KEVOS® MAKEOS · Strength
Fatigue Notch Factor from Stress Concentration
How much does this notch, fillet or groove reduce fatigue strength?
Notch sensitivity (Peterson) and the fatigue stress concentration factor Kf from the theoretical factor Kt, the notch radius and the material’s tensile strength or characteristic length.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Theoretical stress concentration factor Kt | Elastic stress concentration factor for the geometry from charts or FEA. | |
| Notch root radius | mm | Radius at the root of the notch, fillet or groove. |
| Material constant | choice | Estimate the material constant for steels, or enter it. |
| Tensile strength (steel estimate) | MPa | Ultimate tensile strength (used for the steel estimate). |
| Peterson constant a | mm | Peterson’s characteristic length for the material from fatigue data (entered mode). |
Method and formulas
- Steel estimate: a ≈ 0.0254 × (2070 ÷ Su)^1.8 mm (Su in MPa).
- Peterson: q = 1 ÷ (1 + a/r).
- Kf = 1 + q (Kt − 1); multiply nominal alternating stress by Kf.
- Example: Kt 2.2 with a 1 mm radius in 700 MPa steel gives q = 0.84831 and Kf = 2.018.
Limitations
- Empirical notch sensitivity; for very small radii or high-strength steels use measured data.
- Kt must match the load type (bending, axial or torsion).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Turn a chart Kt into the effective fatigue factor
- Compare fillet radii on a shaft shoulder
- Feed the Goodman fatigue tool
Who it is for
- Design engineers
- Structural and mechanical engineers
- Engineering students
What you get
- Notch sensitivity q
- Fatigue factor Kf
- Reduction compared with Kt
Interpreting the result
- A larger radius lowers Kt and gives the material less notch sensitivity benefit; both effects are captured here.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 200–211. Topic reference; no source tables or recommended settings are reproduced.
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