Abstract
An experimental study is presented for cyclic plastic stresses at notch roots in specimens under constant-amplitude repeated tension and reversed loading. Edge-notched,K T=2, 2024-T3 aluminum-alloy sheet specimens were cycled until local stress conditions stabilized. Local stress histories were determined by recording local strain histories during cycling and reproducting these histories in simple, unnotched specimens. The fatigue lives for these notched specimens were estimated using stabilized local stresses and an alternating vs. mean stress diagram for unnotched specimens of the same material. These predictions compared favorably with lives from S-N data for the notch configuration tested.
In addition, an expression is presented for calculating local first-cycle plastic stresses. An acceptable correlation is shown between predicted stresses and experimental data within the scope of the investigation.
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Abbreviations
- E s :
-
secant modulus corresponding to the local stress at the notch root for monotonically increasing tensile loads, psi
- E s′:
-
secant modulus corresponding to the local stress at the notch root for negative loading from tension. psi
- E s″:
-
secant modulus corresponding to the local stress at the notch root for positive loading from compression, psi
- E ∞ :
-
secant modulus corresponding to the average stress on the net section, psi
- K p :
-
plastic stress-concentration factor for monotonically increasing tensile loads
- K p′:
-
plastic stress-concentration factor for negative loading from tension
- K p″:
-
plastic stress-concentration factor for positive loading from compression
- K T :
-
elastic stress-concentration factor
- N :
-
number of cycles
- R :
-
ratio of Smin/Smax
- S :
-
nominal net-section stress, ksi
- S max :
-
maximum nominal net-section stress, ksi
- S min :
-
minimum nominal net-section stress, ksi
- ΔS :
-
nominal stress range, ksi
- t :
-
specimen thickness, in.
- ε:
-
local strain at the notch root
- ρ:
-
notch-root radius, in.
- σ:
-
local stress at the notch root, ksi
- σ r :
-
local residual stress at the notch root, ksi
References
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Illg, W., Fatigue Tests on Notched and Unnotched Sheet Specimens of 2024-T3 and 7075-T6 Aluminum Alloys and of SAE 4130 Steel With Special Consideration of the Life Range From 2 to 10,000 Cycles, NACA TN 3866 (1956).
Grover, H. J., Bishop, S. M., and Jackson, L. R., Fatigue Strengths of Aircraft Materials. Axial-Load Fatigue Tests on Notched Sheet Specimens of 24S-T3 and 75S-T6 Aluminum Alloys and of SAE 4130 Steel With Stress-Concentration Factors of 2.0 and 4.0, NACA TN 2389 (1951).
Grover, H. J., Hyler, W. S., Kuhn, P., Landers, C. B., and Howell, F. M., Axial-Load Fatigue Properties of 24S-T and 75S-T Aluminum Alloy as Determined in Several Laboratories, NACA Report 1190 (1954).
Stowell, E. Z., Stress and Strain Concentration at a Circular Hole in an Infinite Plate, NACA TN 2073 (1950).
Hardrath, H. F., and Ohman, L., A Study of Elastic and Plastic Stress Concentration Factors Due to Notches and Fillets in Flat Plates, NACA Report 1117 (1953).
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Crews, J.H., Hardrath, H.F. A study of cyclic plastic stresses at a notch root. Experimental Mechanics 6, 313–320 (1966). https://doi.org/10.1007/BF02327511
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DOI: https://doi.org/10.1007/BF02327511