversions done:

  • For ductile materials (e.g. many commonly used metals), the Von Mises stress is calculated.¬†This is the most common equivalent stress in mechanical engineering and hence frequently referred to as the Equivalent Stress (although there are others).
  • Some pressure vessel codes require Tresca Stress to be used.
  • Ceramics (including glass) have a high compressive strength but a low tensile strength. That is why the Maximum Principal Stress is used to asses these materials.
  • Fibre Reinforced Plastics (FRP) are strong in tension but less strong in compression. That is why they are compared to the Minimum Principal Stress.
  • Particular equivalent stresses might be required for certain engineering codes.

FEA programs convert the stress tensor automatically to the desired equivalent stress. When reviewing a FEA stress report, it is however important to ensure that the appropriate equivalent stress has been applied.

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