Many experiments have indicated the dependence of strength as well as damage and fracture behavior of anisotropic ductile metals on loading direction and on stress state. To predict safety and lifetime of structures in a realistic manner these effects must be taken into account in constitutive models and corresponding numerical analysis.
In the presentation the influence of stress state and loading direction with respect to the principal axes of anisotropy on damage and fracture behavior of the anisotropic aluminium alloy EN AW-2017A is investigated. New experiments with biaxially loaded specimens and corresponding numerical simulations have been performed. Series of forces with different load ratios act on the X0- and the H-specimen leading to different damage and failure mechanisms. Digital image correlation is used to monitor evolution of strain fields in critical parts of the specimens. Failure modes on fracture surfaces are visualized by scanning electron microscopy. Stress states are predicted by numerical simulation of the specimens and are used to explain damage and fracture processes on the micro-level. The results have shown that the stress state, the load ratio and the loading direction with respect to the principal axes of anisotropy have an influence on the width and the orientation of localized strain fields as well as on the formation of damage processes and fracture modes on the micro-scale. Therefore, the enhanced experimental program with biaxially loaded specimens considering different loading directions and load ratios is recommended for characterization of anisotropic ductile metals.
Magnesium alloys with their high specific strength and low weight are used as structural materials in different applications. They have suitable mechanical properties and excellent damping. Magnesium-wrought alloys, such as for instant AZ31, are needed for applications where their weight is important. It is well-known that the mechanical properties of Mg alloys depend very strongly on their microstructure and texture. Grain refinement is an effective way to achieve higher strength and ductility.
Magnesium alloys and composites were prepared using various methods of severe plastic deformation - accumulative roll bonding (ARB), rotary swaging (RSW), equal-channel angular pressing (ECAP), and hot extrusion (HE). Mechanical characteristics were estimated at temperatures from room temperature up to 300 °C. Plastic anisotropy and tension-compression asymmetry were estimated for deformation temperatures up to 200 °C. The amplitude-dependent internal friction was measured at room temperature. Anelastic planar anisotropy of internal friction was observed. Thermal properties of samples prepared with ARB and ECAP processing. The CTE of sheets prepared by ARB processing exhibit planar anisotropy. The CTE decreases with an increase in ARB passes while the thermal conductivity increases.
Observed effects are closely linked to the developed texture of materials and deformation mechanisms: twinning and dislocation slip in non-basal planes.