The crystal plasticity theory predicts that hardening on a particular slip system and its corresponding work-hardening rate will depend on the slip activity on both this slip system and all others. The exact form of this dependence is defined by the latent hardening description in form of the latent hardening matrix or the interaction matrix. It has been assumed that this matrix describes the relative strength of various dislocation interactions and is therefore the same for a wide range of alloys with the same lattice structure. Different methods have been used to estimate the values of the interaction matrix components: one is experimental and uses strain-path changes; another simulates the dislocations dynamics in a crystal directly at the microscale and estimates the strength of the forming locks. In this work, the influence of the interaction matrix (and thus latent hardening) on the development of plastic anisotropy is studied. An extruded AA6060 alloy is tested in uniaxial tension in different directions and the anisotropy of the alloy is found to evolve considerably throughout the deformation. A crystal plasticity model is used to simulate the experimental tests, and the use of different interaction matrices is evaluated. A noticeable influence on the predicted evolution of plastic anisotropy as well as the stress-strain field and slip inside the constituent grains is found.

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 optimization 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.

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A model of a polycrystalline material is studied, where each grain consists of several zones with different plastic properties. The size and configuration of the zones as well as their properties are mimicking the situation inside the crystals of artificially aged Al alloys with precipitate free zones (PFZs). The properties of the different zones are conjectured based on micromechanical models and experimental observations of the AA6000 series of Al alloys. A periodic patch of such a composite material, subjected to plane-strain tension, is modelled using the finite element method. The material behaviour is described by a single crystal plasticity model. The results of the simulations show a number of characteristic features emerging in composite material systems, including sliding and distortion of grain boundaries and shear band formation at grain boundary triple points. The assumptions made about the properties of the different zones in the crystals are evaluated. The distributions of plastic strain and deviatoric and hydrostatic stresses in the composite crystalline systems are discussed.

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