Loading...
Search for:
fld
0.005 seconds
Total 26 records
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...
Experimental and analytical studies on the prediction of forming limit diagrams
, Article Computational Materials Science ; Volume 44, Issue 4 , 2009 , Pages 1252-1257 ; 09270256 (ISSN) ; Eivani, A. R ; Akbarzadeh, A ; Sharif University of Technology
2009
Abstract
Metal forming processes are widely used in industrial productions, automobile bodies, food industries, oil refineries, and liquid and gas transmission systems. Analyzing these processes is very important to reduce wastes and optimize the processes. Study of some main factors such as physical and mechanical properties of material and its formability, die geometry, die material, lubrication and pressing speed has been the topic of many research projects. In this paper, forming limit diagrams (FLDs) for LC and ULC steels and the effect of different parameters like the work-hardening exponent, n, and the plastic strain ratio, r, on these diagrams have been evaluated and simulated using...
An experimental and theoretical study on the prediction of forming limit diagrams using new BBC yield criteria and M-K analysis
, Article Computational Materials Science ; Volume 44, Issue 4 , 2009 , Pages 1272-1280 ; 09270256 (ISSN) ; Eivani, A. R ; Akbarzadeh, A ; Sharif University of Technology
2009
Abstract
In the present paper, a comprehensive study on the prediction of forming limit diagrams (FLDs) for an AA3003-O aluminium alloy is developed theoretically and experimentally. For obtaining the experimental FLDs, an out-of-plane formability test was performed based on the technique proposed by Ozturk and Lee [F. Ozturk, D. Lee, J. Mater. Process. Technol. 170 (2005) 247-253]. The classical Marciniak-Kuczynski (M-K) model and some new yield criteria are utilized to simulate the necking phenomenon and calculate the limit strains theoretically. The employed yield functions are: the BBC2000, BBC2002, and BBC2003 yield criteria proposed by Banabic et al. [D. Banabic, S.D. Comsa, T. Balan, in:...
Analysis of P300 classifiers in brain computer interface speller
, Article 28th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS'06, New York, NY, 30 August 2006 through 3 September 2006 ; 2006 , Pages 6205-6208 ; 05891019 (ISSN); 1424400325 (ISBN); 9781424400324 (ISBN) ; Fazel Rezai, R ; Shamsollahi, M. B ; Sharif University of Technology
2006
Abstract
In this paper, the performance of five classifiers in P300 speller paradigm are compared. Theses classifiers are Linear Support Vector Machine (LSVM), Gaussian Support Vector Machine (RSVM), Neural Network (NN), Fisher Linear Discriminant (FLD), and Kernel Fisher Discriminant (KFD). In classification of P300 waves, there has been a trend to use SVM classifiers. Although they have shown a good performance, in this paper, it is shown that the FLD classifiers outperform the SVM classifiers. FLD classifier uses only ten channels of the recorded electroencephalogram (EEG) signals. This makes them a very good candidate for real-time applications. In addition, FLD approach does not need any...
A New Method Based on Crystal Plasticity Finite Element to Predict the Formability of Steel Sheets with Spheroidal Cementites
, Ph.D. Dissertation Sharif University of Technology ; Assempour, Ahmad (Supervisor)
Abstract
In this research, using the crystal plasticity finite element method, the effects of various microstructural features on behavior of spherical steel sheets have been investigated. The cementite phase ratio, the grain sizes of ferrite and cementite, and the percentage of residual pearlite in the steel structure due to incomplete annealing are the major microstructural parameters studied in this work. A grain generator software has been developed to generate ferrite grains as well as cementite particles distributed in the ferrite matrix. A hard coating with special properties as an intermediate layer around the cementite grains has been considered to simulate the contact between ferrite grains...
Extraction of the Forming Limit Diagram in Magnesium Microtubes Used in Stents by Modeling the Hydroforming Process in Abaqus Finite Element Software
, M.Sc. Thesis Sharif University of Technology ; Assempour, Ahmad (Supervisor)
Abstract
One of the common methods of removing blood clots is angioplasty with stents. Due to the fact that the mechanical properties of the stent are directly related to the microtube it is made of. Therefore, investigating the mechanical properties of microtubes is very important. One of the ways used to evaluate the plasticity of microtubes; Drawing a graph is the limit of shaping. The purpose of this research is to extract the forming limit diagram of magnesium microtube by simulating the hydroforming process in Abaqus software. First, in order to confirm the modeling, the hydroforming process for aluminum has been simulated and compared with the existing experimental results. The comparison...
The Effects of Retrogression and Aging Heat Treatment on the Mechanical Properties and Flow Limit Diagrams of Precipitation-harden-Able Aluminum Alloy
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor) ; Kazeminejad, Mohsen (Supervisor)
Abstract
Demand for high performance components has caused a propensity towards high strength alloys, especially 7000 series, having extended applications in aerospace, automotive and medical industries. Due to high strength, heat treatability, and optimum weight, these alloys have been implemented in various conditions, specifically AA7075, being directly used in airframes. Through the years, numerous attempts have been made to improve the corrosion and formability properties of these alloys, resulting in the development of various tempering methods such as retrogression and re-ageing. Despite achiving optimal properties, it has been of less interest through literature to assess the formability of...
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 Determination of Forming Limit Diagram of Two-layer Sheets Considering the Interface between Layers
, M.Sc. Thesis Sharif University of Technology ; Asempour, Ahmad (Supervisor)
Abstract
In recent years, two-layer sheets have been used in various industries. In this research, the formability of a two-layer sheet which is made of 1.35 mm steel and 0.45 mm copper sheets has been studied. The two-layer sheet used in this study was made by explosive welding method. In order to investigate the formability of the sheet, forming limit diagram was determined. First, Marciniak-Kuczynski (M-K) model was used. In order to determine forming limit diagram using this method, the two-layer sheet was equated with a single-layer sheet and MATLAB software was used. The two-layer sheet was also modeled in finite element software ABAQUS. In order to determine the forming limit diagram, Nakazima...
Investigate the Formation of Metal Sheets by Damage Mechanics
, M.Sc. Thesis Sharif University of Technology ; Asempoor, Ahmad (Supervisor)
Abstract
One of the oldest and most used methods in shaping metals is the formation of metal sheets. In designing the process of printing, it's important to know how much the strain on the sheet prior to slipping is. In order to predict the permissible strains in the two-axis stretch of the sheet, they introduced an empirical diagram called the shape-forming diagram. There are various methods for analyzing the formation of metallic sheets, which can be referred to by M-K method, GTN method, continuous damage mechanics method (CDM). In this research, we have tried to obtain the shape of a metal sheet in various strain paths by studying the method of CDM and modeling the mechanical behavior of the...
An Investigation on the Microstructure and Mechanical Properties of Almg6 Alloy-Carbon Nanotube Composite Produced by Accumulated Roll Bonding Process
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
In recent years, the use of high specific strength aluminum alloys in automotive and aerospace industries is in progress due to their energy savings. On the other hand, the carbon nanotubes (CNTs), due to their ultra-high strength and modulus of elasticity, have been considered as an excellent reinforcement for the metal matrix composites used in these industries. For production of these materials, the severe plastic deformation (SPD) has been known as a method of grain refinement to increase the strength and ductility. In this research, the composites of AlMg6 reinforced with CNT were produced by accumulated roll bonding (ARB) known as a SPD technique and their properties were compared...
Investigation on Formability of Two-layered Stainless Steel-copper Sheets with FLDs
, M.Sc. Thesis Sharif University of Technology ;
Abstract
In this research, two-layered sheets of copper and stainless steel 316 were produced by roll bonding. These sheets provide a combination of properties of copper and stainless steel; including high strength, thermal conductivity and corrosion resistance, as well as low weight and cost-efficient means of production. The effects of thickness reduction, different preheat temperatures and varying heating conditions after rolling on bond strength were studied. In some specimens, an aluminum sheet was used as a middle-layer, which significantly improved the bonding quality. In order to observe the interface of the bonded specimens, optical microscope images of the cross sections were studied....
On the Effects of Strain Rate and Heat on Forming Limit Diagrams
, M.Sc. Thesis Sharif University of Technology ; Asempour, Ahmad (Supervisor)
Abstract
Sheet metal forming is widely being used in the production fields. Improve of quality, production rate and efficiency of this process are important. Temperature and strain rate are the most effective parameters on the formability of sheet metals. Utilizing forming limit diagram is the most common method of determining the formability. In this study, forming limit diagram of AA3003 aluminum alloy is extracted in different temperatures and velocities using simulation of Nakazima test with Abaqus finite element software. The simulation results, indicate that at 250°C formability is about 3 times more than that at room temperature. increasing the velocity of the punch in low strain rates causes...
Implementation of Shear Stress in M-K Model for Determination of the Limit Strains
, M.Sc. Thesis Sharif University of Technology ; Asempour, Ahmad (Supervisor) ; Hashemi, Ramin (Co-Advisor)
Abstract
One of the most useful methods in metal forming is Sheet Metal Forming. Use of Forming limit diagrams (FLD) in designing is a conventional method. Therefore many experimental and theoretical efforts have been carried out in order to investigate the FLDs. Many ways to obtain this FLDs and their effective parameters have been studied. But the stress state at these studies is planar which lead to an untrue model for several metal forming process such as incremental sheet forming. With this technique, the forming limit curve (FLC) appears in a different pattern, revealing an enhanced formability, compared to conventional forming techniques. Therefore, in this study, the effect of through...
Formability analysis of Tailor Welded Blank Pridaction with Friction Stret Weld
, M.Sc. Thesis Sharif University of Technology ; Asempour, Ahmad (Supervisor) ; Naghdabadi, Reza (Supervisor)
Abstract
The Tilor welded blank (TWB) two or more sheets with different thickness or strength which are welded together. The automobile designer are searching for new methods to reduce the cars’ weight and producing cost in order to diminish fuel consumption so they can survive in the competitive market. One way to achieve to this seemingly Contradictory demands, is using TWB in cars’ body. One of the most applicable methods to investigate the formability of metals sheets, is Forming Limit Diagrams (FLD). Three ways to determine the FLD are: Analytical Method, Experimental Methods, and Numerical Method. The experimental method to determine FLD, require metal sheets to undergo in different strain...
The comparison of M-K and GTN models in prediction of forming limit diagrams
,
M.Sc. Thesis
Sharif University of Technology
;
Assempour, Ahmad
(Supervisor)
Abstract
Knowing the magnitude of the maximum strain before necking is of utmost importance in the processes of designing sheet metals. Thus, numerous experimental and theoretical efforts have been done to answer these questions. In order to predict allowed strains in biaxial stretching, an experimental diagram was introduced called “Forming Limit Diagram” in which major strain is plotted versus minor strain and if the corresponding point to the strain on the sheet is higher than this diagram, necking will occur. One of the most popular methods of obtaining forming limit diagrams is using a hemispherical rod for shaping sheet, which is named as “Nakazima Test” and then the critical strains are...
Experimental Study of High Strain Rate Effects on Steel Sheet Forming
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor)
Abstract
Strain rate dependence of plastic yield and failure properties displayed by most metals affects energies, forces and forming limits involved in high speed forming processes. This paper investigates the influence of the strain rate on the forming properties of some industrial sheet metals used in Automotive and Aerospace industries. First, Split Hopkinson Tensile Bar (SHTB) experiments are carried out to determine the influence of the strain rate on the materials’ stress-strain curves. Then, the SHTB results are used to model the constitutive behaviour of the metal sheets using the phenomenological Johnson-Cook (JC) and Voce models. Finally, forming limit diagrams (FLDs) are calculated using...
Effects of Bending on Forming Limit Diagram (FLD)Based on Marciniak & Kuczynski Method
, M.Sc. Thesis Sharif University of Technology ; Asempour, Ahmad (Supervisor)
Abstract
In designing sheet forming processes, finding out the value of the maximum strain before necking in sheets is extremely important. Therefore, many experimental and theoretical efforts have been carried out in order to answer this question. One of the most well-known and useful theoretical methods in this regard is the Marciniak - Kuczynski method which was introduced in 1967 and is still the topic of many researches. In this model, it is assumed that a groove as a defect primarily exists in the sheet and due to the weakness of this region, necking will initiate. Furthermore, the effects of various parameters such as sensitivity to strain rate, strain path, thickness, three dimensional...
Study on the Behavior of Ship’s Bottom Structure under Grounding Phenomenon
, M.Sc. Thesis Sharif University of Technology ; Abbaspour, Majid (Supervisor) ; Omidvar, Mohammad Taghi (Co-Advisor)
Abstract
Whenever and wherever there is shipping, there exist risks of marine accidents. Subsequently, such accidents at sea may result in potential economic loss,environmental pollution and fatalities. In fact, ship grounding accident is a type of marine accident that involves the impact of a ship on seabed or waterway side. It may result in the damage of the submerged part of the ship’s hull and in particularly the bottom structure; potentially leading to water ingress, which may at the end compromise the ship's structural integrity, stability, and finally safety. An overall view on groundings categorizes the accidents in two major groups: Soft Grounding and Hard Grounding. A soft grounding does...
Determination of Forming Limit Diagrams by Strain Gradient Theory
, M.Sc. Thesis Sharif University of Technology ; Asempour, Ahmad (Supervisor)
Abstract
In recent decades, the importance of theoretical and experimental researches on sheet metal forming has been revealed due to its wide-spreading applications. The purpose of these researches is to optimize the forming processes and minimize the existing imperfections. Since classical theories don’t include parameters for describing the dependence of metals behavior on size effects or inhomogeneous plastic deformation effects, gradient theories are considered in many researches. In gradient theories, this dependence is considered by changing the constitutive equations and the existence of higher order of strain gradient in zones with inhomogeneous deformation. By considering the localized and...