Sharif Digital Repository

A new types of architected cellular materials are those with negative poisoon’s ratio named auxetic. This materials indicate unormal behavior under different loads as if they were stretched in one direction, they also expanded in other directions and if pressure is exerted in one direction, they are compressed in all directions. Auxetic materials can improve mechanical properties such as shear strength, strength to weight ratio, thoghness, energy and vibration dissipation and crack expansion due to fatigue.The useful features of this material have been taken into account in a variety of industries, including the automotive industry, in the manufacture of parts such as body and bumper,... 

Unique characteristic behavior of shape memory alloys (SMAs), known as shape memory effect (SME) and superelasticity (SE), make them an appropriate choice for innovative engineering. Design of SMA applications calls for development of constitutive models. To accurately predict SMA behaviors, employing a suitable model with low computational costs is required. In some experimental data, SMAs have coupling in mechanical and thermal behavior. Therefore, mechanical loading changes temperature of the material and variation in temperature affects the mechanical behavior as well. This behavior is called coupled thermo-mechanical effect. In SMA applications, since coupled thermo-mechanical behavior... 

Magnetic shape memory alloys (MSMAs) are a new class of smart materials that exhibit characteristics of large recoverable strains and high frequency. These unique characteristics, make MSMAs interesting materials for applications such as actuators, sensors, and energy harvesters. This thesis presents a three-dimensional phenomenological constitutive model for MSMAs, developed within the framework of irreversible continuum thermodynamics. To this end, a proper set of internal variables is introduced to reflect the microstructural consequences on the material macroscopic behavior. Moreover, a stress-dependent thermodynamic force threshold needed for variant reorientation is introduced which... 

Smart materials are able to change their physical properties under various environmental conditions. Shape memory alloys (SMA) are relatively new smart materials that can respond to environmental stimuli e.g., heat, electricity, etc. Unique behaviors of SMAs, called shape memory effect and superelasticity, have motivated many applications in various fields of study (aerospace, medical, civil engineering, etc.). Although the behavior of SMAs is complicated, modeling and utilizing these materials have been receiving much attention in the past 20 years. Since a cable tolerate more tension than a wire or rod, the shape memory alloy cables could have a broad range of potential applications.... 

Congenital heart defects are a type of heart diseases that some babies get at birth. These diseases generally have symptoms such as shortness of breath, headache, impaired blood supply, hyperplasia of the lungs, enlarged heart, and so on. In the past, open heart surgery was commonly used to treat such diseases, which was a costly and risky procedure. But over time, occluders made it easier. An occluder is referd to a device that is generally minimally invasive in the area of the fault and could block it. The occluders are usually braided type, with inside polyethylene fibers, where tissues can grow and clogs the defect over time. Although occluders have greatly increased the success rate of... 

Porous shape memory alloys (SMAs) were fabricated by many researchers in the last decade and have been initially utilized as bone implants. Also, due to hysteresis in superelastic behavior, and the porous structure, porous SMAs can be used in energy absorbing applications. Such applications call for efficient constitutive modeling of porous SMAs. Moreover, porous SMAs with a wide range of porosity ratios and mechanical properties have been produced in the recent years; therefore, it is necessary to improve the available models and carefully study porous SMA behavior. Different approaches have been utilized for modeling porous SMA behavior. Most of the researchers used homogenization approach... 

Abstract Wire rope isolators are certain types of isolators that due to simplicity of structure and low maintenance costs are taken into consideration in various industries.A variety of different geometries and different features are provided so far that each have their own advantages and disadvantages. The main point is that in all cases they have large-scales. Therefore the usage of them in micro applications is not practical.Shape memory alloys are a class of materials with specific properties such as superelasticity and have inherent hysteresis. It is expected to achieve smaller dimensions suitable for use in micro-applications if they are used in the manufacturing of wire rope... 

Shape Memory alloys are a kind of intelligent materials developed in recent years due to their comprehensive use in medical, robotics, and other advanced sciences. Two main characteristics of them are shape memory effect and superelasticity put these materials in the category of advanced materials. Recently, the new branch of them attracted many studies which is the porous shape memory alloys. The importance of this class of material is related to their properties such as bio-compatibility, superelasticity and shape memory effect. Since shape memory alloys are usually expensive, a new field is developed known as functionally graded porosity distribution. This method is performed by... 

One of the most important tools in industries such as oil, gas, mining and groundwater is inflatable packers. These tools are used for plugging and zonal isolation of a well. The most important member of this cylindrical tool is the elastomer, which is reinforced by metal wire ropes. These cables are placed at an angle relative to the axis of the cylinder and are wound in a helix shape. At both ends of the tool are rings that hold the cylinder. After running the tool into the well and placed in the desired position, by a pipe connected to it, fluid is pumped into it. This increases the diameter or inflation of the tool, and the outer skin of the elastomeric cylinder contacts the well and... 

The current research was conducted to investigate the sealing behavior of single-string and dual-string completion Packer. In order to transfer the oil from reservoir located underground to the surface, the string of tubings is used which is called oil well completion string. A typical completion string not only consists of tubings but also the other facilities such as safety valve, traveling joint, sliding side door and Packer as well. Some reasons including: the cost of drilling and challenges in setting wellhead equipment at some geographical situations, producing more oil and gas lead to extraction oil form more than one zone in the oil well. In addition, taking into the account that,... 

The coronary arteries of the heart are one of the most important arteries in the body's cardiovascular system, which carry oxygen and nutrients to the heart.Therefore, coronary heart disease is one of the most important causes of death in society. In this disease, when the adhesion of sediments and blood plugs to the walls of the arteries increase, the ducts become narrow and the circulatory system gets hard. As a result, the risk of heart attack and mortality increases.Due to the increase in mortality caused by coronary heart disease, working on treatment methods for this disease is important. Angioplasty and stent implantation in a vein are the latest treatments for this disease and have... 

Shape memory alloys (SMAs) are a type of smart materials which have unique features known as pseudo-elasticity, one-way and two-way shape memory eects. The interest in the mechanical behavior of SMAs is rapidly growing with the increasing number of potential industrial applications. The origin of SMA material features is a reversible thermo-elastic martensitic phase transformation between a high symmetry, austenitic phase and a low symmetry, martensitic phase. In most applications, SMAs experience general non-proportional thermo-mechanical loads. Thus, according to experimental observations, the so-called variant reorientation should be considered in the constitutive model development.... 

Elderly falls are one of the leading causes of injury and death to this growing population. In this project, an elderly fall detection system has been designed and built in the form of a wearable device that allows the elderly to be constantly monitored by wearing it continuously. The system hardware is made in the form of a wearable watch that fastens to the left hand of the elderly and continuously monitors the signals of its three sensors, which are accelerometer, gyroscope, and magnetometer. The system continually applies its initial diagnostic method to the signals and sends motion information to a host computer via a wireless connection in the event of a fall. The primary diagnostic... 

Shape memory polymers (SMPs) are a class of multi-phase smart materials that have the ability to return from a deformed to their original shape . The origin of SMP material features is a reversible glassy-rubbery phase transformation between a high stiffness glassy phase and a low stiffness rubbery phase . Thus , according to experimental observations , the phase transformation must be considered in the constitutive model development . In most applications , SMPs experience arbitrary thermo-mechanical loadings . Moreover , SMP structures typically undergo large rotations and strains and the use of a finite deformation scheme is preferred. In this thesis , we study the SMP behavior under... 

Lattice materials with periodic reticulated meso-truss architectures, frequently inspired by nature, are man-made materials offering outstanding stiffness-to-weight ratios which make them an excellent candidate for lightweight structures. Focusing on the metallic pyramidal lattice material for its remarkable applications especially in ultra-light energy absorbers, in the scale of representative volume element (RVE), an analytical framework using beam theory is presented to explore the anisotropic effective elastic properties of this lattice material. Utilizing hollow-tapered struts as the constituent of pyramidal lattices, superior effective stiffness as well as yield strength for the same... 

High-quality online services demand reliable and fast packet delivery at the network layer. However, clear evidence documents the existence of compromised routers in the ISP and enterprise networks, threatening network availability and reliability. A compromised router can stealthily drop, modify, inject, or delay packets in the forwarding path to launch Denial-of-Service, surveillance, man-in-the-middle attacks, etc. So researches tried to create intrusion detection methods to identify adversarial routers and switches. To this end, data-plane fault localization (FL) aims to identify faulty links and is an effective means of achieving high network availability. FL protocols use... 

In this thesis, a numerical analysis of micro chamber filling in centrifugal microfluidics is investigated. In the development of micro total analysis systems, it is often necessary to achieve complete and uniform filling of relatively large micro chambers. With centrifugal devices, these large micro chambers must often be orientated perpendicularly to the direction of centrifugal force and are usually bounded by materials with varying surface properties. On the other hand, the mixing characterization of two fluid by centrifugal microfluidic method has been also conducted. The multiphase flow analyses based on Eulerian-Eulerian approach have been conducted and the VOF method was used for ... 

Confining nematic liquid crystal between two curved boundary conditions while the nematic molecules have a degenerate planar anchoring leads to complex and beautiful textures of molecular disparagement(defect) in the bulk and on the surfaces. Such the liquid crystal shells are made with double-emulsion techniques in microfluidic devices have provided applications for micro-scale colloidal linkers.In this work, we have numerically minimized the elastic energy in one-constant approximation in present of Fournier’s degenerate surface potential with finite element method. The nematic shell is confined between two spherical surfaces that we have studied the final energies and their related... 

Wide applications of elastomeric (rubber-like) materials have led to significant interest of researchers to these materials. Elastomers as a great category of polymeric materials,posses specific properties such as large elastic deformations and energy absorption which make them suitable for aerospace and automotive applications as well as shock and vibration absorbers.In this thesis, an exponential strain energy function (SEF) has been proposed for elastomers which well reproduces the mechanical behavior of these materials and also the material parameters are related to the physical parameters of the material molecular network. This SEF has been concluded from a relation proposed for the...