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Amir R. Khoei

                                                (To download a complete list of Publications click here)

 

 

Research interests

Computational Nano-mechanics

Computational plasticity (FEM, X_FEM and Meshless methods)

Computational Fracture Mechanics

Computational Soil Mechanics

Large deformation analysis

Error estimation and adaptivity for plasticity problems

Contact and frictional modelling

Strain localization analysis

 

 

Computational Nano-Mechanics

The purpose of research activities in computational nano-mechanics is to investigate the characteristics of the material at nano-scale. The current research is based on the Molecular Dynamics simulations and the non-linear finite element simulations using the Cauchy-Born hypothesis. Molecular Dynamics simulation is used as a standard tool in computational nano-mechanics. The research is conducted by developing a Molecular Dynamics software which is able to simulate multi-particle systems in canonical and micro-canonical ensembles. Furthermore, a novel multi-scale approach is developed for modeling of the surface effect in crystalline nano-structures. The technique is based on the Cauchy-Born hypothesis in which the strain energy density of equivalent continua is calculated by means of inter-atomic potentials.

(a)(b)(c)(d)

A concurrent multi-scale modeling of a nano-scaled plate comprising random inhomogeneities; a) molecular dynamics model, b) stress contour using MD model, c) multi-scale model, d) stress contour using multi-scale model (see: Mechanics of Materials, 83, 40-65, 2015)

(a)(b)

A hierarchical multi-scale modeling of a nano-scale beam subjected to thermo-mechanical loading; a) molecular dynamics and multi-scale models, b) stress contours using molecular dynamics and multi-scale models (see: International Journal for Numerical Methods in Engineering, 97, 79-110, 2014)

 

 

Computational Fracture Mechanics

A comprehensive research work has been performed on fracture mechanics with special regards to crack growth and crack propagation in the brittle, cohesive and ductile materials. The numerical simulations are based on the adaptive FEM analysis and the X-FEM technique, which have been verified by the results of experimental tests. The method of adaptive finite element procedure is used to refine the mesh at the crack tip region based on the estimated error. The simulation of crack propagation was performed in 2D and 3D problems for both the elastic crack growth and the damage-plastic crack propagation. The other technique is based on the extended-FEM method, which is a state-of-the-art computational approach in FEM, and eliminates the necessity of using mesh generators in the analysis of continuum mechanics problems involving any kind of interfaces, such as bi-materials, contact problems, and fractured media.

(a) (b) (c)

The crack trajectory for a plate with two holes; a) X-FEM technique, b) adaptive FEM method, c) von-Mises stress contour (see A.R. Khoei, Extended Finite Element Method, Theory and Applications, John Wiley, 2015)

 

 

Computational Continuum Mechanics

The main area of research in computational solid mechanics encompasses large deformations, plasticity behaviour and contact problems for various solid mechanics including: metal forming applications and shear band localization problems. Both classical and Cosserat continuum mechanics have been employed in the framework of FEM analysis, adaptive FEM simulation, meshless technique, X-FEM modeling, and ALE formulation. Recent achievements in computational modeling of large plastic deformations are based on a three-invariant cap plasticity model and an enriched arbitrary Lagrangian-Eulerian finite element technique. A generalized cap plasticity with the isotropic-kinematic hardening rule is developed within the framework of an enriched arbitrary Lagrangian-Eulerian FE formulation. An enriched finite element method is implemented based on the extended FEM technique to capture the arbitrary interfaces independent of element boundaries. The process is accomplished by performing a splitting operator to separate the material (Lagrangian) phase from convective (Eulerian) phase, and partitioning the Lagrangian and relocated meshes with some sub-quadrilaterals whose Gauss points are used for integration of the domain of elements. The enriched ALE-FEM technique is applied to simulate the friction between two bodies by imposing the contact constraints and modifying the contact properties of frictional slip through the node-to-surface contact algorithm in the concept of penalty and augmented-Lagrange approaches.

The normal contact-impact of two elastic rings; The deformed configurations at various time steps (see: Computer Methods in Applied Mechanics and Engineering, 269, 198-221, 2014)

 

 

Computational Geomechanics

Research activities in computational geotechniques have been developed based on the FEM and X-FEM modeling of deforming porous medium interacting with the flow of two immiscible wetting and non-wetting pore fluids. The governing equations are derived for unsaturated soils, such as the earth and rockfill dams, within the framework of the generalized Biot's theory. An integrated software environment is designed for multi-disciplinary computational modeling of geotechnical problems, called SUT-DAM (Advances Engineering Software, 37, 728-753, 2006.). The SUT-DAM is designed in both popularity and functionality with the development of user-friendly pre- and post-processing software. In SUT-DAM, a numerical model is developed based on a Lagrangian finite element formulation for large deformation dynamic analysis of saturated and partially saturated soils. An adaptive FEM strategy is used into the large displacement finite element formulation by employing an error estimator, adaptive mesh refinement, and data transfer operator. The SUT-DAM supports different yield criteria, including classical and advanced constitutive models, such as the Pastor-Zienkiewicz and cap plasticity models.

A hydraulically-driven fracture propagation in an infinite porous media (see: International Journal of Fracture, 188, 79-108, 2014)

 

 

Software Design

SUT_DAM (version 4.0)  

An integrated software environment for geotechnical engineering

For more information about the software see the following paper:

A.R. Khoei, S.A. Gharehbaghi, A.R. Azami and A.R. Tabarraie,

SUT-DAM: An integrated software environment for multi-disciplinary geotechnical engineering,

Advances Engineering Software, 37, 728-753, 2006.

 

 

 
                                           Copyright Civil Engineering Department, Dr. AR Khoei, January 2015, For more information email: arkhoei@sharif.edu