Results of nonproportional stress changes on creep and plastic strains resulting from abrupt changes in proportion of tension and torsion are reported. Both step-up and step-down changes are included. Constitutive equations based on data for single step creep and recovery tests previously reported are used to describe the test results. A viscous-viscoelastic model with aging effects and modifications for step-down tests predicted the creep behavior reasonably well. The prediction of time-independent plastic strains is also described.

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