The Evolution of Subsequent Yield Loci with Finite Plastic Deformation Under Proportional and Non-Proportional Loading Paths in annealed AA6061-T6 aluminum alloy, and annealed and as-received AZ31 magnesium alloys.
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This investigation reports for the first time, the subsequent yield loci after finite plastic deformation based on 10µ? offset definition yield, of an annealed A6061-T6 aluminum alloy, as-received extruded AZ31 magnesium alloy and annealed extruded AZ31 magnesium alloy under proportional and non?proportional loading paths. The proportional loading paths comprise of uniaxial tension, free end torsion, and combined tension-torsion radial (proportional) loading paths. The tension loading followed by torsion, and torsion followed by tension are the non-proportional loading paths. Each subsequent locus, in case of proportional loading paths, shows a very well-known shape of being nearly flat in reverse direction and having a prominent “nose” in the loading direction that deviates substantially from a generalized isotropic behavior. Further, a rapid evolution of the mixed hardening effect in annealed AA6061-T6 aluminum alloy is observed. Differences associated with the path-dependent effects are seen in the non-proportional yield loci in this alloy. Subsequent yield loci for as-received and annealed AZ31 magnesium alloy under proportional loading paths show a prominent nose in the loading direction and an almost flat region in the reverse loading direction with evolution of significant isotropic hardening under tension, and visible kinematic hardening under torsion loading path. Strong path-dependency is noticed in subsequent yield loci under non-proportional loading directions along with hardening effects for AZ31 alloys. All the yield loci are investigated in tension?torsion (?????3???) stress space. The results are significantly different than observed for other metals, especially for aluminum alloys (e.g. Khan et al., 2009). Elastic moduli within each subsequent yield loci are also measured during these experiments with the increase in plastic strain. The observed small reduction in the elastic moduli with increasing plastic strains are very similar to the ones reported in earlier studies by Khan et al., (2009; 2010).