KEVOS® MAKEOS · Strength
Fatigue Safety Factor (Goodman)
Is this fluctuating stress safe for infinite life by the Goodman, Soderberg and Gerber criteria?
Fatigue safety factors for combined alternating and mean stress by modified Goodman, Soderberg and Gerber, plus first-cycle yield, against a required factor.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Alternating stress amplitude σa | MPa | Half the stress range, including the fatigue stress concentration factor Kf. |
| Mean stress σm | MPa | Average of maximum and minimum stress (tension positive), including Kf where your method requires it. |
| Corrected endurance limit Se | MPa | Endurance limit corrected for surface, size, load, temperature and reliability, from test data or your design method. |
| Ultimate tensile strength | MPa | Ultimate tensile strength from the material certificate. |
| Yield strength | MPa | Minimum yield strength from the material certificate or specification, not a typical value. |
| Required safety factor | Factor of safety required by your design code, customer specification or company standard. |
Method and formulas
- Goodman: n = 1 ÷ (σa ÷ Se + σm ÷ Su). Soderberg: n = 1 ÷ (σa ÷ Se + σm ÷ Sy).
- Gerber: n = ½(Su ÷ σm)²(σa ÷ Se)[−1 + √(1 + (2σm Se ÷ (Su σa))²)].
- Compressive mean stress: n = Se ÷ σa. Yield (Langer): n = Sy ÷ (σa + |σm|).
- Example: σa 100 and σm 80 MPa with Se 220 and Su 600 MPa give a Goodman factor of 1.701.
Limitations
- Infinite-life (endurance) criteria for steels; materials without an endurance limit need a life-based method.
- The accuracy depends on the corrected endurance limit, which is the user’s responsibility.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check shafts, springs and brackets under cyclic load
- Compare mean-stress criteria
- Screen a design before testing
Who it is for
- Design engineers
- Structural and mechanical engineers
- Engineering students
What you get
- Goodman, Soderberg and Gerber safety factors
- First-cycle yield safety factor
- Governing factor
Interpreting the result
- Goodman is the usual design criterion; Gerber fits test data better; Soderberg is the most conservative.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 200–211, 280. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
