Mechanical Behavior Laboratory University of Nevada, Reno

Paper

[J50] Kalnaus, S. and Jiang, Y., 2008, "Fatigue of AL6XN Stainless Steel," ASME Journal of Engineering Materials and Technology, Vol.130, 031013. doi: 10.1115/1.2931154

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Paper Abstract

Tension-compression, torsion, and axial-torsion fatigue experiments were conducted on the AL6XN alloy to experimentally investigate the cyclic plasticity behavior and the fatigue behavior. The material is found to display significant nonproportional hardening when the equivalent plastic strain amplitude is over 2x10-4. In addition, the material exhibits overall cyclic softening. Under tension-compression, the cracking plane is perpendicular to the axial loading direction regardless of the loading amplitude. The smooth strain-life curve under fully reversed tension-compression can be described by a three-parameter power equation. However, the shear strain-life curve under pure torsion loading displays a distinct plateau in the fatigue life range approximately from 20,000 to 60,000 loading cycles. The shear strain amplitude corresponding to the plateau is approximately 1.0%. When the shear strain amplitude is above 1.0% under pure shear, the material displays shear cracking. When the shear strain amplitude is below 1.0%, the material displays tensile cracking. A transition from shear cracking to tensile cracking is associated with the plateau in the shear strain-life curve. Three different multiaxial fatigue criteria were evaluated based on the experimental results on the material for the capability of the criteria to predict fatigue life and the cracking direction. Despite the difference in theory, all the three multiaxial criteria can reasonably correlate the experiments in terms of fatigue life. Since the cracking mode of the material subjected to pure torsion is a function of the loading magnitude, the prediction of cracking orientation becomes rather challenging.

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Paper Figures

Fig. 3

Fig. 3. Monotonic shear stress-shear strain curve (Download data).

Fig. 5

Fig. 5. Variation of the stress amplitude with loading cycles for the strain-controlled experiments on AL6XN: (a) tensioncompression (Download data); (b) pure torsion (Download data); (c) 90 deg out-of-phase axial-torsion (Download data).

Fig. 6

Fig. 6. Selected stress-strain hysteresis loops taken at 80% of fatigue life (Download data).

Fig. 7

Fig. 7 CSSCs (Download data).

Fig. 8

Fig. 8. Strain-life curve of AL6XN material (Download data).

Fig. 9

Fig. 9. Fatigue cracking behavior under pure torsion (Download data).

Fig. 12

Fig. 12. Base line experimental data correlated using the SWT parameter (Download data).

Fig. 13

Fig. 13. Dependence of FSK fatigue parameter on the orientation of material plane for pure torsion loading (Download data).

Fig. 14

Fig. 14. Base line experimental data correlated using the FSK parameter (Download data).

Fig. 15

Fig. 15. Fatigue life prediction of AL6XN steel based on (a) SWT model (Download data), (b) FSK model (Download data), and (c) Jiang model (Download data).

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