Fit a Curve by Estimating UTS
An empirical formula can be used to estimate SN/EN data from ultimate tensile strength (UTS) and Young's modulus (E).
- From the Assign Material dialog, click the My Material tab and select your created material.
- Select Estimate from UTS as the input method.
-
Click
to view the model description.
- Enter a value for UTS and Elastic modulus.
- Click Estimate.
SN Properties

- SRI1SRI1
- Fatigue strength coefficient. It is the stress amplitude intercept of the SN curve at 1 cycle on a log-log scale.
- b1b1
- The first fatigue strength exponent. The slope of the first segment of the SN curve in log-log scale.
- Nc1Nc1
- b2b2
- The second fatigue strength exponent.
Empirically, the life of a metal is 1000 when the stress amplitude is approximately 90% of the UTS. (S1000 = 0.9UTS) when loading type is a bending load.
According to "Engineering Considerations of Stress, Strain, and Strength" by Juvinall RC, 1976, McGraw-Hill, fatigue limit (FL) can be estimated as follows:
- For steel that has pearlite microstructure, FL = 0.38UTS at Nc1 = 1E6
- For aluminum alloys whose UTS < 336MPa, FL = 0.4UTS at Nc1 = 5E8
- For Aluminum Alloys whose UTS >= 336MPa, FL = 130MPa at Nc1 = 5E8
With the above information, two points on the SN curve are known: (1000, S1000) and (Nc1, FL). Thus, slope can be calculated:
b1 = (log(0.9UTS) − log(FL)) / (log(1000) − log(Nc1))b1 = (log(0.9UTS) − log(FL)) / (log(1000) − log(Nc1))
Once b1 is known, SRI1 is calculated by:
2⋅S1000=SRI1⋅(1000)b12⋅S1000=SRI1⋅(1000)b1
(The stress range 2*S1000 is used.) Therefore,
SRI1=2⋅S1000/(1000b1)SRI1=2⋅S1000/(1000b1)



EN Properties

- Sf/σ′fSf/σ′f
- Fatigue strength coefficient.
- bb
- Fatigue strength exponent.
- cc
- Fatigue ductility exponent.
- Ef/ε′fEf/ε′f
- Fatigue ductility coefficient.
- Np/n′Np/n′
- Cyclic strain-hardening exponent.
- Kp/K′Kp/K′
- Cyclic strength coefficient.
- NcNc
- Reversal limit of endurance. One cycle contains two reversals.
- SEeSEe
- Standard Error of Log(elastic strain).
- SEpSEp
- Standard Error of Log(plastic strain).
