The effect of phase continuity on the fatigue and crack closure behavior of a dual-phase steel |
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Authors: | R M Ramage K V Jata G J Shiflet E A Starke |
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Affiliation: | (1) Department of Materials Science, University of Virginia, Thornton Hall, 22901 Charlottesville, VA |
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Abstract: | The effect of phase continuity on the low cycle fatigue and fatigue crack growth behavior of a Fe-C-Mn dual-phase steel has
been investigated. Two microstructures, one consisting of continuous ferrite and the other continuous martensite, were examined.
Although there was no difference in the low cycle fatigue lives between the two microstructures, the continuous martensite
structure exhibited an extremely high fatigue threshold value of 20 MPa m1/2, compared to 16 MPa m1/2 for the continuous ferrite microstructure. A major effect of phase continuity has also been found in the crack closure levels
during fatigue crack propagation studied over three decades of crack growth rates. The continuous martensite microstructure
exhibited much higher closure levels due to the martensite constraining the plastic deformation in the ferrite and bearing
a larger portion of the applied cyclic load. This effect is similar to the extrinsic toughening phenomenon cited in the literature.
After accounting for the closure levels the intrinsic or effective fatigue crack growth rates are similar for the two microstructures.
These intrinsic thresholds are predicted by employing experimentally obtained low cycle fatigue parameters and the ferrite
grain size. |
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