Figure 1.
Kitagawa-Takahashi diagram showing the threshold for fatigue crack growth (cyclic resistance curve) in terms of stress range, after Ref [14[14] MILLER, K.J., “The two thresholds of fatigue behaviour”, Fatigue and Fracture of Engineering Materials and Structures, v. 16, n. 9, pp. 931–939, 1993.].
Figure 2.
(a) Resistance curve concept. (b) Fatigue endurance of the configuration.
Figure 3.
Crack closure model proposal for R-Curve estimation for short cracks. Δσth-a [18[18] ZERBST, U., SAVAIDIS, G., BEIER, H.T., “Special Issue on Fracture mechanics-based determination of the fatigue strength of weldments”, Engineering Fracture Mechanics, v. 198, pp. 1–208, 2018.,19[19] ZERBST, U., MADIA, M., SCHORK, B., et al., Fatigue and fracture of weldments. The IBESS approach for the determination of the fatigue life and strength of weldments by fracture mechanics analysis. Cham: Springer, 2019.].
Figure 4.
Chapetti model for R-Curve estimation for short cracks. Δσth-a.
Figure 3.
Crack closure model proposal for R-Curve estimation for short cracks. Δσth-a [18[18] ZERBST, U., SAVAIDIS, G., BEIER, H.T., “Special Issue on Fracture mechanics-based determination of the fatigue strength of weldments”, Engineering Fracture Mechanics, v. 198, pp. 1–208, 2018.,19[19] ZERBST, U., MADIA, M., SCHORK, B., et al., Fatigue and fracture of weldments. The IBESS approach for the determination of the fatigue life and strength of weldments by fracture mechanics analysis. Cham: Springer, 2019.].
Figure 4.
Chapetti model for R-Curve estimation for short cracks. Δσth-a.
Figure 5.
Cyclic R-curve concept and fatigue life configuration for estimations. (a) Present analysis, used also by Bergant [1[1] BERGANT, M., WERNER, T., MADIA, M., et al., “Short crack propagation analysis and fatigue strength assessment of additively manufactured materials: An application to AISI 316L”, International Journal of Fatigue, v. 151, 106396, 2021.]. (b) Alternative configuration used by Bergant when applying the Chapetti´s model [1[1] BERGANT, M., WERNER, T., MADIA, M., et al., “Short crack propagation analysis and fatigue strength assessment of additively manufactured materials: An application to AISI 316L”, International Journal of Fatigue, v. 151, 106396, 2021.]. (c) IBESS criteria applied by Bergant [1[1] BERGANT, M., WERNER, T., MADIA, M., et al., “Short crack propagation analysis and fatigue strength assessment of additively manufactured materials: An application to AISI 316L”, International Journal of Fatigue, v. 151, 106396, 2021.].
Figure 6.
Scanning electron microscopy (SEM) of fracture surfaces. a) fracture from a surface defect. b) whole fracture surface of specimen failing from internal defect, c) transition from striations to ductile failure. The arrows are indicating the direction of crack propagation (taken from Solberg et al. [11[11] SOLBERG, K., GUAN, S., RAZAVI, S.M.J., et al., “Fatigue of additively manufactured 316L stainless Steel: the influence of porosity and surface roughness”, Fatigue and Fracture of Engineering Materials and Structures, v. 42, pp. 2043–2052, 2019.]).
Figure 7.
Δσ-N data and curves for AM 316L. Experimental data from Solberg et al. [11[11] SOLBERG, K., GUAN, S., RAZAVI, S.M.J., et al., “Fatigue of additively manufactured 316L stainless Steel: the influence of porosity and surface roughness”, Fatigue and Fracture of Engineering Materials and Structures, v. 42, pp. 2043–2052, 2019.] and predictions reported by Bergant et al. [1[1] BERGANT, M., WERNER, T., MADIA, M., et al., “Short crack propagation analysis and fatigue strength assessment of additively manufactured materials: An application to AISI 316L”, International Journal of Fatigue, v. 151, 106396, 2021.] and carried out on the present work.
Figure 8.
K-T diagram, threshold stress range as a function of crack length. Experimental data by Andreau et al. [12[12] ANDREAU, O., PESSARD, E., KOUTIRI, I., et al., “A competition between the contour and hatching zones on the high cycle fatigue behaviour of a 316L stainless steel: analyzed using X-ray computed tomography”, Material Science and Engineering A, v. 757, pp. 146–159, 2019.], estimations carried out by Bergant et al. [1[1] BERGANT, M., WERNER, T., MADIA, M., et al., “Short crack propagation analysis and fatigue strength assessment of additively manufactured materials: An application to AISI 316L”, International Journal of Fatigue, v. 151, 106396, 2021.], and present estimations.
Figure 9.
Thresholds (experimental measured [
38[38] POURHEIDAR, A., PATRIARCA, L., MADIA, M., et al., “Progress in the measurement of the cyclic R-curve and its application to fatigue assessment”, Engineering Fracture Mechanics, v. 260, 108122, 2022.], and estimated with Eq. (
8)) for EA4T steel.
Figure 10.
Surface strain redistribution. After Abdel-Raouf et al [40[40] ABDEL-RAOUF, H., TOPPER, T.H., PLUMTREE, A., “A short fatigue crack model based on the nature of the free surface and its microstructure”, Scripta Metallurgica et Materialia, v. 25, pp. 597–602, 1991.,41[41] ABDEL-RAOUF, H., DUQUESNAY, D.L., TOPPER, T.H., et al., “Notch-size effects in fatigue based on surface strain redistribution and crack closure”, International Journal of Fatigue, v. 14, n. 1, pp. 57–62, 1992.].