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    Finite element model of SWCNT under hydrostatic pressure

    , Article AIP Conference Proceedings, 10 April 2007 through 12 April 2007, Sharjah ; Volume 929 , 2007 , Pages 82-88 ; 0094243X (ISSN) ; 0735404399 (ISBN); 9780735404397 (ISBN) Sakhaee Pour, A ; Ahmadian, M. T ; Sharif University of Technology
    A finite element technique is used to mimic radial deformation of single-walled carbon nanotubes under hydrostatic pressure. The elastic deformation of nanotubes is modeled via elastic beams. Properties of the beam element are evaluated by considering characteristics of the covalent bonds between the carbon atoms in a hexagonal lattice. Applying the beam model in a three dimensional space, the elastic properties of the nanotube in the transverse direction are evaluated. The effects of diameter and wall thickness on the radial and circumferential elastic moduli of zigzag and armchair nanotubes are considered. Results are in good agreement with molecular structural mechanics data in the... 

    Dynamic and Vibration Analysis of Wavy Carbon Nanotube-Reinforced Composites

    , M.Sc. Thesis Sharif University of Technology Shafiee Motahar, Mohammad (Author) ; Ahmadiyan, Mohammad Taghi (Supervisor) ; Asghari, Mohsen (Supervisor)
    Characterization and simulation of carbon nanotube-reinforced composites at large scale have been a concern of researchers in the past decade. This is due to the computational complication of considering many embedded carbon nanotubes (CNTs). However a simple meshing of organized CNT distribution in the matrix can ease this obstacle. In this study, a finite element approach is employed to investigate the elastodynamic behavior of a wavy CNT-reinforced composite structure. A three dimensional structure with up to 6400 uniformly distributed wavy CNTs is embedded in a polymer matrix. Each wavy nanotube is represented by a set of beam elements. The effect of nanotube waviness and volume fraction... 

    Experimental Study of the Mechanical Behavior of Plastic Concrete Cutoff Walls

    , M.Sc. Thesis Sharif University of Technology Mousavi, Hamed (Author) ; Jafarzadeh, Fardin (Supervisor)
    The seepage through foundation of earth dams causes the serious menaces and the reduction in their efficiency. Therefore essential contrivances must be provided against mentioned problem. One of the common and efficient ways to control the seepage through pervious layers under earth dams is plastic concrete cut off wall which is used as a filling material in dam foundation due to the low permeability, plastic behavior and low enough elastic modulus compatible with the adjusted soil. In addition to the mentioned properties, it is important that plastic concrete have an adequate compressive strength to sustain the lateral and vertical loads. Since the change in the ratio W/C (water to cement)... 

    Production of Porous Ti and Ti-26Nb-1Si Via Powder Metallurgy Method andInvestigation Some of Their Physical and Mechanical Properties

    , M.Sc. Thesis Sharif University of Technology Zamani, Mohammad Hasan (Author) ; Abachi, Parvin (Supervisor) ; Ziaei Moayyed, Ali Akbar (Supervisor)
    Porous titanium and titanium alloys products are proper to use as implants which because of good properties such as high corrosion resistance, good biocompatibility, high strength to weight ratio and low elastic modulus. Porosity induces a decrease in elastic modulus and an increase of bioactivity. In present work, porous specimens of pure titanium and Ti-26Nb-1Si alloy were produced via conventional powder metallurgy route by applying low pressure. The influence of TiH2 Powder addition on some physical and mechanical properties of samples was investigated. The amount of TiH2 powder was used in the range of 0-40 weight percent. The powders were firstly mixed for 3 hours and then compacted... 

    Influence of Polystyrene on Behavior of Light-Weight Concrete

    , M.Sc. Thesis Sharif University of Technology Rezaei, Mohammad (Author) ; Khaloo, Alireza (Supervisor) ; Kazemi, Mohammad Taghi (Supervisor)
    Normal aggregates are replaced by polystyrene beads (EPS) due to their low unit weight. EPS concrete is known for its low density and environmentally friendly properties apart from having various pros such as better heat and sound isolation, affordability, and ease of construction. EPS grain size can also affect the compressive strength, and the tensile strength of EPS concrete compression is also inversely related to EPS grain diameter. The EPS concrete has four different percentages of EPS; 0%, 25%, 50%, and 75%. Each EPS percentage has six different unit weights; 15,20,25,30,35 and 40 kg/m3. In the present study 19 different types of mixing designs were used, the one with no EPS beads has... 

    Design of a 4 DOF laparoscopic surgery robot for manipulation of large organs

    , Article Studies in Health Technology and Informatics ; Volume 173 , 2012 , Pages 8-12 ; 09269630 (ISSN) ; 9781614990215 (ISBN) Alamdar, A ; Mirbagheri, A ; Farahmand, F ; Durali, M ; Sharif University of Technology
    In this paper, a 4-DOF robotic arm for tool handling in laparoscopic surgery is introduced. The robot provides sufficient force to handle endoscopic tools used for large organ manipulation and is capable of measuring the tool-tissue forces. The RCM constraint is achieved using a spherical mechanism and roll and insertion motions are provided using time pulley and spindle-drive, respectively. The forward and inverse kinematics of the robot was solved and the dimensions of its links were determined, using particle swarm optimization method, so that the maximum kinematic and dynamic performance could be achieved  

    A new model for the effect of grain size on the elastic modulus of nanocrystalline materials

    , Article Materials Science- Poland ; Volume 27, Issue 1 , 2009 , Pages 279-285 ; 01371339 (ISSN) Ali Shafiei, M ; Sharif University of Technology
    A new model is developed for the structure of nanocrystalline materials. Based on the developed model, a new approach for investigating the effect of grain size on the elastic moduli of nanocrystalline materials is introduced. The predictions of the model are strongly correlated with the experimental results reported in the existing literature  

    Effect of nano Al2O3 addition on mechanical properties and wear behavior of NiTi intermetallic

    , Article Materials and Design ; Volume 51 , October , 2013 , Pages 375-382 ; 02613069 (ISSN) Farvizi, M ; Ebadzadeh, T ; Vaezi, M. R ; Kim, H. S ; Simchi, A ; Sharif University of Technology
    Elsevier Ltd  2013
    It has been found that the high wear resistance of NiTi alloy is mainly attributed to its pseudoelasticity which is only effective within a small temperature range. It is believed that pseudoelasticity becomes ineffective by applying high-load wear condition which yields plastic deformation and temperature increment during wear test. Therefore, the enhanced wear resistance can be obtained from the improvement of mechanical property of the alloy without much reduction of pseudoelasticity. In this study, a low weight percentage of hard Al2O3 nanoparticles were added to NiTi atomized powders. The resultant powder mixture was homogenized by ball milling and sintered in a vacuum furnace in order... 

    A meshless EFG-based algorithm for 3D deformable modeling of soft tissue in real-time

    , Article Studies in Health Technology and Informatics, 9 February 2012 through 11 February 2012 ; Volume 173 , February , 2012 , Pages 1-7 ; 09269630 (ISSN) ; 9781614990215 (ISBN) Abdi, E ; Farahmand, F ; Durali, M ; Sharif University of Technology
    The meshless element-free Galerkin method was generalized and an algorithm was developed for 3D dynamic modeling of deformable bodies in real time. The efficacy of the algorithm was investigated in a 3D linear viscoelastic model of human spleen subjected to a time-varying compressive force exerted by a surgical grasper. The model remained stable in spite of the considerably large deformations occurred. There was a good agreement between the results and those of an equivalent finite element model. The computational cost, however, was much lower, enabling the proposed algorithm to be effectively used in real-time applications  

    Effect of specimen's age on mechanical properties of plastic concrete walls in dam foundations

    , Article Electronic Journal of Geotechnical Engineering ; Volume 17 D , 2012 , Pages 473-482 ; 10893032 (ISSN) Jafarzadeh, F ; Mousavi, S. H ; Sharif University of Technology
    According to available information and references, water leakage and internal erosion in bodies and foundations of embankment dams are the main reasons of many problems and failures. To reduce this risk in foundation, plastic cut off walls is one of the most reliable solutions. In this research the effect of specimen's age on the mechanical properties of plastic concrete was studied. This paper summarizes the test results which were conducted in unconfined and triaxial state. Plastic concrete specimens were prepared in the laboratory condition using the materials provided from the Silve dam site. Test results have shown that the time and confining pressure extremely affect the mechanical... 

    Contribution of ordered-inordered phenomenon within the interphase region toward increasing elastic modulus in CNT/polymer nanocomposites

    , Article Materials Science and Technology Conference and Exhibition 2015, MS and T 2015, 4 October 2015 through 8 October 2015 ; Volume 1 , October , 2015 , Pages 595-602 ; 9781510813939 (ISBN) Shayesteh Zeraati, A ; Goodarzi Hosseinabadi, H ; NACE International ; Sharif University of Technology
    Association for Iron and Steel Technology, AISTECH  2015
    Exceptional mechanical properties of carbon nanotubes (CNTs) such as high elastic modulus, stiffness and tensile strength have made them as promising reinforcement in polymer nanocomposite systems. The characteristics of CNTs/polymer interphase region directly affect the efficiency of nanotubes for improving the nanocomposite mechanical properties. In this work, the influence of chains alignment within the interphase region on elastic response of the nanocomposite is assessed using a novel ordered-inordered approach. The applicability of the presented approach is examined by implementing the approach on a series of reported data available in the literature. The effects of CNT content,... 

    An ellipsoidal model for studying response of head impacts

    , Article Acta of Bioengineering and Biomechanics ; Volume 12, Issue 1 , 2010 , Pages 47-53 ; 1509409X (ISSN) Heydari, M ; Jani, S ; Sharif University of Technology
    The objective of this study was to propose a new analytical model for studying response of head impacts. Head is modeled by fluidfilled ellipsoidal shell of inconstant thickness impacted by a solid elastic sphere. Modeling the head as an ellipsoid is more realistic than modeling it as a sphere, the previous model existing in the literature [3]-[8]. In this model, the effect of Hertzian contact stiffness and local shell stiffness are combined to derive explicit equations for impact duration, the peak force transmitted to head, and the head injury criterion. One of the advantages of the model presented is sensitivity to the site of impact. A comparison between the present analytical results... 

    Fabrication mechanism of nanostructured HA/TNTs biomedical coatings: an improvement in nanomechanical and in vitro biological responses

    , Article Journal of Materials Science: Materials in Medicine ; Volume 27, Issue 10 , 2016 ; 09574530 (ISSN) Ahmadi, S ; Riahi, Z ; Eslami, A ; Sadrnezhaad, S. K ; Sharif University of Technology
    Springer New York LLC  2016
    In this paper, a mechanism for fabrication of nanostructured hydroxyapatite coating on TiO2 nanotubes is presented. Also, the physical, biological, and nanomechanical properties of the anodized Ti6Al4V alloy consisting TiO2 nanotubes, electrodeposited hydroxyapatite, and the hydroxyapatite/TiO2 nanotubes double layer coating on Ti6Al4V alloy implants are compared. Mean cell viability of the samples being 84.63 % for uncoated plate, 91.53 % for electrodeposited hydroxyapatite, and 94.98 % for hydroxyapatite/TiO2 nanotubes coated sample were in the acceptable range. Merely anodized prototype had the highest biocompatibility of 110 % with respect to the control sample. Bonding strength of... 

    Molecular dynamics study on axial elastic modulus of carbon nanoropes

    , Article Archives of Civil and Mechanical Engineering ; Volume 19, Issue 4 , 2019 , Pages 1127-1134 ; 16449665 (ISSN) Mehralian, F ; Firouz Abadi, R. D ; Norouzi, M ; Sharif University of Technology
    Elsevier B.V  2019
    Carbon nanoropes (CNRs) are of interest for a wide variety of nanotechnological applications. Since little attention has been paid to mechanical properties of CNRs, their axial elastic modulus is explored herein. Molecular dynamics (MDs) simulations are adopted for analysis of Young's modulus of CNRs. It is also shown that increase in the initial helical angle decreases Young's modulus; however, by increase in the number of CNTs and strands, different influence on Young's modulus emerges. Therefore, the highest value of Young's modulus obtained at the lower value of initial helical angle and consequently, Young's modulus of bundle of straight CNTs is higher than CNRs with hierarchical... 

    Fabrication and evaluation of a bilayer hydrogel-electrospinning scaffold prepared by the freeze-gelation method

    , Article Journal of Biomechanics ; Volume 98 , 2020 Kamali, A ; Shamloo, A ; Sharif University of Technology
    Elsevier Ltd  2020
    This study presents a bilayer structure as a skin scaffold comprised of an electrospun sheet layer made of polycaprolactone and polyvinil alcohol and a porous hydrogel layer made of chitosan and gelatin. The hydrogel layer was fabricated by employing the freeze-gelation technique. The bilayer structure was achieved by pouring the hydrogel solution on the electrospun sheet at the bottom of a mold followed by the freeze-gelation technique to obtain a porous structure in the hydrogel. The hydrogel and hydrogel-electrospun samples were characterized by scanning electron microscopy, swelling, tensile strength, in vitro and in vivo analyses. From a mechanical strength standpoint, the combination... 

    Design of Fillet Welds in Plastic State

    , M.Sc. Thesis Sharif University of Technology Yazdi, Mohammad Hassan (Author) ; Maleki, Shervin (Supervisor)
    Fillet welds are widely used in steel construction due to their high strength and economy. In the joints used in construction, eccentricity loads in complex weld stress. The current research involves 72 bending specimens and 16 torsion specimens being modeled to study different design code relationships regarding the plastic properties of welds. In line with an even comprehensive study, the previous experimental programs in this field have been added to the modeling results.Reliability analysis has been applied to examine code relationships more precisely. The analysis involved examination of various uncertainties which showed that applying elastic methods proves more conservative than other... 

    Behavior of Composites Containing Multi-coated Nano-fibers with Interfacial Damage in Couple Stress Theory

    , Ph.D. Dissertation Sharif University of Technology Hashemian, Behdad (Author) ; Mohammadi Shodja, Hossein (Supervisor)
    It is well-known that classical continuum theory has certain deficiencies in capturing the size effects and predicting the nanoscopic behavior of materials in the vicinity of nano-inhomogeneities and nano-defects with reasonable accuracy. Couple stress theory which is associated with an internal length scale for the medium is one of the higher order continuum theories capable of overcoming such difficulties. Since most reinforcements may not be perfectly bonded to their surrounding matrix, the perfect bonding condition is often inadequate in describing the physical and mechanical behavior of real composite materials. In this work, the problem of a nano-size fiber embedded in an unbounded... 

    Damage assessment of a concrete arch dam through nonlinear incremental dynamic analysis

    , Article Soil Dynamics and Earthquake Engineering ; Volume 44 , January , 2013 , Pages 127-137 ; 02677261 (ISSN) Alembagheri, M ; Ghaemian, M ; Sharif University of Technology
    Damage assessment of concrete arch dams is carried out through nonlinear Incremental Dynamic Analysis (IDA) of a typical arch dam. In this study the Morrow Point arch dam is subjected to a set of 12 three-component earthquakes each scaled to 12 increasing intensity levels. The dam-foundation interaction effects have been investigated by varying foundation's modulus of elasticity to be equal and half of dam concrete's modulus of elasticity. Damage propagation through the dam body is investigated and various IDA curves are created. The performance and various limit-states of the dam structure are examined based on the obtained results. Simple damage indices are proposed through comparison of... 

    Effects of surface residual stress and surface elasticity on the overall yield surfaces of nanoporous materials with cylindrical nanovoids

    , Article Mechanics of Materials ; Volume 51 , 2012 , Pages 74-87 ; 01676636 (ISSN) Moshtaghin, A. F ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
    Elsevier  2012
    Mechanical properties of a material near the surfaces and interfaces are different from those of the same material far from the surfaces/interfaces. The effect of this difference on the effective mechanical properties of heterogeneous materials becomes significant when the size of inhomogeneities is at the scale of nanometers. In this article, within a micromechanical framework, the effects of surface residual stress and surface elasticity are taken into account to obtain a macroscopic size-dependent yield function for nanoporous materials containing aligned cylindrical nanovoids. Based on the modified Hill's condition, the strains are decomposed into two parts, a part due to the external... 

    A combined first principles and analytical treatment for determination of the surface elastic constants: Application to Si(001) ideal and reconstructed surfaces

    , Article Philosophical Magazine Letters ; Volume 92, Issue 1 , Sep , 2012 , Pages 7-19 ; 09500839 (ISSN) Ojaghnezhad, F ; Shodja, H. M ; Sharif University of Technology
    Behavior of nanostructures, which are characterized by a large surface-to-volume ratio, is greatly influenced by their surface parameters, such as surface elastic moduli tensor. Accurate determination of the surface elastic constants by first principles is of particular interest. To this end, through consideration of the fundamental thermodynamic arguments for free solid surfaces, an analytical formulation for the change in specific Helmholtz surface free energy is developed. Relating this formulation to the corresponding energy calculated via first principles leads to the determination of the surface elastic moduli tensor. The surface mechanical properties, namely surface energy, surface...