[SIO GP Seminars] Seminar TOMORROW - Tues. 12:30pm Ricardo A. Lebensohn

[Leah Ziegler]

Join us for this week's Geophysics Seminar held TOMORROW (Tuesday)  
instead of the usual Friday:

  ========================

Tuesday, Dec. 5, 12:30 PM
   (refreshments served)
   Munk Conference Room

Ricardo A. Lebensohn
Los Alamos National Lab

   "Towards improved multiscale modelling of viscoplastic  
geomaterials: full-field and statistical approaches at the mesoscale"

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Abstract:

> Multiscale modelling of plastically-deforming geomaterials has been  
> an active field of research over the past 20 years. One goal of  
> these models was to obtain accurate predictions of lattice  
> preferred orientation (LPO) associated with viscoplastic flow at  
> different locations of some portion of the earth's interior and, in  
> turn, correlate these local LPOs with elastic wave propagation. The  
> success of these multiscale approaches essentially depends on: a)  
> an adequate Finite Element analysis at the macroscale, based on  
> realistic boundary conditions and driving forces, and b) the  
> accuracy of the adopted polycrystal model (i.e. at the mesoscale)  
> to account for LPO and microstructure evolution during viscoplastic  
> flow, based on the knowledge of the single crystal deformation  
> mechanisms (i.e. at the microscale). In this talk we will focus on  
> recent improvements of the micromechanical modelling at the mesoscale.
>
> In the first part we will present a numerical formulation based on  
> Fast Fourier Transforms to obtain the micromechanical fields in  
> plastically-deformed 3-D polycrystals. This formulation, developed  
> in the last decade as a fast algorithm to compute the elastic and  
> elastoplastic response of composites using as input a digital image  
> of their microstructures and, in turn, adapted to deal with 3-D  
> polycrystals deforming by dislocation glide, provides an exact  
> solution of the governing equations, has better performance than a  
> small-scale Finite Element calculation for the same purpose and  
> resolution, and can use voxelized microstructure data as direct  
> input. To illustrate the capabilities of this model, we will  
> compare its predictions with experimental results on effective  
> properties, local fields, subgrain structure formation, and local  
> LPO evolution in metallic and geological materials. Next, we will  
> introduce several nonlinear homogenization formulations for  
> viscoplastic polycrystals and, for validation, we will compare  
> their predictions with ensemble averages of FFT-based full-field  
> solutions. We will then show examples of the use of these nonlinear  
> homogenization schemes in multicale calculations to account for  
> anisotropy effects in metallic systems. Implications of these  
> recent developments to multiscale modelling of geomaterial systems  
> will be finally discussed.
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