NUMERICAL SIMULATIONS OF DUCTILE FAILURE IN EXTRUDED ALUMINIUM ALLOYS USING A COUPLED MODEL OF ELASTO-PLASTICITY AND DAMAGE

A test programme has been carried out to establish the mechanical properties of three extruded aluminium alloys. The investigated alloys exhibited significant anisotropy in strength, plastic flow and ductility. The anisotropy is mainly due to crystallographic texture, and an anisotropic yield criterion is needed to describe the mechanical behaviour. Several yield criteria were evaluated against the experimental data. The yield criterion Yld96 proposed by Barlat and co-workers was found to be superior with respect to accuracy for the actual aluminium alloys. In an attempt to model ductile failure of the investigated materials, a coupled model of elasto-plasticity and ductile damage was implemented in LS-DYNA for plane stress analysis with corotational shell elements. The material model combines the anisotropic yield criterion Yld96 with the associated flow rule, isotropic strain hardening and isotropic damage. The parameters defining the yield criterion and the strain hardening were determined from tensile tests and pure bending tests, while the damage parameters were identified using inverse modelling of tensile tests performed with purpose-made specimens. A series of biaxial tensile tests was also completed, and the results from these tests were used in an attempt to evaluate the constitutive model.