Soderberg Method Fatigue Curve Equation

Strength and Mechanics of Materials

Soderberg Equation Method for Fatigue

( σ_a / σ_e ) + ( σ_m / S_y ) = 1

( τ_a / τ_e ) + ( τ_m / S_YS ) = 1

Where:

σ_a, τ_a = Amplitude of normal (shear) stress [MPa, psi]

σ_e, τ_e = Endurance limit at constant strength [MPa, psi]

σ_m = Mean cycle stress [MPa, psi]

τ_m = Yield tensile strength [MPa, psi]

S_y = Yield tensile strength [MPa, psi]

S_YS = Yield shear strength [MPa,psi] when S_YS ≈ .577 S_y

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Source:

Budynas, Richard G., and J. Keith Nisbett, Shigley's Mechanical Engineering Design, 8th ed., New York: McGraw-Hill, 2008.