A constitutive model for a uranium-niobium alloy

A constitutive model that includes the effects of elasticity, crystal reorientation (twinning or detwinning), phase transformations, and plasticity is presented. The model is applied to a uranium 6 wt % niobium (U-6Nb) alloy, which is known to exhibit the shape memory effect. The inelastic strains for phase transformation and reorientation are based on the material's phase diagrams. The model captures the effects of martensitic transformation and reorientation; both of the phenomena are coupled with the alloy's phase diagrams, which are defined in terms of temperature, hydrostatic pressure, and shear stress. Computational simulations are presented that demonstrate the ability of the model to capture the relevant physical response of the material. Also, we include experimental results that demonstrate the phenomena of phase transformation, reorientation, and plasticity for low- and high-strain rates and for variations in temperature. The model replicates the experimental data for the broad range of strain rates and temperatures. Comparisons between the model and low-strain rate data, which demonstrate the shape memory effect of U-6Nb, are also provided.