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    The effect of microthread design on magnitude and distribution of stresses in bone: a three-dimensional finite element analysis

    , Article Dental Research Journal ; Volume 15, Issue 5 , 2018 , Pages 347-353 ; 17353327 (ISSN) Golmohammadi, S ; Eskandari, A ; Movahhedy, M. R ; Shirmohammadi, A ; Amid, R ; Sharif University of Technology
    Abstract
    Background: The researches regarding the influence of microthread design variables on the stress distribution in bone and a biomechanically optimal design for implant neck are limited. The aim of the present study is to compare the effect of different microthread designs on crestal bone stress. Materials and Methods: Six implant models were constructed for three-dimensional finite element analysis including two thread profile (coarse and fine) with three different lengths of microthreaded neck (1 mm, 2 mm, and 3 mm). A load of 200 N was applied in two angulations (0° and 30°) relative to the long axis of the implant and the resultant maximum von Mises equivalent (EQV), compressive, tensile,... 

    Effect of centrifugal force on natural frequency of lateral vibration of rotating shafts

    , Article Journal of Sound and Vibration ; Volume 274, Issue 3-5 , 2004 , Pages 985-995 ; 0022460X (ISSN) Behzad, M ; Bastami, A. R ; Sharif University of Technology
    Academic Press  2004
    Abstract
    This paper investigates the effect of shaft rotation on its natural frequency. Apart from gyroscopic effect, the axial force originated from centrifugal force and the Poisson effect results in change of shaft natural frequency. D'Alembert principle for shaft in cylindrical co-ordinate system, along with the stress-strain relation, gives the non-homogenous linear differential equation, which can be used to calculate axial stress in the shaft. Numerical results of this study show that axial stress produced by shaft rotation has a major effect on the natural frequency of long high-speed shafts, while shaft diameter has no influence on the results. In addition, change in lateral natural... 

    Compact basis free relations for stress tensors conjugate to Hill's strain measures

    , Article 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Torino, 4 July 2006 through 7 July 2006 ; Volume 2006 , 2006 ; 0791837793 (ISBN); 9780791837795 (ISBN) Naghdabadi, R ; Asghari, M ; Ghavam, K ; Sharif University of Technology
    American Society of Mechanical Engineers  2006
    Abstract
    If the double contraction of a stress tensor such as T and rate of a Lagrangean strain tensor such as E, i.e. T : Ė produces the stress power then these stress and strain tensors are called a conjugate pair. The applications of the conjugate stress and strain measures are in the development of the basic relations in nonlinear continuum mechanics analysis such as modeling of constitutive equations of elastic-plastic materials. In this paper relations for stress tensors conjugate to an arbitrary Lagrangean strain measure of Hill's class are obtained. The results of this paper are more compact and simpler in compare with those available in the literature. The results are valid for the three... 

    Comparison of periodontally compromised splinted teeth and implant supported fixed partial denture: a three-dimensional finite element analysis on bone response

    , Article Journal of long-term effects of medical implants ; Volume 31, Issue 2 , 2021 , Pages 1-8 ; 19404379 (ISSN) Amid, R ; Kadkhodazadeh, M ; Talebi Ardakani, M. R ; Movahhedy, M. R ; Mirakhori, M ; Hakimi, A ; Broukhim, M ; Sharif University of Technology
    NLM (Medline)  2021
    Abstract
    Introduction - This study aimed to compare the amount and pattern of stress and strain distributed around periodontally compromised splinted teeth and the two-implant abutments supported six-unit fixed partial denture (FPD) using finite element analysis (FEA). Methods and Materials - Six mandibular anterior teeth of a dental model were scanned and the scans were transferred to 3D CAD design and finite element software. Jaw bone was also designed and the teeth were splinted by fiber-reinforced composite (FRC) band. In another model, two implants were placed at the site of canine teeth and a six-unit FPD was designed over them. Models were transferred to finite element software and after... 

    Notch-texture strengthening mechanism in commercially pure titanium thin sheets

    , Article Materials and Design ; Vol. 55, issue , March , 2014 , p. 683-689 Nasiri-Abarbekoh, H ; Abbasi, R ; Ekrami, A ; Ziaei-Moayyed, A. A ; Sharif University of Technology
    Abstract
    Simultaneous effects of notch and texture on strengthening mechanisms of rolled thin sheets of commercially pure titanium were investigated. The presence of notch led to the restriction of deformation systems and different fracture behaviors compared to un-notched specimens. The loss of material's ability to accommodate plastic deformation at the notch tip with increase in rolling reductions changed the notch strengthening phenomenon to the notch weakening one. At medium levels of deformation, due to the simultaneous development of a triaxial stress state and strong basal texture at the notch tip, a new strengthening mechanism which is called "notch-texture strengthening mechanism" led to a... 

    Basis free expressions for the stress rate of isotropic elastic materials in the cases of coalescent principal stretches

    , Article International Journal of Solids and Structures ; Volume 47, Issue 5 , 2010 , Pages 611-613 ; 00207683 (ISSN) Asghari, M ; Sharif University of Technology
    2010
    Abstract
    In this paper, some basis-free expressions for the material time derivative of Lagrangian stress tensors are presented which are generally valid in all cases of coalescent principal stretches. The material is assumed to be elastic and isotropic  

    Endothelial cells morphology in response to combined wss and biaxial cs: introduction of effective strain ratio

    , Article Cellular and Molecular Bioengineering ; Volume 13, Issue 6 , 2020 , Pages 647-657 Pakravan, H. A ; Saidi, M. S ; Firoozabadi, B ; Sharif University of Technology
    Springer  2020
    Abstract
    Introduction: Endothelial cells (ECs) morphology strongly depends on the imposed mechanical stimuli. These mechanical stimuli include wall shear stress (WSS) and biaxial cyclic stretches (CS). Under combined loading, the effect of CS is not as simple as pure CS. The present study investigates the morphological response of ECs to the realistic mechanical stimuli. Methods: The cell population is theoretically studied using our previous validated model. The mechanical stimuli on ECs are described using four parameters; WSS magnitude (0 to 2.0 Pa), WSS angle (− 50° to 50°), and biaxial CS in two perpendicular directions (0 to 10%). The morphology of ECs is reported using four parameters; average... 

    Stretching an anisotropic DNA

    , Article Journal of Chemical Physics ; Volume 128, Issue 12 , 2008 ; 00219606 (ISSN) Eslami Mossallam, B ; Ejtehadi, M. R ; Sharif University of Technology
    2008
    Abstract
    We present a perturbation theory to find the response of an anisotropic DNA to the external tension. It is shown that the anisotropy has a nonzero but small contribution to the force-extension curve of the DNA. Thus an anisotropic DNA behaves like an isotropic one with an effective bending constant equal to the harmonic average of its soft and hard bending constants. © 2008 American Institute of Physics  

    Stress analysis of three-unit all-ceramic dental bridges using FEM

    , Article 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Torino, 4 July 2006 through 7 July 2006 ; Volume 2006 , 2006 ; 0791837793 (ISBN); 9780791837795 (ISBN) Biria, M. J ; Farahmand, F ; Shamsaei, N ; Eslami, G. R ; Sharif University of Technology
    2006
    Abstract
    Mechanical fracture is a common cause of failure for 3-unit dental bridges, particularly, the all-ceramic structures. The purpose of the present study was to evaluate the effect of convergence angles of the abutments on the distribution of the mechanical stresses, within the prosthesis and at the restoration-abutments interface of a 3-unit all-ceramic bridge. The 3-D geometrical data of the second premolar and first and second molar teeth were obtained using ATOS scanner system and utilized for reconstruction of a surface model of the 3-unit bridge in I-Deas as solid modeler software. This was then transferred to MSC/Nastran software for mesh generation and finite element analysis. Two FE... 

    Analysis of Contact Geometry Effect on the Slip Amplitude in Fretting Fatigue of a Turbine Blade Root

    , M.Sc. Thesis Sharif University of Technology Shirzadi, Saba (Author) ; Adibnazari, Saeed (Supervisor)
    Abstract
    Turbine blades are exposed to mechanical and thermal stresses due to their operation in critical conditions and get into various damages such as fatigue and wear. These factors reduce the life of the blades and lead to expensive maintenances. As a result, recognizing the type of possible damage helps to increase the life of the blade and to delay the occurrence of failures by taking the necessary actions.The subject of this thesis is to investigate the effect of geometric parameters on the slip amplitude in the root of a turbine blade. In this work, the effect of three parameters of contact area length, contact angle, and coefficient of friction on relative slip amplitude and contact... 

    Parametric Analysis of Thermomechanical Stresses in Functionally Graded Materials Under in-phase and out-of-phase Loading

    , M.Sc. Thesis Sharif University of Technology Torabi Aliabadi, Amin (Author) ; Abedian, Ali (Supervisor)
    Abstract
    Using Functionally Graded Materials (FGMs) in hot sections of aged aircrafts is one of the most important ways for life extending of Thermal Barrier Coatings (TBCs). Sudden variation of thermal stresses in interface of bond coat and ceramic coat layers could be changed to gradual variation with use of FGMs. The stress in FGMs has been the subject of several researches. Both macro and micromechanical modeling approaches have been used in these studies. In the macro mechanical approach, FGM is modeled as a multi-layer composite in which mechanical properties of each layer is found by averaging the properties and volume fraction of FGM constituents through the thickness of the layer. In this... 

    Numerical Study on Stress Distribution of SolderJoints Based on Solder Microstructure

    , M.Sc. Thesis Sharif University of Technology Zarghami, Mohammad (Author) ; Nourani, Amir (Supervisor)
    Abstract
    In the past, lead-based solders with homogeneous and isotropic behavior were used in microelectronic packages. But today, due to the environmental concerns of lead, lead-free solders have been developed, which consist of a high weight percentage (more than 90%) of tin. Tin crystal shows significant anisotropic behavior, which leads to an anisotropic joint response in miniature solder joints with a small number of grains. In the first part of this research, using the crystal plasticity model, the anisotropic plastic response of tin grain was extracted from bulk solder stress-strain curve, then it was implemented in Abaqus software using built-in Hill's anisotropic plasticity model to consider... 

    Plaque structure affects mechanical stress distribution within blood vessels

    , Article Proceedings of the IASTED International Conference on Biomedical Engineering, BioMed 2014 ; 2014 , pp. 239-243 Mohseni, M ; Mehboudi, N ; Abdollahi, M ; Shamloo, A ; Naghdabadi, R ; Sharif University of Technology
    Abstract
    The main goal of this study is to investigate the effects of plaque structure on its stress distribution. Rupture of plaque causes cerebrovascular diseases which lead to high mortality rates all over the world. Computers are powerful tools to understand the mechanism of plaque rupture. In this study, 3D fluid structure interaction simulation is constructed in ABAQUS 6.13 to clarify the relation between stress distribution of plaque and its structure. A model of common carotid artery with distributed stenosis was chosen for the simulation. To investigate the effects of plaque structure on stress distribution, thickness of fibrous cap and lipid core size were varied in the stenosis.... 

    Thickness as an important parameter in designing vascular grafts

    , Article 2014 21st Iranian Conference on Biomedical Engineering, ICBME 2014 ; Nov , 2014 , p. 40-43 Mohseni, M ; Shamloo, A ; Samani, S. A ; Dodel, M ; Sharif University of Technology
    Abstract
    The main goal of this study is to investigate the role of vascular graft thickness in wall stress gradient in anastomosis region. Atherosclerosis is a common heart disease causes high mortality rates every year. The gold standard treatment of atherosclerosis is replacing with autologous vein extracted from patient's body. Since proper autologous vein is limited, researchers have made efforts to achieve compliance engineered blood vessels. Mechanical stress has great effect on both smooth muscle cells and endothelial cells and it is considered as a stimulus in plaque formation. In this study, we evaluate the role of thickness in wall stress of anastomosis region. For this purpose, two... 

    The influence of grain size and grain size distribution on sliding frictional contact in laterally graded materials

    , Article Mechatronics and Applied Mechanics, Hong Kong, 27 December 2011 through 28 December 2011 ; Volume 157-158 , 2012 , Pages 964-969 ; 16609336 (ISSN); 9783037853801 (ISBN) Khajehtourian, R ; Adibnazari, S ; Tashi, S ; 2011 International Conference; on Mechatronics and Applied Mechanics, ICMAM2011 ; Sharif University of Technology
    2012
    Abstract
    The sliding frictional contact problem for a laterally graded half-plane has been considered. Two finite element (FE) models, in macro and micro scales have been developed to investigate the effective parameters in contact mechanics of laterally graded materials loaded by flat and triangular rigid stamps. In macro scale model, the laterally graded half-plane is discretized by piecewise homogeneous layers for which the material properties are specified at the centroids by Mori-Tanaka method. In micro scale model, functionally graded material (FGM) structure has been modeled as ideal solid quadrant particles which are spatially distributed in a homogeneous matrix. Boundary conditions and... 

    Thickness as an important parameter in designing vascular grafts

    , Article 2014 21st Iranian Conference on Biomedical Engineering, ICBME 2014, 26 November 2014 through 28 November 2014 ; November , 2014 , Pages 40-43 ; 9781479974177 (ISBN) Mohseni, M ; Shamloo, A ; Samani, S. A ; Dodel, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2014
    Abstract
    The main goal of this study is to investigate the role of vascular graft thickness in wall stress gradient in anastomosis region. Atherosclerosis is a common heart disease causes high mortality rates every year. The gold standard treatment of atherosclerosis is replacing with autologous vein extracted from patient's body. Since proper autologous vein is limited, researchers have made efforts to achieve compliance engineered blood vessels. Mechanical stress has great effect on both smooth muscle cells and endothelial cells and it is considered as a stimulus in plaque formation. In this study, we evaluate the role of thickness in wall stress of anastomosis region. For this purpose, two... 

    Nanomedicine applications in orthopedic medicine: State of the art

    , Article International Journal of Nanomedicine ; Volume 10 , 2015 , Pages 6039-6054 ; 11769114 (ISSN) Mazaheri, M ; Eslahi, N ; Ordikhani, F ; Tamjid, E ; Simchi, A ; Sharif University of Technology
    Dove Medical Press Ltd  2015
    Abstract
    The technological and clinical need for orthopedic replacement materials has led to significant advances in the field of nanomedicine, which embraces the breadth of nanotechnology from pharmacological agents and surface modification through to regulation and toxicology. A variety of nanostructures with unique chemical, physical, and biological properties have been engineered to improve the functionality and reliability of implantable medical devices. However, mimicking living bone tissue is still a challenge. The scope of this review is to highlight the most recent accomplishments and trends in designing nanomaterials and their applications in orthopedics with an outline on future directions... 

    Fully coupled analysis of interaction between the borehole and pre-existing fractures

    , Article International Journal of Rock Mechanics and Mining Sciences ; Volume 89 , 2016 , Pages 151-164 ; 13651609 (ISSN) Gomar, M ; Goodarznia, I ; Shadizadeh, S. R ; Sharif University of Technology
    Elsevier Ltd  2016
    Abstract
    The coupling of rock and thermal stresses along with fluid pressure are particularly important in fractured rock masses, since stress-induced changes in permeability can be large and irreversible under perturbations resulting from various natural and induced activities. A new method is presented to model fracture permeability changes during drilling in fractured rocks. The approach includes finite element method (FEM) for fully coupled thermo-poroelastic analysis of stress distribution around borehole and displacement discontinuity method (DDM) to model fracture deformation. Three cases of overbalanced, underbalanced, and balanced drilling fluid pressure conditions are employed. The... 

    A microscopic assessment about the fracture of alumina in the pillbox-type rf window of high-power electron tubes

    , Article IEEE Transactions on Plasma Science ; Volume 49, Issue 4 , April , 2021 , Pages 1414-1421 ; 00933813 (ISSN) Kaboli, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    Alumina is widely used as a vacuum ceramic separator in the pillbox-type output window of high-power electron tubes. The fracture of alumina is one of the most important factors in the failure of these tubes. In this article, the fracture process of alumina in the pillbox-type window of high-power electron tubes is assessed microscopically. The investigation shows the twinning phenomenon in the fractured alumina. The reason for initiating and propagating twins is also investigated. An increase in the alumina temperature decreases the required stress level for generating twins. The overheating condition occurs due to an impedance mismatch in the pillbox-type window. Experimental and numerical... 

    Thermo-mechanical stress analysis of thermal barrier coating system considering thickness and roughness effects

    , Article Surface and Coatings Technology ; Vol. 243 , 2014 , pp. 91-99 ; ISSN: 02578972 Moridi, A ; Azadi, M ; Farrahi, G. H ; Sharif University of Technology
    Abstract
    Cast aluminium-silicon alloy, A356.0, is widely used in automotive and aerospace industries because of its outstanding mechanical, physical, and casting properties. Thermal barrier coatings can be applied to combustion chamber to reduce fuel consumption and pollutions and also improve fatigue life of components. The purpose of the present work is to simulate stress distribution of A356.0 under thermo-mechanical cyclic loadings, using a two-layer elastic-visco-plastic model of ABAQUS. The results of stress-strain hysteresis loop are validated by an out of phase thermo-mechanical fatigue test. Different thicknesses from 300 to 800. μm of top coat and also roughness of the interfaces are...