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    A hypoelasto-plastic finite strain simulation of powder compaction processes with density-dependent endochronic model

    , Article International Journal of Solids and Structures ; Volume 41, Issue 22-23 , 2004 , Pages 6081-6110 ; 00207683 (ISSN) Khoei, A. R ; Bakhshiani, A ; Sharif University of Technology
    In this paper, a new approach is developed based on an endochronic density-dependent plasticity model for describing the isothermal deformation behavior of metal powder at low homologous temperature. As large deformations are observed in powder compaction processes, the endochronic constitutive model is presented based on large strain plasticity and an integration scheme is established for the rate constitutive equations. Endochronic constitutive equations are established based on coupling between deviatoric and hydrostatic behavior. The elastic response is stated in term of hypoelastic model and endochronic constitutive equations are stated in unrotated frame of reference. Finally, the... 

    A three-invariant cap model with isotropic-kinematic hardening rule and associated plasticity for granular materials

    , Article International Journal of Solids and Structures ; Volume 45, Issue 2 , 2008 , Pages 631-656 ; 00207683 (ISSN) DorMohammadi, H ; Khoei, A. R ; Sharif University of Technology
    In this paper, a three-invariant cap model is developed for the isotropic-kinematic hardening and associated plasticity of granular materials. The model is based on the concepts of elasticity and plasticity theories together with an associated flow rule and a work hardening law for plastic deformations of granulars. The hardening rule is defined by its decomposition into the isotropic and kinematic material functions. The constitutive elasto-plastic matrix and its components are derived by using the definition of yield surface, material functions and non-linear elastic behavior, as function of hardening parameters. The model assessment and procedure for determination of material parameters... 

    An investigation on the effect of carbon and silicon on flow behavior of steel

    , Article Materials and Design ; Volume 23, Issue 3 , 2002 , Pages 271-276 ; 02641275 (ISSN) Serajzadeh, S ; Karimi Taheri, A ; Sharif University of Technology
    Elsevier Ltd  2002
    The effect of carbon and silicon on the occurence of dynamic recrystallization as well as on the flow stress of steel was investigated. For this purpose, three grades of steels including low carbon, medium carbon and high silicon low carbon steel were examined. Single hit experiments at temperatures of 900-1200 °C and strain rate of 0.01-2 s-1 were performed to determine the phase transformation kinetics. Different socking times were utilized to detect the effect of initial austenite grain size on the kinetics of dynamic recrystallization and flow behavior of the steels. It was found that increasing the carbon content leads to a higher rate of dynamic recrystallization at high temperatures... 

    Damage-plasticity model for mixed hinges in steel frames

    , Article Journal of Constructional Steel Research ; Volume 67, Issue 8 , 2011 , Pages 1272-1281 ; 0143974X (ISSN) Kazemi, M. T ; Asl, M. H ; Sharif University of Technology
    A damage-plasticity based mixed axial-shear-flexural (PVM) link element for the inelastic analysis of frames is introduced in this paper. The multi-surfaces yield concept is utilized in the definition of the element. The yield surfaces are defined in deformation space and interaction of axial-shear-flexural deformations is considered by defining non-rectangular yield surfaces. The element is capable of considering damage and post-peak softening behavior. The analytical results of introduced element are verified by existing experimental results of steel beam to column connection and it is indicated that the analytical results have reasonable agreement with the test results. Nonlinear dynamic... 

    Development of biodegradable food packaging plastic films

    , Article Iranian Journal of Science and Technology, Transaction B: Technology ; Volume 27, Issue 2 , 2003 , Pages 299-304 ; 03601307 (ISSN) Frounchi, M ; Dadbin, S ; Karimi, S ; Sharif University of Technology
    Biodegradable thermoplastic films suitable for use in food packaging were produced. These films were mainly based on thermoplastic starch. The major task included research into thermal conversion of starch in a compression molding process and also under high shear conditions in an extruder in the presence of suitable plasticizers. The destruction of crystalline structure resulted in amorphous structure with thermoplastic properties. Films were rather transparent but slightly brown in color and had a specific smell. The films showed sufficient plasticity and acceptable tensile strength and elongation. The effect of plasticizer content on the final properties of the film was investigated. The... 

    Numerical modeling of MDOF structures with sliding supports using rigid-plastic link

    , Article Earthquake Engineering and Structural Dynamics ; Volume 30, Issue 1 , 2001 , Pages 27-42 ; 00988847 (ISSN) Vafai, A ; Hamidi, M ; Ahmadi, G ; Sharif University of Technology
    In this paper, the responses of multi-degree-of-freedom (MDOF) structures on sliding supports subjected to harmonic or random base motions are investigated. Modeling of the friction force under the foundation raft is accomplished by using a fictitious rigid link which has a rigid-perfectly plastic material. This will result in identical equations of motion for the sliding structure, both in the sliding and non-sliding (stick) phases which greatly simplifies the implementation of the method into a numerical algorithm. In this model the phase transition times are determined with high accuracy. This has two advantages: first, it prevents the so-called high-frequency oscillation of the relative... 

    Brace-frame interaction in tension braced MRFs

    , Article International Conference on Numerical Analysis and Applied Mathematics, ICNAAM 2008, Psalidi, Kos, 16 September 2008 through 20 September 2008 ; Volume 1048 , 2008 , Pages 364-367 ; 0094243X (ISSN); 9780735405769 (ISBN) Lotfollahi, M ; Mofid, M ; Alinia, M. M ; Greek Ministry of Education and Religious Affairs; European Soc. Computational Methods in Sci. Eng. (ESCMSE) ; Sharif University of Technology
    This study investigates the possibility of sequential failure analysis of Tension Braced Moment Resisting Frames (TBMRFs) by examining its performance in the linear and nonlinear stages under idealized seismic loading conditions. The results obtained from rigorous analyses by means of numerical methods are utilized to set up and calibrate an analytical model which would appropriately differentiate the contribution shares of the frame and the bracing elements. The paper provides information on key response parameters, including interaction value between frame and brace elements, as well as tensile strength capacity and ductility capability of such systems. © 2008 American Institute of Physics... 

    Effect of rolling strain on transformation induced plasticity of austenite to martensite in a high-alloy austenitic steel

    , Article Journal of Materials Processing Technology ; Volume 203, Issue 1-3 , 2008 , Pages 349-354 ; 09240136 (ISSN) Bigdeli Karimi, M ; Arabi, H ; Khosravani, A ; Samei, J ; Sharif University of Technology
    Current studies show a growing interest on transformation induced plasticity (TRIP) in austenitic steels. Most researches are based on inducing plasticity via tensile stresses, so it seems interesting to accomplish these researches by compressive stresses. Rolling process is a suitable choice to make compressive stresses. In present work, the effects of a wide range of rolling strains (5%-60%) at 0 and 24 °C on the austenite to martensite transformation were investigated on high-alloy austenitic steel. For this purpose, XRD, hardness test and magnetic measurements were used. Results show that by increasing the amount of rolling strain, transformation of austenite to martensite generally... 

    An equivalent von Mises stress and corresponding equivalent plastic strain for elastic–plastic ordinary peridynamics

    , Article Meccanica ; Volume 54, Issue 7 , 2019 , Pages 1001-1014 ; 00256455 (ISSN) Asgari, M ; Kouchakzadeh, M. A ; Sharif University of Technology
    Springer Netherlands  2019
    Simple formulas for calculating equivalent von Mises stress and von Mises effective plastic strain in an elastic–plastic ordinary peridynamic analysis are proposed. The equivalent von Mises stress is calculated by equating the deviatoric part of strain energy obtained from classical continuum mechanics and peridynamics. The effective plastic strain is proposed so that it reduced to uniaxial plastic strain in uniaxial tension test. Two example problems of the plate with a hole and a central crack under tension are considered to verify the validity of the proposed formulas. The plots of von Mises stress, equivalent plastic strain, plastic zone area and horizontal and vertical displacements are... 

    Numerical properties of second order integration algorithms for plasticity models

    , Article Research and Applications in Structural Engineering, Mechanics and Computation - Proceedings of the 5th International Conference on Structural Engineering, Mechanics and Computation, SEMC 2013 ; 2013 , Pages 443-448 ; 9781138000612 (ISBN) Jahanshahi, M ; Sharif University of Technology
    Investigating the behavior of materials in plastic limit is very important in different fields of engineering. Due to the simplicity of implementation and numerical stability, implicit types of algorithms are conventionally used to deal with plasticity problems. The backward Euler method as a first order accurate algorithm has proven very efficient for integrating the rate form of differential equations governing the behavior of different plasticity models. However, it is desirable to have algorithms with superior performance and quadratic rate of convergence compared with backward Euler method. Many second order integration algorithms have been proposed in the literature which are majorly... 

    Elastic-plastic modeling of hardening materials using a corotational rate based on the plastic spin tensor

    , Article 2007 ASME Pressure Vessels and Piping Conference, PVP 2007, San Antonio, TX, 22 July 2007 through 26 July 2007 ; Volume 3 , 2008 , Pages 439-446 ; 0277027X (ISSN); 0791842819 (ISBN); 9780791842812 (ISBN) Ghavam, K ; Naghdabadi, R ; Sharif University of Technology
    In this paper based on the multiplicative decomposition of the deformation gradient, the plastic spin tensor and the plastic spin corotational rate are introduced. Using this rate (and also lograte), an elastic-plastic constitutive model for hardening materials are proposed. In this model, the Armstrong-Frederick kinematic hardening and the isotropic hardening equations are used. The proposed model is solved for the simple shear problem with the material properties of the stainless steel SUS 304. The results are compared with those obtained experimentally by Ishikawa [1]. This comparison shows a good agreement between the results of proposed theoretical model and the experimental data. As... 

    Arbitrary Lagrangian-Eulerian method in plasticity of pressure-sensitive material: Application to powder forming processes

    , Article Computational Mechanics ; Volume 42, Issue 1 , 2008 , Pages 13-38 ; 01787675 (ISSN) Khoei, A. R ; Anahid, M ; Shahim, K ; DorMohammadi, H ; Sharif University of Technology
    Springer Verlag  2008
    In this paper, an application of Arbitrary Lagrangian-Eulerian (ALE) method is presented in plasticity behavior of pressure-sensitive material, with special reference to large deformation analysis of powder compaction process. In ALE technique, the reference configuration is used for describing the motion, instead of material configuration in Lagrangian, and spatial configuration in Eulerian formulation. The convective term is used to reflect the relative motion between the mesh and the material. Each time-step is divided into the Lagrangian phase and Eulerian phase. The convection term is neglected in the material phase, which is identical to a time-step in a standard Lagrangian analysis.... 

    A three-invariant cap plasticity model with kinematic and anisotropic hardening rule for powder and granular materials

    , Article 9th International Conference on Computational Plasticity: Fundamentals and Applications, COMPLAS IX, Barcelona, 5 September 2007 through 7 September 2007 ; Issue PART 2 , 2007 , Pages 604-607 ; 9788496736290 (ISBN) Khoei, A. R ; DorMohammadi, H ; Sharif University of Technology
    In this paper, a three-invariant plasticity model is developed based on a single cap yield surface for the kinematic and anisotropic hardening behavior of powder and granular materials. The applicability of proposed plasticity model is demonstrated in numerical simulation of several triaxial and confining pressure tests on different powder and granular materials. © CIMNE, 2007  

    Axial effects investigation in fixed-end circular bars under torsion with a finite deformation model based on logarithmic strain

    , Article International Journal of Mechanical Sciences ; Volume 48, Issue 1 , 2006 , Pages 75-84 ; 00207403 (ISSN) Yeganeh, M ; Naghdabadi, R ; Sharif University of Technology
    In this paper the torsion problem of a circular bar with fixed ends is solved using a finite deformation constitutive model based on the corotational rates of the logarithmic strain. The logarithmic, Green-Naghdi and Eulerian corotational rates of the logarithmic strain are used in the model. The solution is based on a von Mises type yield function that incorporates isotropic and kinematic hardenings. For the kinematic hardening, a modified Armstrong-Fredrick hardening model with the corotational rate of the logarithmic strain is used. Assuming incompressible behavior, the fixed-end torsion problem is simplified to the simple shear problem. Solving the problem, the stress components are... 

    Numerical simulation of 3D powder compaction processes using cone-cap plasticity theory

    , Article Materials and Design ; Volume 26, Issue 2 , 2005 , Pages 137-147 ; 02613069 (ISSN) Khoei, A. R ; Azizi, S ; Sharif University of Technology
    Elsevier Ltd  2005
    In this paper, the numerical simulation of powder compaction processes is presented using a three-dimensional cap plasticity model. A cone-cap density-dependent plasticity model is developed based on a combination of a convex yield surface consisting of a failure envelope and a hardening elliptical cap for nonlinear behavior of powder materials in the concept of the generalized plasticity formulation. A general algorithm for the cap plasticity from the viewpoint of efficient numerical modeling is presented. The cap plasticity is performed within the framework of large FE deformation, in order to predict the non-uniform relative density distribution during powder die pressing. Finally, the... 

    Constitutive law of finite deformation elastoplasticity with proportional loadings

    , Article Journal of Pressure Vessel Technology, Transactions of the ASME ; Volume 135, Issue 6 , September , 2013 ; 00949930 (ISSN) Darijani, H ; Naghdabadi, R ; Sharif University of Technology
    In this paper, decomposition of the total strain into elastic and plastic parts is investigated for extension of elastic-type constitutive models to finite deformation elastoplasticity. In order to model the elastic behavior, a Hookean-type constitutive equation based on the logarithmic strain is considered. Based on this constitutive equation and assuming the deformation theory of Hencky as well as the yield criteria of von Mises, the elastic-plastic behavior of materials at finite deformation is modeled in the case of the proportional loading. Moreover, this elastoplastic model is applied in order to determine the stress distribution in thick-walled cylindrical pressure vessels at finite... 

    The extended finite element method for large deformation ductile fracture problems with a non-local damage-plasticity model

    , Article Engineering Fracture Mechanics ; Volume 112-113 , 2013 , Pages 97-125 ; 00137944 (ISSN) Broumand, P ; Khoei, A. R ; Sharif University of Technology
    An enriched-FEM technique is presented for the crack growth simulation in large deformation ductile fracture problems using a non-local damage-plasticity model in the framework of eXtended Finite Element Method (X-FEM). The Lemaitre damage-plasticity model is used to capture the material degradation effect, in which the non-locality is enforced by solving a Helmholtz type equation in combination with the governing equation of the system based on an operator-split technique. A convergence study is performed to investigate the performance of X-FEM technique in plasticity problems. The accuracy and effectiveness of proposed X-FEM damage-plasticity model are verified through several numerical... 

    Second order integration algorithms for j2 plasticity with generalized isotropic/kinematic hardening

    , Article Asian Journal of Civil Engineering ; Volume 13, Issue 2 , April , 2012 , Pages 203-232 ; 15630854 (ISSN) Jahanshahi, M ; Sharif University of Technology
    AJCE  2012
    In this work four algorithms are presented for the integration of equations governing the behavior of von Mises material in plastic limit. Two of them are single-step and the others are double-step algorithms. Single-step algorithms are straight forward extension of backward Euler method or midpoint rule while double-step algorithms are a combination of two. In past similar algorithms were proposed for special cases of isotropic/kinematic hardening; however the algorithms presented in this work are applicable to general isotropic/kinematic hardening laws. Theoretical as well as numerical aspects are presented for all integration schemes and elaborated for double-step algorithms which are... 

    Modelling of powder forming processes in transient-dynamic analysis of large plastic deformations

    , Article Advanced Materials Research, 13 July 2011 through 16 July 2011 ; Volume 445 , July , 2012 , Pages 362-367 ; 10226680 (ISSN) ; 9783037853467 (ISBN) Khoei, A. R ; Biabanaki, S. O. R ; Parvaneh, S. M ; Turkish Airlines; TTNET; Gedik Holding; Istanbul Development Agency ; Sharif University of Technology
    In this paper, a transient-dynamic analysis is presented for large deformation of powder forming process. The technique is employed using the contact friction algorithm and plasticity behavior of powder. The contact algorithm is applied by imposing the contact constraints and modifying the contact properties of frictional slip through the node-to-surface contact algorithm. A double-surface cap plasticity model is used for highly nonlinear behavior of powder. In order to predict the non-uniform density and stress distributions during powder die-pressing, the numerical schemes are examined for accuracy and efficiency in modeling of a set of powder components  

    3D dynamic modeling of large plastic deformations in powder die-pressing

    , Article Proceedings of the 10th International Conference on Technology of Plasticity, ICTP 2011, 25 September 2011 through 30 September 2011, Aachen ; September , 2011 , Pages 1010-1015 ; 9783514007840 (ISBN) Khoei, A. R ; Biabanaki, S. O. R ; Parvaneh, S. M ; Sharif University of Technology
    In this paper, a computational algorithm is presented in three-dimensional dynamic modeling of powder compaction processes. The contact node-to-surface algorithm is employed to impose the contact constraints in large deformation frictional contact, and the contact frictional slip is modified by the Coulomb friction law to simulate the frictional behavior between the rigid punch and the work-piece. The 3D nonlinear contact friction algorithm is employed together with a double-surface cap plasticity model within the framework of large FE deformation in order to predict the non-uniform relative density distribution during the dynamic simulation of powder die-pressing. Finally, the performance...