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Item type:Publication, Access status: with files , Mechanical characterisation and constitutive modelling of wrought magnesium sheets exhibiting tension-compression asymmetry(2017); Wrought magnesium alloys have emerged as promising candidates for highly loaded structural components in the automobile industry recently, due to their high specific strength and low density. In this work, two aspects of wrought magnesium alloys are studied experimentally and computationally: the mechanism-based modelling of plastic deformation and the crashworthiness assessment of simple structures. A constitutive model was developed to capture the plastic behaviour of wrought magnesium sheets under monotonic loading. Wrought magnesium sheets exhibit a strong and evolving tension compression asymmetry in terms of flow stress and r-value (strain anisotropy parameter). A yield function originally proposed by Cazacu, Plunkett and Barlat in 2006 was extended by introducing a new parameter depending on the plastic multiplier to describe this tension-compression asymmetry and its evolution. The model was applied to two different magnesium wrought alloys, AZ31 (Mg+3%Al+1%Zn) and ZE10 (Mg+1%Zn+0.3%Ce), each produced as rolled sheet and as extruded profile. A series of mechanical tests including uniaxial tensile and compression tests along different orientations, through thickness compression tests, shear tests, and notched bar tests was conducted for characterising the mechanical behaviour under various stress states. Experimental results confirm significantly different plastic deformation behaviour of the two alloys, which were resulted from their respective initial textures. For calibration of the material model, identification of material parameters was accomplished with the experimental data based on an error minimisation scheme. The computational results show that the proposed model captures the tension- compression asymmetry of both alloys. The calibrated model was finally applied to a pure bending simulation. The good agreement between the simulated and the semi-analytically calculated bending moment-curvature diagram demonstrates the predictive capability of the present model for the considered magnesium alloys. Experimental study and numerical simulations were conducted to investigate the plastic buckling and crush behaviour of structural components with hollow rectangular profiles fabricated from the two magnesium alloys. The used modelling approach is justified by balancing achievable accuracy and computational efforts. The performance of the components made by magnesium alloys was evaluated in term of the dissipated specific energy in the crush tests and compared with respective aluminium components. It is revealed that the observed high dissipation of magnesium alloys during crushing is related to the work hardening behaviour in compression.Publicationtype: Doctoral Thesis469 1325 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Crashworthiness of magnesium sheet structures(Trans Tech Publications, 2013-07); ; ; ; A hollow rectangular profile, as an example of a typical structural component made of magnesium alloy sheets has been built, tested and evaluated in order to assess its behaviour during axial crushing. The profiles were joined from plane sheets of AZ31 and ZE10, respectively, by laser beam welding and were then tested in compression. Numerical simulations have been conducted to understand the complex interplay between hardening characteristics of the materials under investigation, profile cross-section variation and energy absorption. The results from the compression testing of the profiles show that the welds are not the source of damage initiation and failure. The performance of the magnesium profiles in terms of dissipated specific energy is confirmed for small and intermediate displacements to be comparable to that of aluminium profiles. For large displacements, however, the shear-type failure mode of magnesium causes a sharp drop of the crushing force and thus limits the energy absorption. These findings demonstrate the requirement for an alloy and wrought magnesium process development specifically for crash applications which aims at progressive hardening along with high ductility for improving the bending and shear behaviour.Publicationtype: Conference Paper264