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mechanical-stress
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Analysis of Contact Geometry Effect on the Slip Amplitude in Fretting Fatigue of a Turbine Blade Root
, M.Sc. Thesis Sharif University of Technology ; 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 ; 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 ; 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...
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 ; 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...
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 ; 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....
Notch-texture strengthening mechanism in commercially pure titanium thin sheets
, Article Materials and Design ; Vol. 55, issue , March , 2014 , p. 683-689 ; 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...
Thickness as an important parameter in designing vascular grafts
, Article 2014 21st Iranian Conference on Biomedical Engineering, ICBME 2014 ; Nov , 2014 , p. 40-43 ; 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...
Tissue growth into three-dimensional composite scaffolds with controlled micro-features and nanotopographical surfaces
, Article Journal of Biomedical Materials Research - Part A ; Volume 101, Issue 10 , 2013 , Pages 2796-2807 ; 15493296 (ISSN) ; Simchi, A ; Dunlop, J. W. C ; Fratzl, P ; Bagheri, R ; Vossoughi, M ; Sharif University of Technology
2013
Abstract
Controlling topographic features at all length scales is of great importance for the interaction of cells with tissue regenerative materials. We utilized an indirect three-dimensional printing method to fabricate polymeric scaffolds with pre-defined and controlled external and internal architecture that had an interconnected structure with macro- (400-500 μm) and micro- (∼25 μm) porosity. Polycaprolactone (PCL) was used as model system to study the kinetics of tissue growth within porous scaffolds. The surface of the scaffolds was decorated with TiO2 and bioactive glass (BG) nanoparticles to the better match to nanoarchitecture of extracellular matrix (ECM). Micrometric BG particles were...
Trunk muscle fatigue and its implications in EMG-assisted biomechanical modeling
, Article International Journal of Industrial Ergonomics ; Volume 43, Issue 5 , 2013 , Pages 425-429 ; 01698141 (ISSN) ; Mirka, G.A ; Sharif University of Technology
2013
Abstract
Muscle fatigue affects the underlying EMG-force relationship on which EMG-assisted biomechanical models rely. The aim of this study was to evaluate the impact of short duration muscle fatigue on the muscle gain value. Participants performed controlled, isometric trunk extension exertions at 10, 20, and 30 degrees of trunk flexion and controlled isokinetic trunk extension exertions at 5 and 15°/sec on five separate days. Fatigue of the lumbar extensors was generated by moderate-intensity, trunk extension exertions. Participants performed controlled test contractions at defined intervals throughout the fatiguing bout and the EMG activities of trunk muscles were collected. These EMG data were...
Analysis of different material theories used in a FE model of a lumbar segment motion
, Article Acta of Bioengineering and Biomechanics ; Volume 15, Issue 2 , 2013 , Pages 33-41 ; 1509409X (ISSN) ; Nikkhoo, M ; Haghpanahi, M ; Parnianpour, M ; Sharif University of Technology
2013
Abstract
In this study, a nonlinear poroelastic model of intervertebral disc as an infrastructure was developed. Moreover, a new element was defined consisting a disc (Viscoelastic Euler Beam Element) and a vertebra (Rigid Link) as a unit element. Using the new element, three different viscoelastic finite element models were prepared for lumbar motion segment (L4/L5). Prolonged loading (short-term and long-term creep) and cyclic loading were applied to the models and the results were compared with results of in vivo tests. Simplification of the models by using the new element leads to reduction of the runtime of the models in dynamic analyses to few minutes without losing the accuracy in the results
A meta-model analysis of a finite element simulation for defining poroelastic properties of intervertebral discs
, Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 227, Issue 6 , 2013 , Pages 672-682 ; 09544119 (ISSN) ; Hsu, Y. C ; Haghpanahi, M ; Parnianpour, M ; Wang, J. L ; Sharif University of Technology
2013
Abstract
Finite element analysis is an effective tool to evaluate the material properties of living tissue. For an interactive optimization procedure, the finite element analysis usually needs many simulations to reach a reasonable solution. The metamodel analysis of finite element simulation can be used to reduce the computation of a structure with complex geometry or a material with composite constitutive equations. The intervertebral disc is a complex, heterogeneous, and hydrated porous structure. A poroelastic finite element model can be used to observe the fluid transferring, pressure deviation, and other properties within the disc. Defining reasonable poroelastic material properties of the...
An analytical approach to study the intraoperative fractures of femoral shaft during total hip arthroplasty
, Article Journal of Biomechanical Engineering ; Volume 135, Issue 4 , 2013 ; 01480731 (ISSN) ; Farahmand, F ; Shodja, H. M ; Samadi Dooki, A ; Sharif University of Technology
2013
Abstract
An analytical approach which is popular in micromechanical studies has been extended to the solution for the interference fit problem of the femoral stem in cementless total hip arthroplasty (THA). The multiple inhomogeneity problem of THA in transverse plane, including an elliptical stem, a cortical wall, and a cancellous layer interface, was formulated using the equivalent inclusion method (EIM) to obtain the induced interference elastic fields. Results indicated a maximum interference fit of about 210 μm before bone fracture, predicted based on the Drucker-Prager criterion for a partially reamed section. The cancellous layer had a significant effect on reducing the hoop stresses in the...
Tool-tissue force estimation in laparoscopic surgery using geometric features
, Article Studies in Health Technology and Informatics ; Volume 184 , 2013 , Pages 225-229 ; 09269630 (ISSN) ; Behzadipour, S ; Farahmand, F ; Sharif University of Technology
IOS Press
2013
Abstract
This paper introduces three geometric features, from deformed shape of a soft tissue, which demonstrate good correlation with probing force and maximum local stress. Using FEM simulation, 2D and 3D model of an in vivo porcine liver was built for different probing tasks. Maximum deformation angle, maximum deformation depth and width of displacement constraint of the reconstructed shape of the deformed body were calculated. Two neural networks were trained from these features and the calculated interaction forces. The features are shown to have high potential to provide force estimation either for haptic devices or to assess the damage to the tissue in large deformations of up to 40%
Effect of microthread design of dental implants on stress and strain patterns: A three-dimensional finite element analysis
, Article Biomedizinische Technik ; Volume 58, Issue 5 , September , 2013 , Pages 457-467 ; 00135585 (ISSN) ; Raoofi, S ; Kadkhodazadeh, M ; Movahhedi, M. R ; Khademi, M ; Sharif University of Technology
Walter de Gruyter and Co
2013
Abstract
The aim of this study was to use finite element analysis (FEA) to assess the influence of microthread design at the implant neck on stress distribution in the surrounding bone. A commercially available implant with 3.5 mm diameter and 10.5 mm length was selected and used as a model. For the purpose of designing the microthread implant model, microthreads were added to the implant neck in a computerized model. A force measuring 100 N was then applied to the entire surface of the abutment in the vertical direction. The results showed that in both models, stress was mainly concentrated at the cortical bone adjacent to the neck of the implant. Maximum stress values in the cortical bone...
High-temperature deformation and structural restoration of a nanostructured Al alloy
, Article Scripta Materialia ; Volume 66, Issue 11 , 2012 , Pages 911-914 ; 13596462 (ISSN) ; Simchi, A ; Kim, H. S ; Sharif University of Technology
2012
Abstract
We studied the flow stress and microstructural changes of nanostructured Al-6063 alloy produced by mechanical alloying at various temperatures and strain rates. The analysis of flow curves was performed by a constitutive equation, and the stress exponent and activation energy were determined as functions of strain. The deformation mechanisms were elaborated through microstructural observations by electron backscattering diffraction and transmission electron microscopy. Coarsening of the subgrains and grain growth upon deformation was monitored and related to the Zener-Hollomon parameter
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) ; 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...
A model for evaluating thermo-mechanical stresses within work-rolls in hot-strip rolling
, Article Journal of Engineering Mathematics ; Volume 72, Issue 1 , 2012 , Pages 73-85 ; 00220833 (ISSN) ; Serajzadeh, S ; Sharif University of Technology
Abstract
A mathematical model is proposed for the determination of the thermo-mechanical stresses in work-rolls during hot-strip rolling. The model describes the evolution of the temperature fields in the work-roll and in the work-piece, and in the latter the plastic heat generation is taken into account. The frictional heat generated on the contact surface is also included. The problem is treated in two steps. First, a numerical method is developed for the analysis of the coupled thermal problem of the temperature distributions within the work-roll and metal being rolled, while an admissible velocity field is employed to estimate the heat of deformation. In the second step, the finite-element method...
Multi-layered nature of the wall of the carotid-artery bifurcation on hemodynamic and mechanical stress and strain
, Article 2011 18th Iranian Conference of Biomedical Engineering, ICBME 2011 ; 2011 , Pages 84-89 ; 9781467310055 (ISBN) ; Firoozabadi, B. D ; Sharif University of Technology
Abstract
Arterial diseases, namely atherosclerosis, are believed to be a product of abnormal changes in both hemodynamic and non-hemodynamic factors. In order to explornmk,e the role of different factors in initiation and progression of this disease, a CFD technique was applied to study Interaction between the structure of the artery and blood flow for different suggested models that were used to describe mechanics of vessel wall. This study presents a three-dimensional, steady state simulation of blood flow through the single and double layered carotid artery bifurcation using fluid structure interaction (FSI) method. The wall shear stress and mechanical stress/strain are computed and analyzed under...
Dynamic parameters of saturated and unsaturated sand at different ranges of shear strain levels in cyclic simple shear tests
, Article 14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering ; 2011 ; Golshan, Z ; Sharif University of Technology
2011
Abstract
In order to evaluate dynamic properties of Babolsar and Toyoura sands at saturation levels of 25, 50, 75 & 100%, a series of cyclic simple shear tests were carried out. The SGI type cyclic simple shear device was used to study the shear modulus, G, and damping ratio, D, of the above mentioned sands at cyclic shear strain of 0.5, 5 & 10%. The effect of degree of saturation (S), vertical consolidation stress (σ vc) and number of loading cycles (N) were investigated. On the basis of the tests results, the shear modulus approximately remains constant by change of degree of saturation from 25 to 50% and decreases when reaches the degree of saturation 75%. Damping ratio approximately is constant...
Temperature and thickness effects on thermal and mechanical stresses of rotating FG-disks
, Article Journal of Mechanical Science and Technology ; Volume 25, Issue 3 , 2011 , Pages 827-836 ; 1738494X (ISSN) ; Azadi, M ; Sharif University of Technology
Abstract
In the present paper, radial and hoop thermal and mechanical stress analysis of a rotating disk made of functionally graded material (FGM) with variable thickness is carried out by using finite element method (FEM). To model the disk by FEM, one-dimensional two-degree elements with three nodes are used. It is assumed that the material properties, such as elastic modulus, Poisson's ratio and thermal expansion coefficient, are considered to vary using a power law function in the radial direction. The geometrical and boundary conditions are in the shape of two models including thermal stress (model-A) and mechanical stress (model-B). In model-A there exists no pressure in both external and...