ESR5 Maria Lazari

Research project description

FEM regularization for post localized bifurcation in fluid saturated media

Fellow:                  Maria Lazari (ESR5)

Institution:             Department of Civil, Architectural and Environmental Engineering, University of Padua (UNIPD), Italy

Supervisors:          Prof. Bernhard A. Schrefler, Dr. Ing. Lorenzo Sanavia

 

Localization of deformation into shear bands is one of the most interesting bifurcation problems in solid mechanics as it is considered to be the precursor of failure. Recently, an increasing interest focuses on strain localization problems of multiphase porous media due to the importance of coupling the solid deformation with the pore-fluid flow in practical engineering.

In case of material which exhibits softening, the numerical simulation of shear bands with classical theories of plasticity breaks down in the post-bifurcation regime where the rate boundary value problem becomes ill-posed. Subsequently, the numerical solutions suffer from pathological dependence on spatial discretization resulting in excessive mesh sensitivity.

The main objective of this project is the implementation of regularized constitutive models, to avoid the mesh sensitivity problem in localization simulation of multiphase materials. Viscoplasticity and nonlocal theories will be adopted as regularization techniques in the post bifurcation regime. The effectiveness of these theories, in case of granular soils, will be explored by simulation of an impact biaxial test and a quasi-static slope stability problem.

In the context of the overall project, this thesis has as an ultimate goal to provide a realistic description of the initiation of rainfall-induced landslides, using the constitutive model for unsaturated soils developed by Aleksandra Jakubczyk (ESR1 fellow). Concerning the cooperation with other Mumolade fellows, it is noted that the regularized model which will be developed in the framework of this research will be provided to Evanthia Kakogiannou (ESR4 fellow) for the sake of objectivity of her numerical results.

                      

Figure: (a) Plane strain biaxial test on Hostun RFsand (Mokni & Desrues, 1998), (b) Equivalent plastic strains for elastoplastic and elasto-viscoplastic (with viscosity ?=10 sec) constitutive model of a plane

strain localization simulation.