Fatigue Endurance Limit⚠ unverified
Physics / Materials · Estimate the corrected fatigue endurance limit using knockdown factors
Parameters
| Input | Symbol | Unit | Default | Description |
|---|---|---|---|---|
| ultimate_strength | ultimatestrength | Pa | 1.0 | Ultimate tensile strength of the material |
| surface_finish_factor | surfacefinishfactor | — | 1.0 | Surface-finish modification factor, dimensionless. Default is 1.0 |
| size_factor | sizefactor | — | 1.0 | Size modification factor, dimensionless. Default is 1.0 |
| load_factor | loadfactor | — | 1.0 | Loading-type modification factor, dimensionless. Default is 1.0 |
| temperature_factor | temperaturefactor | — | 1.0 | Temperature modification factor, dimensionless. Default is 1.0 |
| reliability_factor | reliabilityfactor | — | 1.0 | Reliability modification factor, dimensionless. Default is 1.0 |
| miscellaneous_factor | miscellaneousfactor | — | 1.0 | Miscellaneous-effects modification factor, dimensionless. Default is 1.0 |
| Output | Symbol | Unit | Description |
|---|---|---|---|
| result | Se | Pa | Corrected endurance limit, in pascals (Pa) |
The science & history
Understanding the Parameters
-
$0.5 S_{ut}$ — rough steel baseline (not for all alloys; aluminium often has no true endurance limit).
-
Marin factors — each $\le 1$ typically reduces $S_e$ from the polished lab specimen.
- $S_e$ — infinite-life amplitude stress for fully reversed bending under the assumptions used.
Derivation (Approaching a Proof)
Empirical: fatigue data show a plateau for many steels; design practice scales a fraction of $S_{ut}$ by product of modifying factors (Shigley/Marin). Not a first-principles continuum result.
History
Wöhler curves and endurance limits founded machine design fatigue practice; Marin factors are modern textbook packaging.
Related Concepts: Factor of Safety, Stress Intensity Factor, Von Mises Stress
Notes: Registry calculator fatigue-endurance-limit (unverified). Heuristic steel-oriented
estimate; factors user-supplied.