XFEM Analysis of Strain Localization on Hostun RF Sand using Integral Type Nonlocal Model


Meysam Zarinfar

PhD Candidate, Civil Engineering Department
K.N.Toosi University of Technology, Tehran, Iran
Corresponding author; e-mail: zarinfar@dena.kntu.ac.ir

Farzin Kalantary

Assistant Professor, Civil Engineering Department
K.N.Toosi University of Technology, Tehran, Iran
e-mail: fz_kalantary@yahoo.co.uk



Localization phenomena, as e.g. shear bands, is a narrow zone of local concentrations of plastic strains. The numerical methods that use the classical continuum models, suffer from the excessive mesh dependence when a strain-softening model is used. With a nonlocal formulation, this pathology is eliminated. In the present paper, a new relation was proposed to calculate the stress rate based on the integral-type nonlocal model. For nonlocal plasticity, element size had a critical effect on the solution. Sufficiently refined meshes were required for an accurate solution without mesh dependency. It was shown that an extended finite element method can be applied to the problem to decrease the required mesh density close to the localization band. A new method based on the local bifurcation theory was proposed for the initiation and growth criterion of the strain localization interface. Localization of deformation in biaxial tests on Hostun Rf sand were used to demonstrate the efficiency of the mixed XFEM–integral type nonlocal model in shear band localization modeling without mesh dependency. It was shown that shear banding can take place in both contractive and dilative specimens. Findings concerning the occurrence and progression of strain localization were discussed. Attention was laid on the influence of the mean effective stress and shear band orientation.

Keywords: XFEM, Nonlocal plasticity, Shear band orientation, Mean effective stress, Biaxial tests

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