Evaluate notch effects using fatigue concentration factors accurately. Compare direct sensitivity and Peterson radius methods. Visualize stress amplification trends with exports, examples, and guidance.
Use direct q input or Peterson radius method.
The chart tracks how Kf and local alternating stress change as q varies from 0 to 1.
| Component | Kt | q | Kf | Nominal Alt. Stress | Local Alt. Stress |
|---|---|---|---|---|---|
| Grooved shaft | 1.90 | 0.55 | 1.495 | 48.00 MPa | 71.76 MPa |
| Shoulder fillet | 2.20 | 0.68 | 1.816 | 72.00 MPa | 130.75 MPa |
| Keyway section | 2.75 | 0.74 | 2.295 | 90.00 MPa | 206.55 MPa |
| Thread root | 3.10 | 0.82 | 2.722 | 110.00 MPa | 299.42 MPa |
These rows show how sharper notches and higher q values raise local fatigue stress.
The fatigue stress concentration factor connects the theoretical notch effect to the real fatigue response of a material.
Where:
For Peterson approximation:
Where:
Local alternating stress is estimated with:
Goodman safety estimate used here:
It is the factor that amplifies nominal cyclic stress at a notch during fatigue loading. Unlike Kt, it includes material sensitivity through q, so it better reflects actual fatigue behavior.
Real materials are not perfectly notch sensitive. Because q is often below 1, the fatigue response does not fully reach the theoretical elastic concentration, so Kf remains lower than Kt.
q measures how strongly a material reacts to a notch under cyclic loading. A value near 0 means weak sensitivity. A value near 1 means fatigue behavior nearly follows the theoretical notch effect.
Use Peterson approximation when you know the notch radius and an appropriate material constant a. It offers a practical way to estimate q when direct notch sensitivity data is unavailable.
Yes. Mean stress changes fatigue margin significantly. Tensile mean stress usually reduces life, which is why this calculator includes a Goodman-based safety estimate alongside Kf and local alternating stress.
No, not in the standard relation used here. Since Kt is at least 1 and q stays between 0 and 1, Kf remains 1 or greater.
Accurate Kt, realistic q or Peterson data, and properly corrected endurance properties matter most. Poor notch geometry estimates can easily shift Kf and local stress predictions.
It is a strong screening tool, not a replacement for full fatigue verification. Final approval should consider surface finish, size effects, residual stress, multiaxial loading, and validated material data.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.