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Numerical aspects of non-local viscoplasticity

This work demonstrates the applicability of the non-local concept on strain localization analysis within the framework of multiphase porous media. A non-local model of integral-type is used in conjunction with viscosity as an extension of an already available viscoplastic Drucker-Prager model with non-associated flow rule [5]. This coupling allows for eliminating mesh dependency in strain localization even in case of weakly rate-sensitive materials (i.e. dense sand) where viscoplasticity is not sufficient to suit numerical requirements.

Following the approach proposed in [1], in non-local application the viscous nucleus is replaced by an average viscous nucleus (non–local counterpart) over the volume of the structure. When the so-called internal length approaches zero, the local viscoplastic model is regained. The model has been implemented in the finite element code COMES-GEO [2;3;4;6;7;8], allowing for non-local extension to more sophisticated yield criteria only by minor modifications.

The efficiency of the model in terms of regularized performance is illustrated using benchmark numerical examples from the geomechanics field. Attention is paid to the interaction between the characteristic lengths introduced by non-locality and viscosity. In this context a parametric sensitivity analysis is conducted and the results highlight the influence of such a coupling on the numerical predictions.

REFERENCES

[1]di Prisco, C., Imposimato, S. and Aifantis, E.C. A viscoplastic constitutive model for granular soils modified according to non-local and gradient approaches. International Journal for Numerical and Analytical Methods in Geomechanics (2002) 26:121–138.
[2]Gawin, D. and Schrefler, B.A. Thermo-hydro-mechanical analysis of partially saturated. Engineering Computations (1996) 13(7):113-143.
[3]Gawin, D. and Sanavia, L. A unified approach to numerical modelling of fully and partially saturated porous materials by considering air dissolved in water. CMES-Comp. Model. Eng. Sci. (2009) 53:255-302.
[4]Gawin, D. and Sanavia, L. Simulation of cavitation in water saturated porous media considering effects of dissolved air. Transport Porous Med (2010) 81:141-160.
[5]Lazari, M., Sanavia, L. and Schrefler, B.A. Viscoplastic regularization of strain localization in fluid-saturated porous media, Proceedings of WCCM XI-ECCM V, Tomo IV: 3495-3503, Barcelona, (2014), ISBN: 978-84-942844-7-2.
[6]Lewis, R.W. and Schrefler, B.A. The Finite Element Method in the Static and Dynamic Deformation and Consolidation of Porous Media, Wiley and Sons, Chichester, (1998).
[7]Sanavia, L., Pesavento, F. and Schrefler, B.A. Finite element analysis of non-isothermal multiphase geomaterials with application to strain localization simulation. Comput. Mech. (2006) 37:331-348.
[8]Sanavia, L., François, B., Bortolotto, R., Luison, L. and Laloui L. Finite element modelling of thermo-elasto-plastic water saturated porous materials. Journal of Theoretical and Applied Mechanics (2008) 38:7-24.

Author(s):

Maria Lazari    
University of Padua
Italy

Lorenzo Sanavia    
University of Padua
Italy

Bernhard A. Schrefler    
University of Padua
Italy