Steel Endurance Limit

Overview

The endurance limit (fatigue limit) is the maximum stress amplitude a material can withstand for an infinite number of cycles without failure.

Formula

$S_e' \approx 0.5 S_{ut}$

Calculator

Notes

• Results are approximate and should be verified for critical applications
• Input values should be within reasonable engineering ranges

Key Concepts

Fatigue

Failure of a material due to repeated cycles of stress or strain, occurring at stress levels below the material's yield strength. This is a common failure mode in cyclically loaded components like connecting rods, crankshafts, and turbine blades.

Creep

Time-dependent deformation of a material under a sustained load over a long period. Creep strength generally decreases with increasing temperature. For steel bolts and piping, a typical allowable creep strain specification is ~0.1%/year.

Important Material Properties

• Yield Strength (σ_y): The stress at which a material transitions from elastic to plastic deformation.
• Tensile Strength (σ_u or UTS): The maximum stress a material can withstand while being stretched before necking and breaking.
• Endurance Limit (σ_e): The maximum cyclic stress amplitude a material can endure for an "infinite" number of cycles without fatigue failure. Also called the fatigue limit.

Formula: General Relationship

For many steels, a useful rule of thumb for the endurance limit is:

$\sigma_e \approx \frac{\sigma_u}{2}$

This relationship is approximate and varies based on steel composition, treatment, and surface finish, as shown in the table above (where the ratio $\sigma_e / \sigma_u$ ranges from 0.41 to 0.53).

Interactive Charts

References

• Original Source