Fatigue Life Calculator
Estimate the number of load cycles to failure using a simplified S-N curve approach (Basquin relation).
Cycles to Failure (Nf)
3,405,063 cycles
Cycles to Failure (Nf) vs Stress Amplitude (Sa)
Formula
## Fatigue Life Estimation (Basquin Relation) Repetitive loading below the static strength can cause failure through fatigue crack growth. ### Formula **Sa = Sf' (2Nf)^b** or equivalently **Nf = 0.5 (Sa / Sf')^(1/b)** This simplified form (Basquin equation) relates stress amplitude Sa to cycles to failure Nf. The fatigue strength coefficient Sf' and exponent b are material properties obtained from testing. Typical b values range from -0.05 to -0.15.
Exemplo Resolvido
A steel component with Sf'=900 MPa, b=-0.1, subjected to 200 MPa stress amplitude.
- 01Sa/Sf' = 200/900 = 0.2222
- 021/b = 1/(-0.1) = -10
- 03Nf = (0.2222)^(-10) = approximately 6,046,618 cycles
- 04This is above 10^6, suggesting effectively infinite life for many applications.
Perguntas Frequentes
What is the endurance limit?
Some materials (notably ferrous metals) have an endurance limit below which fatigue failure does not occur regardless of cycle count. For steel, this is typically about 40-50% of the ultimate tensile strength.
Does surface finish affect fatigue life?
Significantly. Rough surfaces, scratches, and corrosion pits act as stress concentrators that initiate fatigue cracks. Polished surfaces can have 2-3 times the fatigue life of machined surfaces.
How do I account for mean stress?
Use the Goodman, Soderberg, or Gerber correction to adjust the stress amplitude for non-zero mean stress. The Goodman approach: Sa_eff = Sa / (1 - Sm/Su), where Sm is mean stress and Su is ultimate strength.
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