Determination of cyclic R-curve for predicting short fatigue crack growth

• Published in: Theoretical and applied fracture mechanics Vol. 133; p. 104544
• Main Authors: Tanaka, K., Akiniwa, Y.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-10-2024
• Subjects: Compression precracking; Crack closure; Crack growth threshold; Fatigue limit; Short crack propagation; Strip-yield model; Short crack propagation; Crack growth threshold; Compression precracking; Fatigue limit; Strip-yield model; Crack closure
• ISSN: 0167-8442
• DOI: 10.1016/j.tafmec.2024.104544

•The effects of precrack length and material yield stress on the cyclic R curve are clarified, and fitting functions are proposed for R-curve.•Proper experimental procedure to determine the cyclic R-curve is discussed based on simulations.•A new method is proposed to estimate crack closure for propagating cracks based on R-curve data.
The development of plasticity-induced crack closure with crack extension from open precracks is simulated using a strip-yield model to leave plastically deformed stretch in the wake of the advancing crack faces under fully reversed loading. Under the assumption of a constant value of the effective threshold range for steels, the effects of precrack length and material yield stress on the cyclic R-curve are clarified using fitting functions proposed for R-curve. Proper experimental procedure to determine the cyclic R-curve is discussed based on simulations. The R-curve obtained using step-up constant amplitude loading of single specimen with a precrack is identical to that obtained by constant amplitude loading of multiple specimens. In compression precracking, the influence of tensile residual stress needs to be minimized, while the amount of crack extension in precracking required to have a certain length in order to get rid of the root radius effect of notches. A new method is proposed to estimate the buildup of crack closure for propagating cracks based on R-curve data.