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finite-element-analysis
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Effects of design parameters and A f temperature on superelastic behaviour of Nitinol stent for application in biliary duct: finite element analysis [electronic resource]
, Article Materials Technology: Advanced Performance Materials ; Vol. 29, No. 2, 2014, 65-75 ; Sadrnezhaad, K ; Sharif University of Technology
Abstract
For more than a decade, stent implantation has been strategically used for solving gastrointestinal dilemmas such as biliary stenosis. Predicaments like insufficient radial strength, low twisting ability, inappropriate dynamic behaviour and restenosis are expected to be solved by the introduction of new designs. Superelastic Nitinol stent is an interesting alternative for minimising these tight spots. The application of finite element method to predict metallurgical and geometric behaviour of superelastic Nitinol stents for biliary duct dilatation is supported by conventional crimp tests. Model calculations show that all stents encounter the highest stress in their intersegment curvature....
Effect of material properties on the mechanical performance of nitinol esophageal stent: finite element analysis [electronic resource]
, Article Materials Science Forum ; Volumes 773 - 774, 2014, 9-17 ; Sadrnezhaad, K ; Kokabi, H. A ; Razani, M ; Mohagheghi, A. H ; Sharif University of Technology
Abstract
Stent placement has been a main approach to treat gastrointestinal diseases during past decade. Nitinol superelastic stents have been considered as a solution to such difficulties as restenosis after implantation, low twisting ability, inadequate radial mechanical strength and inappropriate dynamic behaviors associated with the ducts. In this paper, effects of Af temperatures on mechanical performance of z-shaped Nitinol wire stent under crimping test for clinical applications are investigated by finite element simulation. Having 60% crimping and high radial resistive strength, favorable superelastic behaviors are attained at Af temperature of 22°C. The performance of the stent is seen to be...
Finite element analysis of mechanical performance of nitinol biliary stent: effect of material properties [electronic resource]
, Article Materials Research Innovations ; Vol 17, No. 2, 2013, 53-59 ; Sadrnezhaad, K ; Sharif University of Technology
Abstract
Stent implantation has been regarded as a major strategy to solve gastrointestinal diseases such as biliary obstruction during the last decade. The application of nitinol superelastic stents has been recently considered for minimising such problems as restenosis after stent implantation, the ability to low stent twist, unsuitable dynamic behaviour and inadequate strength radial of stent. In the present article, the effects of material properties on mechanical performance of Z shaped nitinol wire stent under crushing test for clinical applications are studied by finite element modelling. Nitinol stent shows better mechanical and clinical performance after applying 90% crushing, less chronic...
Effects of Crimping on Mechanical Performance of Nitinol Stent Designed for Femoral Artery: Finite Element Analysis [electronic resource]
, Article Journal of Materials Engineering and Performance ; November 2013, Volume 22, Issue 11, pp 3228-3236 ; Sadrnezhaad, K ; Sharif University of Technology
Abstract
Nitinol stents are used to minimize improper dynamic behavior, low twistability, and inadequate radial mechanical strength of femoral artery stents. In this study, finite element method is used to investigate the effect of crimping and Austenite finish temperature (A f) of Nitinol on mechanical performance of Z-shaped open-cell femoral stent under crimping conditions. Results show that low A f Nitinol has better mechanical and clinical performance due to small chronic outward force, large radial resistive force, and appropriate superelastic behavior
Hot extrusion process modeling using a coupled upper bound-finite element method
, Article Journal of Manufacturing Processes ; Vol. 16, issue. 2 , 2014 , pp. 233-240 ; ISSN: 15266125 ; Serajzadeh, S ; Sharif University of Technology
Abstract
A thermo-mechanical model has been developed for modeling of hot extrusion processes. Accordingly, an admissible velocity field was first proposed by means of stream function method and then, extrusion pressure as well as temperature variations within the metal and the die were predicted employing a combined upper bound and Petrov-Galerkin finite element analysis. In order to evaluate the model predictions, hot extrusion of AA6061-10%SiCp was considered under both isothermal and non-isothermal conditions and the predicted force-displacement diagrams under various extrusion conditions were compared with the experimental ones and reasonable consistency was found between the two sets of results...
3D finite element analysis and experimental validation of constrained groove pressing-cross route as an SPD process for sheet form metals
, Article International Journal of Advanced Manufacturing Technology ; Volume 73, Issue 9-12 , August , 2014 , Pages 1291-1305 ; ISSN: 02683768 ; Abbaszadeh, M ; Mohebpour, S. R ; Eskandari, H ; Sharif University of Technology
Abstract
A new modification of constrained groove pressing (CGP) process named as constrained groove pressing-cross route (CGP-CR) was suggested for severe plastic deformation (SPD) of sheet form metals with great potential for fabricating high strength nanostructured sheets. This process is based on the conventional CGP process including some modifications. One pass of this process includes eight stages (four corrugation and four flattening) and involves 90° cross-rotation between each two stages. As a result of each CGP-CR pass, a strain magnitude of ∼2.32 is imparted to the sample. To simulate the process, finite element modeling (FEM) was carried out using three-dimensional finite element...
An investigation of the effects of socket joint flexibility in space structures
, Article Journal of Constructional Steel Research ; Volume 102 , November , 2014 , Pages 72-81 ; ISSN: 0143974X ; Maalek S ; Sharif University of Technology
Abstract
Connection of truss elements using socket joints is one of the more common practices in the construction of space structures. Although these hollow spherical joints may deform due to the applied loads, these deformations and the resulting effects on the member axial forces are usually ignored in the analysis and design. This work is an investigation of the effects of socket joint deformability on the behavior of space grid structures. Here, the load-deformation relationships obtained from a series of biaxial loading tests on actual socket joints have been used to represent their behavior in several finite-element analysis models. These models have been analyzed using a special-purpose...
A circularly polarized antenna based on the unidirectional resonant modes of a ferrite disk
, Article IEEE Transactions on Magnetics ; Volume 50, Issue 3 , 26 September 2013 , Pages 88-95 ; Rejaei, B ; Komjani, N ; Sharif University of Technology
Abstract
We propose a circularly polarized antenna with a wide axial ratio (AR) beamwidth that consists of a normally magnetized ferrite disk mounted on a ground plane. The device uses the resonant modes of the disk, which rotate only in the clockwise or counter-clockwise sense in the frequency range where the effective permeability of ferrite is negative. A semianalytical model is derived for the antenna fed by a single, conventional current probe and is validated numerically by finite element method. For a yttrium iron garnet disk with the radius and height of 5 and 1 mm, respectively, the results show a 3 dB AR beamwidth of 90° with an operation frequency, which can be tuned in the 4-4.5 GHz range...
Elevation and orientation of external loads influence trunk neuromuscular response and spinal forces despite identical moments at the L5-S1 level
, Article Journal of Biomechanics ; Vol. 47, issue. 12 , September , 2014 , p. 3035-3042 ; Shirazi-Adl, A ; Plamondon, A ; Arjmand, N ; Sharif University of Technology
Abstract
A wide range of loading conditions involving external forces with varying magnitudes, orientations and locations are encountered in daily activities. Here we computed the effect on trunk biomechanics of changes in force location (two levels) and orientation (5 values) in 4 subjects in upright standing while maintaining identical external moment of 15. Nm, 30. N. m or 45. Nm at the L5-S1. Driven by measured kinematics and gravity/external loads, the finite element models yielded substantially different trunk neuromuscular response with moderate alterations (up to 24% under 45 Nm moment) in spinal loads as the load orientation varied. Under identical moments, compression and shear forces at...
Comparison of the effects of different implant apical designs on the magnitude and distribution of stress and strain in bone: A finite element analysis study
, Article Journal of Long-Term Effects of Medical Implants ; Vol. 24, issue. 2-3 , 2014 , p. 109-120 ; Lafzi, A ; Raoofi, S ; Khademi, M ; Amid, R ; Movahhedy, M. R ; Torabi, H ; Sharif University of Technology
Abstract
Objectives: The aim of this study was to investigate the effects of implant design on the apex area and on stress and stress patterns within surrounding bone. Methods: Three commercially available implants with the same diameter (3.5 mm), same length (10-11 mm), and same complement abutment were selected for modeling as follows: (1) flat apical design with light tapering degree, (2) dome-shaped apical design with light tapering, and (3) flat apical design with intense tapering in one-third of the apical area. According to human cone-beam computed tomography (CBCT), the bone was modeled using a cortical thickness of 2 mm and cancellous bone. Forces of 100 N and 300 N in the vertical and 15°...
On the influence of shape and material used for the femoral component pegs in knee prostheses for reducing the problem of aseptic loosening
, Article Materials and Design ; Vol. 55, issue , March , 2014 , p. 416-428 ; Sahari, B. B ; Edwards, K. L ; Farahmand, F ; Jahan, A ; Hong, T. S ; Arumugam, M ; Sharif University of Technology
Abstract
The integration of materials selection and design are essential to the success of new product development, especially when applied to biomedical devices. The knee prosthesis, like any other implant, is a product that still lacks satisfactory design solutions for solving the problem of aseptic loosening. Stress shielding is one of the main causes of aseptic loosening that is intimately related to the overall design of the knee prosthesis. The design of the location pegs in the femoral component of the knee prosthesis is seen to have a critical effect on the stress shielding. In this study, therefore, different combinations of location peg geometries and material designs were assessed using...
Numerical analysis (finite element method) of brace effects on the adolescent idiopathic scoliosis during 24 hours
, Article Biomedical Engineering - Applications, Basis and Communications ; Vol. 26, issue. 3 , June , 2014 ; 10162372 ; Haghpanahi, M ; Parnianpour, M ; Ganjavian, M. S ; Kamyab, M ; Sharif University of Technology
Abstract
In the adolescent idiopathic scoliosis (AIS) treatment, a brace is prescribed to the patients who have 20 to 45° curves on their spines to prevent the disorder's advancement. For the analysis of Milwaukee brace effects during time, finite element models (FEMs) of the spine (the thoracolumbar region) and the ribcage (contained 10 pairs of the ribs and the sternum) were prepared for two patients. For modeling the spine part, a new element was used in which a disc (as viscoelastic 3D beam) and a vertebra (as rigid link) were modeled as an element and the ribs and the sternum modeled by 3D elastic beams. The gravity, Milwaukee brace constraints and the forces of the brace's different regions...
Using three-dimensional finite element analysis for simulation of residual stresses in railway wheels
, Article Engineering Failure Analysis ; Vol. 45, issue , October , 2014 , p. 449-455 ; Sharif University of Technology
Abstract
One of the most important issues in railway wheels is residual stresses. It is desirable to produce less residual stresses when possible and to decrease the remaining residual stresses in the wheels. The objective of this paper is to provide an estimation of the residual stresses in the rail wheel caused by the stress field from heat treatment process of a railway wheel. A three-dimensional nonlinear stress analysis model has been applied to estimate stress fields of the railway mono-block wheel in heat treatment process. After forging or casting, railway wheels are heat-treated to induce the desirable circumferential compressive residual stress in the upper rim. Finite element analysis...
Disc size markedly influences concentration profiles of intravenously administered solutes in the intervertebral disc: A computational study on glucosamine as a model solute
, Article European Spine Journal ; Vol. 23, issue. 4 , April , 2014 , p. 715-723 ; Shirazi-Adl, A ; Parnianpour, M ; Urban, J. P. G ; Sharif University of Technology
Abstract
Purpose: Tests on animals of different species with large differences in intervertebral disc size are commonly used to investigate the therapeutic efficacy of intravenously injected solutes in the disc. We hypothesize that disc size markedly affects outcome. Methods: Here, using a small non-metabolized molecule, glucosamine (GL) as a model solute, we calculate the influence of disc size on transport of GL into rat, rabbit, dog and human discs for 10 h post intravenous-injection. We used transient finite element models and considered an identical GL supply for all animals. Results: Huge effects of disc size on GL concentration profiles were found. Post-injection GL concentration in the rat...
Prediction of thermal responses in continuous hot strip rolling processes
, Article Production Engineering ; Vol. 9, issue. 1 , Jul , 2014 , p. 79-86 ; Serajzadeh, S ; Sharif University of Technology
Abstract
Thermal behavior and require power in hot continuous strip rolling are predicted by means of a coupled finite element-upper bound approach. A thermal-finite element analysis is utilized to simultaneously determine temperature distributions within the work-piece and the work-rolls while an upper bound solution is employed at the same time to estimate the rate of heat of deformation and the required power in each rolling stand. The proposed model can be applied for determining thermal behaviors of the strip and the work-rolls in single and multi- pass rolling schedules while the effects of different parameters including initial temperature and rolling speed can be considered in the analysis....
Simulation and experimental analyses of dynamic strain aging of a supersaturated age hardenable aluminum alloy
, Article Materials Science and Engineering A ; Volume 585 , 2013 , Pages 165-173 ; 09215093 (ISSN) ; Karimi Taheri, A ; Kim, H. S ; Sharif University of Technology
2013
Abstract
In this paper, dynamic strain aging (DSA) behavior in a temperature range of (25-235°C) and strain rate range of (10-4-5×10-2s-1) was investigated using a supersaturated age hardenable aluminum alloy. It was found that two mechanisms consisted of pinning of solute atoms to mobile dislocations and dynamic precipitation, were responsible for DSA in the testing conditions. The effects of both mechanisms on the macroscopic flow curve were studied using experimental and improved physically based material modeling approaches. It was shown that both phenomena lead to a negative strain rate hardening in the alloy. Dynamic precipitation acting at high temperature results in considerable work...
Effects of crimping on mechanical performance of nitinol stent designed for femoral artery: Finite element analysis
, Article Journal of Materials Engineering and Performance ; Volume 22, Issue 11 , 2013 , Pages 3228-3236 ; 10599495 (ISSN) ; Sadrnezhaad, S. K ; Sharif University of Technology
2013
Abstract
Nitinol stents are used to minimize improper dynamic behavior, low twistability, and inadequate radial mechanical strength of femoral artery stents. In this study, finite element method is used to investigate the effect of crimping and Austenite finish temperature (A f) of Nitinol on mechanical performance of Z-shaped open-cell femoral stent under crimping conditions. Results show that low A f Nitinol has better mechanical and clinical performance due to small chronic outward force, large radial resistive force, and appropriate superelastic behavior
Unsupported advance length in tunnels constructed using New Austrian Tunnelling Method and ground surface settlement
, Article International Journal for Numerical and Analytical Methods in Geomechanics ; Volume 37, Issue 14 , 2013 , Pages 2170-2185 ; 03639061 (ISSN) ; Ahmadi, M. M ; Hajjar, M ; Kashighandi, A ; Sharif University of Technology
2013
Abstract
Tunnels constructed using New Austrian Tunnelling Method (NATM) are always based on certain round (unsupported) advance lengths, after which, the temporary lining is placed. The settlement of the ground surface resulting from such construction is of high significance in design and practice. The existing data in this respect, however, is scarce. It is the aim of this paper to propose a semi-analytical procedure based on three-dimensional finite element analyses to predict the maximum surface settlement of the ground in NATM tunnels under different combinations of tunnel diameter, overburden depth, round length and soil and lining properties. The comparison of the results with three case...
Seepage investigation of embankment dams using numerical modelling of temperature field
, Article Indian Journal of Science and Technology ; Volume 6, Issue 8 , 2013 , Pages 5078-5082 ; 09746846 (ISSN) ; Noorzad, A ; Ghaemian, M ; Kharaghani, S ; Sharif University of Technology
2013
Abstract
Leakage in embankment dam by applying seepage and thermal numerical simulations are studied in this paper. Unpredicted seepage in earthen dams is known as the main cause of damage in most cases. Determination of seepage flow quantity and prediction of dam leakage is very important. Temperature variation in dam body can be simulated to estimate the water velocity in soil layers. While moving through dam body, seepage flow carries all physical specifications of reservoir water, including its temperature. Mass and energy balance equations are discretized for modeling flow and temperature fields. The finite element method along with a mathematical model has been utilized to discretize and solve...
Excitation shifting: A general low-cost solution for eliminating ultra-low-frequency torque ripple in switched reluctance machines
, Article IEEE Transactions on Magnetics ; Volume 49, Issue 9 , Sept , 2013 , Pages 5135-5149 ; 00189464 (ISSN) ; Davoudi, A ; Kaboli, S ; Edrington, C. S ; Sharif University of Technology
2013
Abstract
Switched reluctance machines (SRMs) suffer from ultra-low-frequency torque ripple in single pulse mode. This ripple is the result of an imbalance in phase currents, when multiphase excitation occurs. This paper investigates the origin of this imbalance and identifies the imbalanced phase. Excitation shifting strategy, which delays excitation of the imbalanced phase, is then proposed. The delay angle adjusts current amplitude in the imbalanced phase to attain a perfect balance between all phases. The excitation shifting strategy is a general solution, which is applicable to both three-phase and four-phase machines. In addition, the proposed method can be implemented by a much simpler drive...