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Research Papers

Fatigue of AL6XN Stainless Steel

[+] Author and Article Information
Sergiy Kalnaus

Department of Mechanical Engineering (312), University of Nevada Reno, Reno, NV 89557

Yanyao Jiang1

Department of Mechanical Engineering (312), University of Nevada Reno, Reno, NV 89557yjiang@unr.edu

1

Corresponding author.

J. Eng. Mater. Technol 130(3), 031013 (Jun 11, 2008) (12 pages) doi:10.1115/1.2931154 History: Received August 22, 2007; Revised January 02, 2008; Published June 11, 2008

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 2×104. 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.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Three-dimensional view of the microstructure of the AL6XN stainless steel. Magnification: ×800. Etching: V2A, room temperature.

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Figure 2

Specimens used in fatigue experiments (all dimensions are in mm): (a) tension-compression specimen; (b) solid shaft specimen; (c) tubular specimen

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Figure 3

Monotonic shear stress-shear strain curve

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Figure 4

Schematics of the loading paths

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Figure 5

Variation of the stress amplitude with loading cycles for the strain-controlled experiments on AL6XN: (a) tension-compression; (b) pure torsion; (c) 90deg out-of-phase axial-torsion

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Figure 6

Selected stress-strain hysteresis loops taken at 80% of fatigue life

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Figure 8

Strain-life curve of AL6XN material

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Figure 9

Fatigue cracking behavior under pure torsion

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Figure 10

Fatigue cracking behavior: (a) shear cracking; (b) tensile cracking; (c) mixed cracking

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Figure 11

Crack propagation through the thickness of the specimen

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Figure 12

Base line experimental data correlated using the SWT parameter

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Figure 13

Dependence of FSK fatigue parameter on the orientation of material plane for pure torsion loading

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Figure 14

Base line experimental data correlated using the FSK parameter

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Figure 15

Fatigue life prediction of AL6XN steel based on (a) SWT model, (b) FSK model, and (c) Jiang model

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Figure 16

Comparison between observed and predicted orientations of fatigue cracks based on (a) SWT model, (b) FSK model, and (c) Jiang model

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Figure 17

Prediction of cracking orientation using the Jiang model: (a) pure torsion Δγ∕2=1.2%; (b) pure torsion Δγ∕2=0.86%; (c) 90deg out-of-phase axial-torsion Δε∕2=0.32%, Δγ∕2=0.55%

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