Fatigue and deformation behavior of thin-walled tubular specimens subjected to biaxial in-phase and out-of-phase tension-torsion constant amplitude loading in strain control and at room temperature was investigated using 1045 HR steel. The in-phase data were already available from a previous study conducted at the University of Illinois. The out-of-phase tension-torsion tests were performed with a 90 degree phase difference along both elliptical and rectangular strain paths.; Several fatigue life prediction methods were employed to correlate the experimental results including Tresca, von Mises, Zamrik's total strain parameter, Brown and Miller's critical plane approach and a proposed critical plane model. The proposed model is based on the maximum shear strain amplitude and either the maximum principal stress or the normal stress on the plane of maximum shear strain amplitude depending upon the cracking mode.; The cyclic deformation behavior of the material under proportional and nonproportional loads was also investigated employing both the Tresca and von Mises yield criteria. The additional cyclic hardening developed under nonproportional loading and its dependence on the strain-range and the ratio of torsional to axial strain amplitudes is also discussed.
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