Mean Stress of a Fatigue Cycle
Mean Stress of a Fatigue Cycle
The mean stress of a fatigue cycle shifts the whole cycle up or down and, with the range, sets the fatigue damage.
The mean stress is σ_m = (σ_max + σ_min)/2. where σ_max and σ_min are the peak and trough stresses.
Inputs
sigma_max := 180 MPa=180 MPa
sigma_min := 40 MPa=40 MPa
Average the maximum and minimum.
sigma_m := (sigma_max + sigma_min)/2=110 MPa
Results
A tensile mean stress reduces fatigue life for a given range; compressive mean stress improves it — exploited by shot-peening.
Assumptions & limitations
- Constant-amplitude cycle.
- Uniaxial stress.
- Used with the range in Goodman analysis.