FULLY REVERSING FATIGUE PROCEDURE 1 FIND THE “RAW”

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Fully Reversing Fatigue Procedure

Find the “raw” endurance strength, S_e’

For steel, use:
Bending: S_e’ = 0.50 S_ut up to a max of 100 ksi

Axial: S_e’ = 0.45 S_ut up to a max of 90 ksi (Eqn. 7.7)
Torsion: S_e’ = 0.29 S_ut up to a max of 58 ksi
This is S_e’ for a polished 0.3” diameter bar.

D erate S_e’ to represent your application.

k_f Surface effect – if not polished

k_s Size effect – if not < 0.3” diameter

k_r Reliability effect – if other than 50% survival

k_t Temperature effect – if not at Room Temperature

k_m Miscellaneous – Mat’l processing, Residual stress, Coatings, Corrosion

S_e= k_f k_s k_r k_t k_m S_e’

(My Part) (Test Specimen)

3) Account for Stress Concentration with Notch Sensitivity
Compute K_f = 1 + (K_c –1)q_n and either divide S_e by K_f or multiply your actual alternating stress _alt by K_f.

4) Find the fatigue strength at the 1000 cycle Low Cycle Fatigue point, S_L’

For steel, use:
Bending: S_L’ = 0.90 S_ut

Axial: S_L’ = 0.75 S_ut (Eqn. 7.8)
Torsion: S_L’ = 0.72 S_ut

5) Build the S-N Curve

On Linear-Log paper, put: