Safety factor calculation
The material stress limits are represented as the material yield strength or ultimate tensile strength. Safety factors are expressed as the ratio of the maximum strength of the material (Yield or Ultimate Tensile Strength) to the actual stress in the part (von Mises or 1st Principal Stress):
Safety Factor = Material Strength / Actual Stress
In Autodesk Fusion, the safety factor is calculated using one of the following two criteria:
- Yield Strength: This criterion is the default. The safety factor is calculated as the ratio yield strength / von Mises equivalent stress. The von Mises stress is a good predictor of failure, particularly for ductile materials like steel and aluminum. The factor must be greater than 1 for the design to be acceptable. (Less than 1 means that there is at least some permanent deformation, if not breakage.)
- Ultimate Tensile Strength: The safety factor is calculated as the ratio ultimate tensile strength / 1st principal stress (also known as the maximum principal stress). This method might be more appropriate for brittle materials that are not subject to yielding and less susceptible to fatigue.
Note: For temperature-dependent materials, the material strength is not a constant. To determine the safety factors throughout the model, Fusion uses the calculated temperatures and the nonlinear, temperature-dependent material data (yield or ultimate strength versus temperature). For temperatures that are between the data points in the material properties tables, the program interpolates the yield or ultimate strength value.