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SUMMARY:Magnesium alloys microstructures: coupling experiments and simulat
 ions - Dr Antoine Jerusalem\,  University of Oxford
DTSTART:20130503T130000Z
DTEND:20130503T140000Z
UID:TALK45001@talks.cam.ac.uk
CONTACT:Ms Helen Gardner
DESCRIPTION:Lightweight Mg alloys constitute alternative materials of inte
 rest for many industrial sectors and in particular the transport industry.
  Indeed\, reducing vehicle weight and thus fuel consumption can actively b
 enefit the global efforts of the current environmental industry policies. 
 Despite being already widely used\, high-pressure die-casting and wrought 
 alloys are still subject to intense research campaigns. The micromechanics
  of deformation in both type of alloys are still not fully understood and 
 neither simulations alone or experiments alone can possibly unravel the re
 maining unkowns. In this presentation\, two approaches will be presented m
 aking use of a coupled experimental-modeling approach:\n\n1-Casting proces
 ses usually lead to the formation of significant amounts of gas and shrink
 age microporosity\, which adversely affects the mechanical properties. The
  application of hydrostatic pressure after casting can reduce the porosity
  and improve the properties but little is known about the effects on the s
 ize and morphology of the casting pores. In the present study we have used
  an experimental-computational approach based on X-ray Computed Tomography
 \, image analysis and finite element analysis for the determination of the
  3D porosity distribution and its evolution with hydrostatic pressure in a
  high pressure die-cast AZ91 Mg alloy. The corresponding reconstructed 3D 
 pore distribution has been used as an input for finite element simulations
 \, thus complementing experiments with numerical data difficultly accessib
 le otherwise.\n\n2-Wrought Mg alloys present strong textures and thus spec
 ific deformation mechanisms are preferentially activated depending on the 
 orientation of the applied load. Developing models that can contemplate th
 e complexity inherent to deformation of Mg alloys is now timely. In partic
 ular\, a comprehensive crystal plasticity model including both twin and sl
 ip systems as well as their interactions through hardening mechanisms prov
 ides a numerical tool directly relating texture and deformation mechanisms
 . Here\, a crystal plasticity finite element model previously developed ha
 s been expanded to represent more realistic polycrystal features consideri
 ng the topological information of grains. In this new model\, a 3D polycry
 stal is represented as a 3D Voronoi tessellation\, thus allowing for the s
 tudy of the local intragranular mechanical fields\, as well as the specifi
 c interactions between twin nucleation/propagation\, and the accompanying 
 slip systems. The experimental calibration and validation of the model are
  ultimately carried out with an AZ31 rolled sheet\, along with quantitativ
 e 2D and 3D EBSD characterization of the evolution of deformation twinning
 . Ultimately\, the model demonstrates its ability at capturing some of the
  intrinsic micromechanisms associated to twin nucleation\, growth and tran
 smission.
LOCATION:Oatley Seminar Room\, Department of Engineering
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