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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...
3D Bioprinting of oxygenated cell-laden gelatin methacryloyl constructs
, Article Advanced Healthcare Materials ; Volume 9, Issue 15 , 2020 ; Darabi, M. A ; Nasiri, R ; Sangabathuni, S ; Ertas, Y. N ; Alem, H ; Hosseini, V ; Shamloo, A ; Nasr, A. S ; Ahadian, S ; Dokmeci, M. R ; Khademhosseini, A ; Ashammakhi, N ; Sharif University of Technology
Wiley-VCH Verlag
2020
Abstract
Cell survival during the early stages of transplantation and before new blood vessels formation is a major challenge in translational applications of 3D bioprinted tissues. Supplementing oxygen (O2) to transplanted cells via an O2 generating source such as calcium peroxide (CPO) is an attractive approach to ensure cell viability. Calcium peroxide also produces calcium hydroxide that reduces the viscosity of bioinks, which is a limiting factor for bioprinting. Therefore, adapting this solution into 3D bioprinting is of significant importance. In this study, a gelatin methacryloyl (GelMA) bioink that is optimized in terms of pH and viscosity is developed. The improved rheological properties...
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...
Margination and adhesion of micro- and nanoparticles in the coronary circulation: A step towards optimised drug carrier design
, Article Biomechanics and Modeling in Mechanobiology ; Volume 17, Issue 1 , 2018 , Pages 205-221 ; 16177959 (ISSN) ; Shamloo, A ; Sharif University of Technology
Springer Verlag
2018
Abstract
Obstruction of left anterior descending artery (LAD) due to the thrombosis or atherosclerotic plaques is the leading cause of death worldwide. Targeted delivery of drugs through micro- and nanoparticles is a very promising approach for developing new strategies in clot-busting or treating restenosis. In this work, we modelled the blood flow characteristics in a patient-specific reconstructed LAD artery by the fluid–solid interaction method and based on physiological boundary conditions. Next, we provided a Lagrangian description of micro- and nanoparticles dynamics in the blood flow considering their Brownian motion and the particle–particle interactions. Our results state that the number of...
A three-dimensional statistical volume element for histology informed micromechanical modeling of brain white matter
, Article Annals of Biomedical Engineering ; Volume 48, Issue 4 , 2020 , Pages 1337-1353 ; Farahmand, F ; Ahmadian, M. T ; Sharif University of Technology
Springer
2020
Abstract
This study presents a novel statistical volume element (SVE) for micromechanical modeling of the white matter structures, with histology-informed randomized distribution of axonal tracts within the extracellular matrix. The model was constructed based on the probability distribution functions obtained from the results of diffusion tensor imaging as well as the histological observations of scanning electron micrograph, at two structures of white matter susceptible to traumatic brain injury, i.e. corpus callosum and corona radiata. A simplistic representative volume element (RVE) with symmetrical arrangement of fully alligned axonal fibers was also created as a reference for comparison. A...
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 ; 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...
A modified two-surface plasticity model for saturated and unsaturated soils
, Article Indian Geotechnical Journal ; Volume 52, Issue 4 , 2022 , Pages 865-876 ; 09719555 (ISSN) ; Hajitaheriha, M. M ; Hasani Motlagh, A ; Sadeghi, H ; Sharif University of Technology
Springer
2022
Abstract
A modified two-surface critical state plasticity model for saturated and unsaturated soil is presented in this study. The key modification in new model is inclusion of an alternative yield surface used to simulate the behavior of unsaturated soils in addition to corresponding saturated conditions. Moreover, a numerical technique is used to obtain an incremental stress–strain response from loading curves. Modification is applied continuously in each incremental step to return the final stress states and hardening parameters to the yield surface. Results revealed that the adopted modeling approach can predict two independent sets of laboratory unsaturated experiments under various conditions...
A multi-objective approach to optimize the weight and stress of the locking plates using finite element modeling
, Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 236, Issue 2 , 2022 , Pages 188-198 ; 09544119 (ISSN) ; Nourani, A ; Chizari, M ; Sharif University of Technology
SAGE Publications Ltd
2022
Abstract
This paper aims to identify an optimum bone fracture stabilizer. For this purpose, three design variables including the ratio of the screw diameter to the plate width at three levels, the ratio of the plate thickness to the plate width at three levels, and the diameter of the bone at two levels were selected for analysis. Eighteen 3D verified finite element models were developed to examine the effects of these parameters on the weight, maximum displacement and maximum von Mises stress of the fixation structure. Considering the relations between the inputs and outputs using multivariate regression, a genetic algorithm was used to find the optimal choices. Results showed that the diameter of...
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) ; 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...
A validation study of a virtual-based haptic system for endoscopic sinus surgery training
, Article International Journal of Medical Robotics and Computer Assisted Surgery ; Volume 15, Issue 6 , 2019 ; 14785951 (ISSN) ; Khadivar, F ; Abdollahi, E ; Moradi, H ; Farahmand, F ; Sadr Hosseini, S. M ; Vossoughi, G ; Sharif University of Technology
John Wiley and Sons Ltd
2019
Abstract
Background: The development of endoscopic sinus surgery (ESS) training simulators for clinical environment applications has reduced the existing shortcomings in conventional teaching methods, creating a standard environment for trainers and trainees in a more accurate and repeatable fashion. Materials and methods: In this research, the validation study of an ESS training simulator has been addressed. It is important to consider components that guide trainees to improve their hand movements control in the orbital floor removal in an ESS operation. Therefore, we defined three tasks to perform: pre-experiment learning, training, and evaluation. In these tasks, the critical regions introduced in...
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%
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) ; 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...
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) ; 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...
RETRACTED ARTICLE: Design, optimization and experimental evaluation of a novel tactile sensor for large surgical grasper
, Article ICMEE 2010 - 2010 2nd International Conference on Mechanical and Electronics Engineering, Proceedings ; Volume 2 , 2010 , Pages V2111-V2116 ; 9781424474806 (ISBN) ; Shamsollahi, M. J ; Mirbagheri, A ; Farahmand, F ; Sharif University of Technology
IEEE Computer Society
2010
Abstract
There has been a rising trend towards robotic tele-surgery operations in recent years. A major concern, however, is the lack of direct contact between the surgeon and patient's body. Several researchers have proposed various designs of tactile sensors for surgical instruments to improve the dexterity of surgeons. Previously designed sensors, however, are mostly suitable for instruments with small contact areas. In this paper, a novel tactile sensor is introduced in integration with the teeth of a surgical grasper for large organs. It includes strain gauges embedded underneath a toothed plate, which also act as grasping teeth of the jaws of the instrument. The thickness of the plate and the...
On thermomechanical stress analysis of adhesively bonded composite joints in presence of an interfacial void
, Article Composite Structures ; Volume 130 , October , 2015 , Pages 116-123 ; 02638223 (ISSN) ; Yousefsani, S. A ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
This paper deals with analytical thermomechanical stress analysis of adhesively bonded composite joints in presence of a structural imperfection in the form of an interfacial void within the adhesive layer based on the full layerwise theory (FLWT). The joints are subjected to mechanical tension, uniform temperature change, or steady-state heat conduction. The proposed adhesive joint is divided into three distinct regions along its length and a large number of mathematical plies through its thickness. Three sets of fully coupled governing equilibrium equations are derived employing the principle of minimum total potential energy. The three-dimensional nonlinear interlaminar stress...
A viscoelastic model for axonal microtubule rupture
, Article Journal of Biomechanics ; Volume 48, Issue 7 , 2015 , Pages 1241-1247 ; 00219290 (ISSN) ; Manuchehrfar, F ; Rafii Tabar, H ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Axon is an important part of the neuronal cells and axonal microtubules are bundles in axons. In axons, microtubules are coated with microtubule-associated protein tau, a natively unfolded filamentous protein in the central nervous system. These proteins are responsible for cross-linking axonal microtubule bundles. Through complimentary dimerization with other tau proteins, bridges are formed between nearby microtubules creating bundles. Formation of bundles of microtubules causes their transverse reinforcement and has been shown to enhance their ability to bear compressive loads. Though microtubules are conventionally regarded as bearing compressive loads, in certain circumstances during...
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) ; 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...
Relief of edge effects in bi-adhesive composite joints
, Article Composites Part B: Engineering ; Volume 108 , 2017 , Pages 153-163 ; 13598368 (ISSN) ; Tahani, M ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
Three-dimensional thermo-mechanical stress analysis of composite joints with bi-adhesive bonding is presented using the full layerwise theory. Based on three-dimensional elasticity theory, sets of fully coupled governing differential equations are derived using the principle of minimum total potential energy and are simultaneously solved using the state space approach. Results show that bi-adhesive bonding substantially relieves the edge effects. Moreover, series of parametric studies reveal the nonlinear effects of bonding length ratio and the relative stiffness and coefficient of thermal expansion of the mid- and side-adhesives. It is also concluded that the optimum design of a bi-adhesive...