Modelling of plastic anisotropy in heat-treated aluminium extrusions

Uniaxial tensile tests have been conducted for the commercial aluminium alloy AA7108 in different tempers. In addition, pure bending tests were performed for temper W (20 min). The influence of heat-treatment on plastic anisotropy in strength, plastic flow and strain hardening has been investigated by performing tests with three loading directions with respect to the extrusion axis. The experimental data have been used to determine a constitutive model for the alloy. The plastic anisotropy is described by the Yld96 yield criterion of Barlat and co-workers, while the strain hardening is defined by a non-linear isotropic strain hardening rule. It is found that the plastic anisotropy (i.e. variation in yield strength and R-ratio with direction) is affected by the temper condition, but identical shape of the yield surface can be used for all tempers with reasonable accuracy. The variation in strength and strain hardening with heat-treatment is accounted for calibration of the non-linear isotropic hardening rule.