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strain-softening
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H-adaptive finite element analysis for localization phenomena with reference to metal powder forming
, Article Finite Elements in Analysis and Design ; Volume 38, Issue 6 , 2002 , Pages 503-519 ; 0168874X (ISSN) ; Lewis, R. W ; Sharif University of Technology
2002
Abstract
Standard finite element models, i.e. finite element methods that use standard constitutive models, suffer from excessive mesh dependence when strain-softening models are used in numerical analyses and cannot reproduce the size effect commonly observed in quasi-brittle failure. In this paper, an h-adaptive analysis for the mixed finite element solution of solid mechanics problems is presented with special reference to metal powder forming involving localization due to material instability. A remeshing strategy is employed to compute the distribution of required element size using the estimated error distribution. The numerical results are obtained for a Von-Mises yield criterion applied to a...
An enriched-FEM model for simulation of localization phenomenon in Cosserat continuum theory
, Article Computational Materials Science ; Volume 44, Issue 2 , December , 2008 , Pages 733-749 ; 09270256 (ISSN) ; Karimi, K ; Sharif University of Technology
2008
Abstract
The standard finite element models, i.e. the finite element methods that use the classical continuum models, suffer from the excessive mesh dependence when a strain-softening model is used. It cannot converge to a meaningful solution and the governing differential equation loses the ellipticity. This paper presents an enriched finite element algorithm for simulation of localization phenomenon using a higher order continuum model based on the Cosserat continuum theory. The governing equations are regularized by adding the rotational degrees-of-freedom to the conventional degrees-of-freedom and including the internal length parameter in the model. The extended finite element method (X-FEM) is...
Geotechnical characterization and collapsibility of a natural dispersive loess
, Article Engineering Geology ; Volume 250 , 2019 , Pages 89-100 ; 00137952 (ISSN) ; Kiani, M ; Sadeghi, M ; Jafarzadeh, F ; Sharif University of Technology
Elsevier B.V
2019
Abstract
During preliminary investigation phase of the national Chabahar-Zahedan railway line, serious geotechnical problems including non-uniform settlements, tensile cracks, and local collapse were reported in parts of the path near the coastline. A follow-up field investigation revealed that the in-situ soil at construction site has a metastable structure being sensitive to saturation and loading. Therefore, a comprehensive series of physical, chemical, electro-chemical, and geotechnical tests were conducted to classify and characterize the soil properties and behavior in its natural state. The natural soil was classified as a clayey loess with moderately dispersive to dispersive characteristics....
New method in characterizing tensile softenig procedure in concrete
, Article ISEC 2011 - 6th International Structural Engineering and Construction Conference: Modern Methods and Advances in Structural Engineering and Construction, 21 June 2011 through 26 June 2011 ; June , 2011 , Pages 1145-1150 ; 9789810879204 (ISBN) ; Mofid, M ; Yazdani S ; Cheung S. O ; Singh A ; Ghafoori N ; American Society of Civil Engineers (ASCE); Architectural Institute of Japan (AIJ); Chartered Institute of Building (CIOB); et al.; University of Nevada Las Vegas (UNLV), College of Engineering; Wayne State College of Engineering ; Sharif University of Technology
Research Publishing Services
2011
Abstract
Several investigators worked on various aspects of tensile behavior of concrete because of its wide usage in structural design. One of the observable phenomena during tensile failure of concrete is strain softening, i.e. a negative slope in the stress-deformation diagrams. There are many kinds of experiment-based softening curves for concrete. In current research, use of newly introduced concept of fractal geometry and a failure model yields to a new softening curve for concrete. This new curve is denominated "Quasi-fractal" softening curve, which is a theorybased softening model. Comparison of Quasi-fractal softening curve with a set of proposed experimental softening curves has been...
A plasticity-based constitutive model for the behavior of soil-structure interfaces under cyclic loading
, Article Transportation Geotechnics ; Volume 14 , 2018 , Pages 41-51 ; 22143912 (ISSN) ; Toufigh, V ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
In this study, a new plasticity-based constitutive model is proposed for the behavior of soil-structure interfaces under monotonic and cyclic loadings. The features of the interface including the strain-softening behavior, phase transformation, steady-state, and dilatancy behavior were described by the proposed model with satisfactory accuracy. The proposed model does not require additional concepts such as damage or disturbance, and the model parameters can be obtained easily using straight-forward analyses of the results obtained from constant normal stress tests. Moreover, the results of the proposed model showed its capability in predicting the experimental results obtained from various...
Finite Element Modelling of Damage in FRC using Microplane Method
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Mohammad Taghi (Supervisor)
Abstract
In concrete which is a quasi-brittle material failure initially occurs between aggregate and mortars. Fibers of all orientations, randomly embedded in FRC, serve to restrict and delay the coalescence of micro-cracks, micro-voids and micro-slips into wide continuous cracks. While the fibers increase the uniaxial tensile and compressive strength only moderately, they are very effective for enhancing the ductility and energy absorption capability. This elevates structure resistance to impact, ground-shock and blast. One of the most successful efforts toward reaching a macroscopic model which can take micromechanical properties into account is the Microplane model. In this microscopic...
A nonlocal computational homogenization of softening quasi-brittle materials
, Article International Journal for Numerical Methods in Engineering ; Volume 119, Issue 8 , 2019 , Pages 712-736 ; 00295981 (ISSN) ; Saadat, M. A ; Sharif University of Technology
John Wiley and Sons Ltd
2019
Abstract
In this paper, a computational counterpart of the experimental investigation is presented based on a nonlocal computational homogenization technique for extracting damage model parameters in quasi-brittle materials with softening behavior. The technique is illustrated by introducing the macroscopic nonlocal strain to eliminate the mesh sensitivity in the macroscale level as well as the size dependence of the representative volume element (RVE) in the first-order continuous homogenization. The macroscopic nonlocal strains are computed at each direction, and both the local and nonlocal strains are transferred to the microscale level. Two RVEs with similar geometries and material properties are...
Interpretation of tensile softening in concrete, using fractal geometry
, Article Scientia Iranica ; Volume 15, Issue 1 , 2008 , Pages 8-15 ; 10263098 (ISSN) ; Mofid, M ; Sharif University of Technology
Sharif University of Technology
2008
Abstract
Concrete is a heterogeneous material with a wide variety of usage in structural design. Concrete under tension exhibits strain softening, i.e., a negative slope in the stress-deformation diagrams. Different softening curves have been proposed in the literature to interpret this phenomenon. In current research, a new softening curve for concrete has been proposed by using the newly introduced concept of fractal geometry. This new softening curve is denominated a 'Quasi-fractal' softening curve and consists of two parts, a linear portion at the beginning and an exponential portion in the rest of the curve. A comparison of a "Quasi-fractal" softening curve with a set of proposed experimental...
H-adaptive mesh refinement for shear band localization in elasto-plasticity Cosserat continuum
, Article Communications in Nonlinear Science and Numerical Simulation ; Volume 10, Issue 3 , 2005 , Pages 253-286 ; 10075704 (ISSN) ; Tabarraie, A. R ; Gharehbaghi, S. A ; Sharif University of Technology
2005
Abstract
In this paper, an h-adaptive mesh refinement is presented based on the gradient of deformation in the modeling of localization due to material instability. As the classical continuum models suffer from pathological mesh dependence in the strain-softening models, the governing equations are regularized by adding rotational degrees-of-freedom to the conventional degrees-of-freedom. Adaptive strategy using element elongation is applied to compute the distribution of required element size using the estimated error distribution. Once the new element size and its alignment have been indicated, an automated procedure is used to construct the mesh according to a predetermined size and elongation...
Implementation of an Explicit Finite Element Program for Simulation of Concrete Behavior Via Microplane Model
, M.Sc. Thesis Sharif University of Technology ; Vafaei, Abolhassan (Supervisor) ; Shahbeyk, Sharif (Supervisor)
Abstract
In this research study, two constitutive models of improved Microplane are presented. The microplane model M1 is capable of simulation of a brittle aggregate material that undergoes progressive tensile fracturing or damage. It is assumed that the normal stress on a plane of any orientation within the material is a function of only the normal strain on the same microplane. This strain is further assumed to be equal to the resolved component of the macroscopic strain tensor, while the stress on the microplane is not equal to the resolved component of the macroscopic stress tensor. This model also is capable of simulating realistic tensile stress-strain curve with strain-softening and reduction...
Non-linear stress response of non-gap-spanning magnetic chains suspended in a newtonian fluid under oscillatory shear test: a direct numerical simulation
, Article Physics of Fluids ; Volume 29, Issue 10 , 2017 ; 10706631 (ISSN) ; Taghizadeh Manzari, M ; Fatehi, R ; Sharif University of Technology
Abstract
Adirect numerical simulation approach is used to investigate the effective non-linear viscoelastic stress response of non-gap-spanning magnetic chains suspended in a Newtonian fluid. The suspension is confined in a channel and the suspended clusters are formed under the influence of a constant external magnetic field. Large amplitude oscillatory shear (LAOS) tests are conducted to study the non-linear rheology of the system. The effect of inertia on the intensity of non-linearities is discussed for both magnetic and non-magnetic cases. By conducting magnetic sweep tests, the intensity and quality of the non-linear stress response are studied as a function of the strength of the external...
Hot deformation of PM Al6061 alloy produced by sintering and powder extrusion
, Article Powder Metallurgy ; Volume 51, Issue 4 , July , 2008 , Pages 354-360 ; 00325899 (ISSN) ; Simchi, A ; Sharif University of Technology
2008
Abstract
Compression test was used to study the deformation behaviour of sintered (12% porosity) and powder extruded (1% porosity) Al6061 alloy at high temperatures ranging from 350 to 500°C. The flow curves of the materials were determined at strain rates of 0.001, 0.01 and 0.1 s-1. The extruded alloy exhibited plastic instability in the form of bulging and formation of shear bands. The deformation activation energy of the extruded material was determined to be QI=77±16 kJ mol-1 (T<450°C) and OII=136±12 kJ mol-1 (T≥450°C). The values of activation energy and appearance of strain softening in the stress-strain curves revealed that thermally activated restoration processes, i.e. dynamic recovery and...
3D finite element modeling of shear band localization via the micro-polar Cosserat continuum theory
, Article Computational Materials Science ; Volume 49, Issue 4 , 2010 , Pages 720-733 ; 09270256 (ISSN) ; Yadegari, S ; Biabanaki, S. O. R ; Sharif University of Technology
Abstract
In this paper, a micro-polar continuum model is presented based on the Cosserat theory for 3D modeling of localization phenomena. Since the classical continuum model suffers from the pathological mesh-dependence in strain localization problem, the governing equations are regularized by adding the rotational degrees-of-freedom to conventional degrees-of-freedom. The fundamental relations in three-dimensional Cosserat continuum are presented and the internal length parameters are introduced in the elasto-plastic constitutive matrix to control the shear bandwidth. The mesh independency of Cosserat model in strain-softening problem is verified and the effect of internal parameters is...
The behavior of a limy cemented gravely sand under static loading-case study of Tehran alluvium
, Article Electronic Journal of Geotechnical Engineering ; Volume 13 H , 2008 ; 10893032 (ISSN) ; Seiphoori, A ; Rahmati, A ; Sharif University of Technology
2008
Abstract
The majority of the city of Tehran, Iran has been developed on cemented coarse-grained alluvium. In order to understand the mechanical behavior of this soil, a series of triaxial compression tests (CD, CU) were performed on uncemented and artificially cemented samples. Hydrated lime was used as the cementation agent for sample preparation to model the Tehran cemented deposit. The tests were performed on artificially cemented samples after an appropriate curing time. The effect of confining pressure, cement content and fine content is investigated in this research. The tests results show that peak shear strength is followed by strain softening for all cemented samples. Shear strength...