Sharif Digital Repository

Arcs and rings are used extensively in structures such as submarines and bridges due to their particular geometry. On the other hand, in multi-part rocket, due to the high temperature gradients, they form the fastening rings of functional materials (FGM). Considering the importance of this structural element, in this thesis, linear and nonlinear behavior (including bending and post-buckling) of rings made of functionally graded materials under different types of thermo-mechanical loading has been investigated. First, the governing equations are derived from the principle of minimum potential energy, based on the two theorems of Donnell and Love. Donnell's theory equations are solved... 

Tortuosity is an abnormality that may occur in some arteries, such as carotid. It can reduce the blood flow to distal organs, and even in severe cases, causes ischemia and stroke. Tortuosity can be congenital or occurs due to hypertension and reduced axial pre-stretch of artery, in which case called buckling. Since atherosclerotic plaques disrupt the normal pattern of blood flow, and thus make the artery more susceptible to buckling, in this study, the effect of atherosclerotic plaques on arterial stability has been investigated using computational simulation of fluid-structure interaction under pulsatile flow and large deformation. Ideal geometry of normal and atherosclerotic carotid artery... 

In this study, linear and nonlinear mechanical behavior of moderately thick annular sector plates made of functionally graded materials is investigated. In linear analysis, based on first order shear deformation theory, governing equation with two different approaches are derived. In first approach, by application of extended Kantorovich method (EKM), displacements field variables are expressed as separable function of and together, and two sets of ordinary differential equations (ODEs) by using the principle of minimum total potential energy are derived. In the second approach, within FSDT and using the principle of minimum total potential energy, the governing partial differential... 

In this study the free vibration of annular sector plates made of functional materials with using the extended Katrovich method is investigated for a variety of boundary conditions. For this purpose, based on the first order shear deformation theory and Hamilton's principle, equations of motion that they are five differential equations and coupled, are derived. Due to the difficulty of the equations obtained by applying extended kantrovich method on these equations, two ordinary differential equations obtained, the two categories combined fixed and simple boundary conditions will be solved by using generalized differential quadrature and in an iterative process system natural frequency is... 

The aim of this project is buckling and post-buckling analysis of laminated composite circular cylindrical shells under external pressure on the basis of different shell theories. Based on Donnell, Love, and Sanders nonlinear shell theories within the first-order shear deformation model and von Karman geometric nonlinearity, the potential energy of composite circular cylindrical shells under external pressure with simply supported edges is extracted and by minimizing of the total potential energy and implementing the Ritz method, buckling pressure, the nonlinear post-buckling analysis and the curves of static equilibrium paths are presented. Furthermore, the effect of the external energy due... 

Machining of Aluminum Metal Matrix Composites faces different problems including adhesive wear, large machining forces, chatter, poor surface quality and therefore low geometric accuracy etc. due to the fact that a ductile matrix is supporting brittle particles. On of the methods used to reduce such difficulties is vibration assisted machining in which a 10 to 20 micron displacement stimulation is applied to the workpiece or tool during machining process. The effect of this method on the milling of the Al/Sic composite is studied through two separate experiments including one and two dimentional vibration assisted milling respectively. Milling forces, tool wear and surface quality are... 

Problems with composite materials can indicate the lack of mechanical properties of the layers, especially in high temperature, which led to the expansion of functionally graded materials. The most important application of these materials is in high temperature environments .therefore the study of their behavior under mechanical and thermal loads in the range of small and large deformations is very important.The purpose of this research is to provide an analytical solution for nonlinear behavior of functionally graded circular sector plates under thermomechanical load.The material properties are graded through the plate thickness according to a power-law distribution of the volume fraction... 

Coronary arteries often experience tortuosity under internal blood pressure and longitude axial twisting. Arterial tortuosity can enhance the stress concentration on the artery walls. Now if the coronary arteries suffer from atherosclerosis (a common disease among adults) the stress concentration on the tortuous artery plaque will be enhanced as well. Increased stress on the plaque may result in plaque rupture and its consequent damages. This study aims to investigate the stress concentration on the plaques and blood flow patterns within the coronary arteries with plaque. Moreover, the plaque growth was predicted taking into account various geometrical parameters including fibrous cap... 

Blood vessels are subjected to complex mechanical loads, including internal pressure, external pressure, axial stress due to connection to tissues, and the twist caused by movement of the body. The veins and venous valves, which are responsible for returning blood to the heart, become bent and twisted (tortuosity) for various reasons. This venous tortuosity causes valve insufficiency and changes the hemodynamic pattern of blood flow and varicose veins. Studies show that more than a third of old people suffer from varicose veins. These injuries have made it important to study the physical mechanism of venous tortuosity and the function of venous valves.The purpose of this study is to... 

Obtaining the mechanical properties of body tissues in a non-destructive manner is clinically important and has wide applications in the diagnosis and prevention of diseases. one of non-destructive methods is elastography, which requires proper modeling of the tissue and then analysis of the wave propagation in it and obtaining the propagation relations and the dispersion curves. Study of the literature revealed that many simplifications have been used in most modelings of arteries and so far the anisotropy of the artery and its layers with the effects of surrounding tissues and blood have not been studied Therefore, the aim of this study is to model the artery as a two-layer orthotropic... 

Circular cylindrical shells have been widely used in many engineering structures such as spacecraft, submarines, offshores, and storage tanks. Their high stiffness-to-weight ratio and load-carrying capability make them well suited for use in civil and aerospace structures. The consecutive development of material engineering along with the increasing demands for lightweight, heat-resistant, and high strength structures have led to the usage of advanced materials namely functionally graded (FG) materials in designing such structures. In this thesis, the nonlinear static analysis of thin FG cylindrical shells is carried out using the Donnell’s shell theory with first-order approximation and the... 

The steering system is very important in controlling the car. This requires to turning wheels at certain angles. These angles ideally follow the Ackerman geometry. But there is a difference between the real steering angle and the ideal geometry, which caused to steering error. This error depends on two factors, the steering mechanism and the vehicle suspension. Reducing steering error causes to reducing tire wear and increasing vehicle maneuverability at low speeds. In addition, the stability of the vehicle increases when crossing straight line and uneven roads. So far, mechanisms have been designed in accordance with the Ackerman geometry, but in these mechanisms used cam profile. Also... 

In this study non-linear bending of circular sandwich plates with functionally graded (FG) porous core reinforced with graphene nanoplatelets (GPL) is investigated using refined shear deformation theory (RSDT). Displacement field of this theory is considered so that different theories can be introduced to estimate transverse shear strain. Equilibrium equations and boundary conditions are derived using minimum total potential energy principle. The equations are reformulated using potential and stress functions and analytical solution is obtained using perturbation method along with Fourier series. Validations are performed for two cases of linear and non-linear bending of circular plate and... 

Coatings are used in order to prevent wear, corrosion, thermal gradient reduction, surface strength improving and many other applications in industries. One of the common applications of coatings, is to prevent wear and surface abrasion. Hardness and friction coefficients are two parameters that determine the wear properties of a coating. Determining these parameters in very thin films is only possible by nanoindentation and nanoscratch tests. Surface hardness, young modulus and fracture toughness can be obtained using nanoindentation and friction coefficient is calculated from nanoscratch.
Finite element method is widely used for simulating the nanoindentation and nanoscratch... 

Compliant mechanisms are generally used in quasi-static condition and therefore system dynamics do not have a significant effect on their performance; But if the inertia of the links is high, the dynamics of the mechanism will affect its performance altogether. By cleverly designing the mechanism, these effects can be used to create new movement patterns. In this research, a family of compliant mechanisms is introduced whose movement patterns are a function of input speeds. This means that at low speeds, the flexibility of the mechanism does not have a significant effect on its performance, but when the speed exceeds a certain limit, this flexibility changes the configuration of the... 

Cable-driven parallel robots (CDPRs) form a class of robotic manipulator in which the actuation end-effector is transmitted through cables. Due to the unique characteristics and advantages of cable transmission, CDPRs have become increasingly studied in recent years. In this thesis, the study of Geometric Analysis and Dynamic Trajectory of a 5-DOF Cable-Suspended Spatial Parallel Robot is investigated. Geometric analysis is corresponds to the workspace on which the robot is designed. The design of cable mechanisms allows the robot to be used with appropriate configuration in various fields such as industry, medicine, etc. The study of CDPR design has been limited due to several reasons.... 

Based on the modified couple stress and Mindlin plate theories, a Levy type solution is presented for bending and vibration analysis of rectangular isotropic micro plates with simple supports at opposite edges and different boundary conditions at the other two ones. Modified couple stress theory is taken into account to capture the size effect and the governing equations are derived using Hamilton's principle, and solved by Levy solution and space-state method. The results are verified with the existing ones in the literature. As a benchmark, additional tables for vertical deflections and free vibrations of plate with various boundary conditions are presented  

In this study, based on Donnel’s shell theory and the theory of third-order shear deformation, and taking into consideration von Karman non-linearity terms, the analysis of buckling of functionally graded (FG) and multi-layered cylindrical shell with transversely isotropic layers, subjected to different loadings, was done. Along this line, first using the principle of minimum total potential energy, and based on the Donnel’s shell theory and the theory of third-order shear deformation, five couple equilibrium equations for cylindrical shell were produced. Next these five coupled equilibrium equations were reduced to three uncoupled equilibrium equation which are, in terms of transverse... 

Nowadays, Eye injuries caused by blunt impacts are considered among the major causes of blindness and vision problems; therefore, studying the existence of possible damages can be quite useful and effective. One of the quickest and most suitable methods in identifying damage parameters is finite-element modeling of the human eye. In this regard, in the current study, first a geometrical design was created by incorporating CT-Scan images of the eye into Mimics and later Solid works software. Afterwards, the most suitable mechanical properties for the constituents of the eye were extracted from the literature. The mechanical properties of vitreous and Sclera were obtained by experimental... 

Tire is one component of the suspension system and has beneficial effects on reducing vibrations caused to the vehicle. This study aims to determine the factors affecting the damping and stiffness of the tire is carried out. The modeling of factors were identified. For testing the modeling effort is to be made to the instruments used to measure the damping and stiffness of the tires. To make the structural static analysis, dynamic and modal was to have sufficient structural strength and the displacements and stresses are sensibly placed. Factors that have influence on the hardness of the ring diameter, the outer diameter of the tire, tire pressure, tire tread depth, tire wall thickness,...