Loading...
Search for:
crystal-plasticity
0.006 seconds
Total 27 records
Simulation of orthogonal micro-cutting of FCC materials based on rate-dependent crystal plasticity finite element model
, Article Computational Materials Science ; Vol. 86, issue , April , 2014 , pp. 79-87 ; ISSN: 09270256 ; Movahhedy, M. R ; Akbari, J ; Sharif University of Technology
Abstract
Micro-machining of face centered cubic (FCC) metallic materials is simulated via the theory of rate-dependent crystal plasticity. This approach accounts for slip systems and crystallographic orientations in its constitutive framework in order to accurately model the evolution of localized shear band formed during severe plastic deformation of crystalline materials. Through developing a user-defined subroutine in the ABAQUS/Explicit FE platform, the constitutive model is implemented and used to study the influence of workpiece crystallographic orientation on the cutting and thrust specific energies of the process. Due to the high rate of deformation, mechanical properties of texture can be...
Numerical study on the effects of main BCC rolling texture components on the formability of sheet metals
, Article International Journal of Advanced Manufacturing Technology ; Volume 80, Issue 1-4 , March , 2015 , Pages 245-253 ; 02683768 (ISSN) ; Assempour, A ; Sharif University of Technology
Springer-Verlag London Ltd
2015
Abstract
Crystallographic texture considerably affects the formability of crystalline materials. In this paper, the effects of BCC ideal rolling fibers—including α, ε, η, γ, and ξ fibers—on the sheet formability are numerically studied. The simulations are based on the numerical procedure developed by the authors in [1] in which a rate dependent crystal plasticity model along with the power law hardening are employed in a user material subroutine to model the behavior of crystalline materials. In order to determine FLD—in a M-K type approach—second-order derivative of sheet thickness variations with respect to time is used as necking criterion. The calculated FLDs of the fibers are compared with each...
Prediction of ideal orientations and lattice rotations of FCC crystals in the equibiaxial tension loading: A rate-dependent crystal plasticity approach
, Article Mathematics and Mechanics of Solids ; Volume 21, Issue 10 , 2016 , Pages 1247-1259 ; 10812865 (ISSN) ; Khajeh Salehani, M ; Assempour, A ; Sharif University of Technology
SAGE Publications Inc
Abstract
This paper focuses on the determination of the complete set of ideal orientations of FCC materials in the equibiaxial tension mode of deformation. The simulations are based on the numerical procedure developed by the authors in which, a rate-sensitive crystal plasticity model with Secant hardening law was employed. The resulting nonlinear system of equations is solved by the modified Newton-Raphson method. An Euler space scanning method is used to obtain the ideal orientations of a deformation mode. In this method some initial orientations which are evenly spaced in the Euler space are selected and their evolutions into the ideal orientations are tracked. To verify the accuracy of the...
Coupled continuum damage mechanics and crystal plasticity model and its application in damage evolution in polycrystalline aggregates
, Article Engineering with Computers ; 2021 ; 01770667 (ISSN) ; Assempour, A ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
In the present study, damage initiation and growth in a polycrystalline aggregate are investigated. In this regard, an anisotropic continuum damage mechanics coupled with rate-dependent crystal plasticity theory is employed. Using a thermodynamically consistent procedure, a finite deformation formulation is derived. For this purpose, the damage tensor is incorporated in the crystal plasticity formulation for a cubic single crystal. The damage evolution is considered to be dependent on the history of damage, equivalent plastic strain, stress triaxiality, and Lode parameters. This material model is implemented in the commercial finite-element code Abaqus/Standard by developing a user material...
Crystal plasticity modeling and experimental characterization of strain localization and forming limits in ferrite-pearlite steels
, Article International Journal of Solids and Structures ; Volume 233 , December , 2021 ; 00207683 (ISSN) ; Kardan Halvaei, M ; Assempour, A ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The main objective of this study is to predict the deformation behavior, strain localization, and forming limits of ferrite-pearlite steels by incorporating the contributions of the microstructural characteristics and mechanical properties of the underlying microstructure. A realistic microstructure-based micromechanical approach in the framework of the crystal plasticity (CP) model was carried out using the periodic representative volume element (RVE) generated from the scanning electron microscopy (SEM) image. The homogenized stress–strain curve of the realistic RVE was validated with the experimental data with an error of less than 6.71% at large strains. Afterward, the initial...
Coupled continuum damage mechanics and crystal plasticity model and its application in damage evolution in polycrystalline aggregates
, Article Engineering with Computers ; Volume 38 , 2022 , Pages 2121-2135 ; 01770667 (ISSN) ; Assempour, A ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2022
Abstract
In the present study, damage initiation and growth in a polycrystalline aggregate are investigated. In this regard, an anisotropic continuum damage mechanics coupled with rate-dependent crystal plasticity theory is employed. Using a thermodynamically consistent procedure, a finite deformation formulation is derived. For this purpose, the damage tensor is incorporated in the crystal plasticity formulation for a cubic single crystal. The damage evolution is considered to be dependent on the history of damage, equivalent plastic strain, stress triaxiality, and Lode parameters. This material model is implemented in the commercial finite-element code Abaqus/Standard by developing a user material...
Prediction of Strain, Stress, and Microstructure in Sever Plastic Deformation of Equal Channel Angular Extrusion
, Ph.D. Dissertation Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
Sever plastic deformation can be used for decreasing the grain size and increasing the mechanical properties. In this method a square or circular cross section specimen is passed from two intersecting channel with equal cross section. Thereby, a large plastic strain without change of cross section is produced in the specimen. This large strain is the main reason for the interest of researchers in many fields. In the experimental research fields, researchers can study the response of material in the large plastic strain range, investigation of stage III of hardening and after it, change of microstructure to submicron and Nano, and increase of strength simultaneously with preserving of...
Modeling the Microstructure Evolution and Mechanical Properties of Al-Mg-Si alloys During Thermomechanical Treatment
, Ph.D. Dissertation Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
The Al-Mg-Si alloys are an important group of industrial materials used extensively in the automotive and aerospace industry, due to their high strength to weight ratio, good corrosion resistance and the recycle ability. In order to achieve a combination of optimized microstructure and properties during the production processes, the study of deformation behavior and heat treatment of these alloys is necessary. Therefore, the prediction of microstructural evolution and mechanical properties as a function of alloy chemical composition and thermomechanical treatment is important for these alloys, from both the scientific and industrial aspects. In the present research, the flow behavior of this...
Mechanical Properties of Two-Phase Microstructure in Nickel Based Superalloys with Molecular Dynamics Method
, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza (Supervisor)
Abstract
Nickel based superalloys are widely used in turbines since they are highly resistant to static, fatigue and creep loadings at high temperatures. Efficiency of turbines can be increase by application and development of these materials, which leads to reduced energy consumption. Nickel based superalloys constitutes of two phases, γ and γ' with multiscale behaviour. Thus to better understand the behaviour of this material, its behaviour should be studied across different scales.Molecular dynamics is used to model mechanical behaviour of this superalloy. This method is used for atomistic simulation of materials in which forces between atoms are modelled using an interatomic potential. Different...
Deformation mode dependency of stable orientations: From plane strain compression to equibiaxial tension
, Article Philosophical Magazine ; Volume 95, Issue 7 , Feb , 2015 , Pages 794-803 ; 14786435 (ISSN) ; Khajeh Salehani, M ; Assempour, A ; Mehdigholi, H ; Sharif University of Technology
Taylor and Francis Ltd
2015
Abstract
Prediction of stable orientations is a key subject in the crystal plasticity literature. This work deals with the effects of deformation mode on the resulted stable orientations and texture evolution of FCC materials. The simulations are based on the numerical procedure developed by the authors in previous works in which, a rate-sensitive crystal plasticity model with Secant hardening law was employed. The resulting non-linear system of equations is solved by the modified Newton-Raphson method. In order to obtain the stable orientations for a deformation mode, initial orientations evenly spaced in the Euler space are selected and their evolution into the stable orientations is tracked. The...
Ideal orientations of BCC crystals under equibiaxial tension loading
, Article Mathematics and Mechanics of Solids ; Volume 21, Issue 8 , 2016 , Pages 1026-1042 ; 10812865 (ISSN) ; Hajian, M ; Assempour, A ; Sharif University of Technology
SAGE Publications Inc
Abstract
Ideal orientations are one of the material characteristics of the applied mode of deformation. The transfer of material texture to orientations near specific ideal orientations can improve the mechanical properties of the material. In this paper, we focus on the determination of ideal orientations of BCC crystals under the equibiaxial tension mode of deformation. To do this, an Euler space scanning method based on a crystal plasticity approach is presented. In this method some initial orientations which are evenly spaced in the Euler space are selected and their evolutions into the ideal orientations are tracked. The loading is applied incrementally until all of the lattice spin components...
Crystal plasticity modeling of the effect of precipitate states on the work hardening and plastic anisotropy in an Al-Mg-Si alloy
, Article Computational Materials Science ; Vol. 83 , 2014 , pp. 78-85 ; ISSN: 09270256 ; Karimi Taheri, A ; Kim, H. S ; Sharif University of Technology
Abstract
In this study the influence of precipitates on the mechanical properties and plastic anisotropy of an age hardenable aluminum alloy during uniaxial loading was investigated using crystal plasticity modeling. The kinetics model of Myhr et al. was used to obtain the solute and precipitate features after different cycles of aging treatment. The amounts of solute, precipitate size and volume fraction, and dislocation density varying during deformation, were used to calculate the slip system strength. An explicit term was obtained based on the elastic inclusion model for the directional dependency of internal stress developed by non-shearable rod shape precipitates. Also, a dislocation evolution...
Experimental and crystal plasticity evaluation of grain size effect on formability of austenitic stainless steel sheets
, Article Journal of Manufacturing Processes ; Volume 47 , 2019 , Pages 310-323 ; 15266125 (ISSN) ; Assempour, A ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Effects of the grain size on the forming limits of stainless steel 316 L sheets are investigated using crystal plasticity finite element method (CPFEM) by modeling of all grains. For preparing simulation models with different grain morphology, a grain generator code is developed. Using data from metallographic images, texture, and material properties, the developed code can be used for preprocessing of CPFEM. In order to extract mechanical and metallurgical data required for CPFEM, some experiments are carried out on different samples. Moreover, for the purpose of implementing the crystal plasticity formulations, an Abaqus user material subroutine (UMAT) is developed. Concerning the...
Simulation of the Chip Formation and Dynamic Analysis of Micro-Milling Process Considering Size Effects
, Ph.D. Dissertation Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Akbari, Javad (Supervisor)
Abstract
Micromilling is one of the promising micromanufacturing processes used for creating 3D complex micro-scale features such as those used in MEMS devices. The mechanism of chip formation in this technique is different from that in conventional machining, because the size effects due to hardening behavior of microstructures at micro-scales and also the crystallographic orientation of a workpiece texture affects the mechanical behavior where a severe plastic deformation occurs in an induced shear band in front of the tool edge. In the present thesis, micromachining process is investigated by considering these effects. In order to capture the effects of size scale during high speed and large...
Investigation of Texture Effects on the Deformation of Sheet Metals using Crystal Plasticity Theory
, M.Sc. Thesis Sharif University of Technology ; Assempour, Ahmad (Supervisor) ; Mehdigholi, Hamid (Co-Advisor)
Abstract
The orientations which predominate in a final orientation distribution resulted from a specific deformation mode are the ideal orientations. There is a set of ideal orientations for each of crystal structures under a predefined mode of deformation. Ideal orientations are one of the material characteristics in the applied mode of deformation. The material texture strongly influences its final properties and affects the material behaviour in the subsequent forming processes.
In this project, final texture of 1010 steel sheet resulted from simple tension mode of deformation is investigated computationally and experimentally. The calculated texture based on the simulation procedure is...
In this project, final texture of 1010 steel sheet resulted from simple tension mode of deformation is investigated computationally and experimentally. The calculated texture based on the simulation procedure is...
Evaluation of Deformation and Formability Behaviors of the Ferritic-Pearlitic Steel Sheets by Employing the Experimental Approaches and Micromechanical Modeling
, Ph.D. Dissertation Sharif University of Technology ; Assempour, Ahmad (Supervisor)
Abstract
A broad range of plain carbon steels have ferrite-pearlite microstructures, which are used in many industrial applications due to the good strength and formability provided by the typical combination of ferrite grains and pearlite colonies. The mechanical behavior of ferrite-pearlite steels inherently originates from the configurations of ferrite grains and pearlite colonies, which comprised alternating lamellae of cementite with randomly distributed orientations in a ferrite matrix. In this thesis, three different experimental-numerical approaches were employed to investigate the deformation behavior, damage mechanisms, and formability of the ferrite-pearlite steels. At the first step, two...
Experimental and Numerical Evaluation of Grain Morphology Effect on Formability of Sheet Metals Using Coupled Crystal Plasticity and Damage Mechanics
, Ph.D. Dissertation Sharif University of Technology ; Assempour, Ahmad (Supervisor)
Abstract
In this dissertation, using experimental and numerical methods, the effects of grain morphology on the formability of sheet metals are investigated. In this regard, in the first stage, by conducting heat treatment on two different sheet metals with bcc and fcc crystal structures, different grain sizes are produced. Using metallographic observations, these grain structures are examined and the grain sizes are measured. Tensile test and Nakazima formability test have been implemented on these specimen. The grains are also shaped in the rolling process and different grain morphologies are created. In the second stage, a software has been developed to generate various grain structures and...
Multi-scale modeling of plastic deformations in nano-scale materials; transition to plastic limit
, Article International Journal for Numerical Methods in Engineering ; Volume 109, Issue 8 , 2017 , Pages 1180-1216 ; 00295981 (ISSN) ; Jahanshahi, M ; Sharif University of Technology
Abstract
A large amount of research in computational mechanics has biased toward atomistic simulations. This trend, on one hand, is due to the increased demand to perform computations in nanoscale and, on the other hand, is due to the rather simple applications of pairwise potentials in modeling the interactions between atoms of a given crystal. The Cauchy–Born (CB) hypothesis has been used effectively to model the behavior of crystals under different loading conditions, in which the comparison with molecular dynamics simulations presents desirable coincidence between the results. A number of research works have been devoted to the validity of CB hypothesis and its application in post-elastic limit....
Experimental and Numerical Study of Sheet Metals Formability based on Crystal Plasticity and Presentation of High Formability Fibers
, Ph.D. Dissertation Sharif University of Technology ; Assempour, Ahmad (Supervisor)
Abstract
In the classical theories of plasticity, plastic deformation of material is modeled with a macro- scopic viewpoint and without considering the existing physical mechanisms at the crystal scale. However, plastic deformation stems from slip phenomena and evolution of crystalline structure. Furthermore the effects of initial texture of material on its mechanical properties, like formability, and also texture evolution of material can only be calculated by considering these physical mecha- nisms.The main purpose of this thesis is to predict forming limit diagrams of sheet metals based on crystal plasticity approach by considering the effect of initial material texture and presentation of...
Modeling of the Mechanical Behavior of Shape Memory Alloys under Cyclic Loading Considering Detwinning-induced Plasticity and Transformation-induced Plasticity
, Ph.D. Dissertation Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeid (Supervisor) ; Arghavani Hadi, Jamal (Co-Supervisor) ; McGarry, Patrick (Co-Supervisor)
Abstract
The main goal of the current study is to incorporate the effect of microstructural deformation mechanisms, such as detwinning-induced plasticity, into constitutive and computational modeling of NiTi shape memory alloys. Therefore, based on thermodynamic considerations a new inelastic mechanism, detwinning-induced plasticity (DIP), is proposed for modelling the response of NiTi SMAs to cyclic loading. DIP is incorporated into a constitutive framework that also includes other well-established inelastic mechanisms of phase transformation, transformation-induced plasticity, residual martensite and detwinning. The model is constructed at the single crystal scale using the framework of...