Stress-regime-dependence of inelastic anisotropy in forged age-hardening aluminium alloys at elevated temperature: Constitutive modeling, identification and validation

Many structural materials exhibit stress-regime-dependent anisotropy of inelastic responses. Examples are age-hardening aluminium alloys forgings. Experimental creep curves indicate that inelastic strain rates depend significantly on the loading direction within the power law regime, while in the power law breakdown range the anisotropy is weak and can be neglected. The aim of this paper is to analyze anisotropic behavior of forged AA2014 alloy and to develop a constitutive model to describe inelastic response under multi-axial stress state. Microstructural observations suggest that the anisotropy is primarily caused by elongated grains and coarse particles on grain boundaries. To account for inhomogeneous inelastic deformation and stress redistribution in different microstructural zones a composite model is developed. Constitutive equations for inelastic-hard and inelastic-soft constituents and anisotropic rules for mechanical interactions between them are elaborated. Hardening/recovery and overageing processes in grain interiors are characterized by internal state variables and kinetic equations. The model is calibrated against families of creep curves for two loading directions in a wide stress and temperature ranges. For the validation, creep tests under the loading with the angle of 30 degrees relative to the longitudinal grain axis as well as tensile tests are simulated by the model and results are compared with experimental data.