An experimental–numerical method to determine the work-hardening of anisotropic ductile materials at large strains

• Uniaxial tension tests performed on a series of Al 6xxx alloy family specimens.
• Laser gauge used for precise measurements of specimen diameter after necking.
• Crystal plasticity model used to estimate the anisotropic yield surface of the material.
• FE model with anisotropic plasticity used to simulate after necking behaviour.
• Equivalent stress up to fracture found from calibration of the FE model vs. the experimental data.

The determination of work-hardening for ductile materials at large strains is difficult to perform in the framework of usual tensile tests because of the geometrical instability and necking in the specimen at relatively low strains. In this study, we propose a combination of experimental and numerical techniques to overcome this difficulty. Extruded aluminium alloys are used as a case since they exhibit marked plastic anisotropy. In the experiments, the minimum diameters of the axisymmetric tensile specimen in two normal directions are measured at high frequency by a laser gauge in the necking area together with the corresponding force, and the true stress–strain curve is found. The anisotropy of the material is determined from its crystallographic texture using the crystal plasticity theory. This data is used to represent the specimen by a 3D finite element model with phenomenological anisotropic plasticity. The experimental true stress–strain curve is then used as a target curve in an optimisation procedure for calibrating the hardening parameters of the material model. As a result, the equivalent stress–strain curve of the material up to fracture is obtained.