Variables
Description
What is this formula?
The Basquin Equation relates the stress amplitude applied to a material and the number of cycles required to cause fatigue failure. It is one of the most widely used models for high-cycle fatigue analysis.
When to use it
Use this equation when estimating the fatigue life of components subjected to repeated elastic loading, especially when the number of cycles exceeds approximately 10,000 and plastic deformation is minimal.
Example
A steel specimen has:
sigmaf = 1000 MPa
b = -0.10
sigmaa = 400 MPa
Formula:
sigmaa = sigmaf*(Nf^b)
Solving for fatigue life:
Nf = (sigmaa/sigmaf)^(1/b)
Substitution:
Nf = (400/1000)^(1/(-0.10))
Result:
Nf = 9537 cycles
The component is expected to fail after approximately 9,537 loading cycles.
Applications
- High-cycle fatigue analysis
- Mechanical component design
- Automotive engineering
- Aerospace structures
- Rotating machinery
- Structural durability assessment
Note
The Basquin Equation is an empirical model derived from S-N fatigue testing. It is primarily applicable in the high-cycle fatigue region where elastic strains dominate. Different materials require experimentally determined values of sigmaf and b, and alternative models may be needed when significant plastic deformation occurs.