Sharif Digital Repository

Nowadays, multifunctional two-dimensional (2D) nanostructured materials due to their important role in biomedical and nanotechnological developments have gained the attention of many engineers and scientists with a wide spectrum of disciplines. The present work aims to provide an accurate description of the tensile behavior (from the initial unloaded state through axial strain of about 0.25) of the planar as well as low-buckled stanene and to capture their ideal strength in armchair- and zigzag-directions. Stanene is 2D hexagonal lattice which belongs to D6 hcrystal class having a six-fold rotational symmetry. For an accurate description of anisotropic response of such hyperelastic materials... 

In the recent decades, self-compacting concrete (SCC) has been introduced as high workable concrete that under its own weight and without any impact or vibration fills the framework. Using fibers in concrete was attended by engineers and researchers for decades. These days, fibers were used in bridges, beams, columns, dams, retaining walls and sidewalk. Steel fibers reduce the low tensile strength of concrete and also by bridging between the cracks the absorbed energy of concrete has been increased. Concrete elements can also resist much load, especially impact and explosion load by reinforcing with steel fibers. In past, a lot of researches about using fibers in concrete have been... 

Vibration is one of the most important factors in design, operation and lifetime of drill strings. There for, investigation of vibrations in drill string, like every other rotary machine, is very important. The main goal of this research is developing a nonlinear model for a drill string system dynamics in an inclined well. Effects of drilling mud flow rate, weight on bit, angular velocity along with viscous damping, on the stability and vibration of a drill string are studied. Dynamic equation of the model is developed considering axial displacement and lateral bending geometric nonlinear coupling. The effect of drilling mud flow is modeled using Paidoussis formulations. Equation of motion... 

For the sake of decrease in energy and force of earthquake, seismic isolators are used. Regular seismic isolators are too heavy and damaged by chemical materials, therefore in this research a new approach is used that steel shim plates replaced by carbon and polyamide fibers. The aim of this research is to obtain the dynamic and mechanical properties of carbon and polyamide fiber reinforced isolators in comparison with steel reinforced isolators. In this approach, firstly some specimens have been designed and manufactured, then compresional and cyclic shear tests were carried out on them. All three type isolators are cylindrical and have identical diameter and height. The steel, carbon fiber... 

This thesis contains experimental studies on mechanical properties of adobe and mud material and investigating seismic performance of a conventional adobe house using shake table tests. Mechanical properties of adobe and mud material were studied experimentally based on ASTM and BS standard tests. These experiments were designed to evaluate compressive strength of adobe sun-dried blocks and mud mortar cubes. Besides, shear behavior and tensile bond strength of adobe assemblages were under consideration and shear tests were done on adobe panels. As next part of the research, several shaking table tests were conducted on a dome-roof adobe house as a conventional representative of arch-roof... 

Due to the wide application of lightweight concretes, there have been a lot of research activities in this field. The objectives of these activities have been mainly to increase the strength and endurance, and to reduce the weight and the cost of production of such concretes.
Lightweight concretes, in general, have the following advantages: relatively high strength to density ratio, high thermal and acoustic insulation, and fire resistance. However, foam concretes, as a particular type of lightweight concretes, compared with other types, has the advantage of ease of production. Therefore, in this work various aspects of foam concretes were studied. In this project, using a particular... 

Cyclic Contraction Expansion Extrusion (CCEE) is a new Severe Plastic Deformation (SPD) method used to refine the microstructure and improve mechanical properties of Magnesium AZ91 alloy. In this study, different CCEE process zones are investigated via optical microscopy to understand this process better. The average grain size in the contraction zone decreased to 8.5 microns from an initial value of 106 microns. In the expansion zone, the average grain size was equal to 4.8 microns. Microhardness tests were conducted to study the improvements in mechanical properties. Microhardness of the sample increased from the initial value of 66 HV to 74.4 HV in the contraction zone and 88 HV in... 

Today, tens of millions of people on the planet suffer from heart disease. For the correct diagnosis and treatment of these diseases, there is a vital need for accurate scientific evidence such as various types of vascular and cardiac imaging. One of the applications of guidewires is in cardiovascular imaging. Of course, in addition to diagnosis, this device is also used in the treatment of disease. It should be noted that about 21 million central vessel catheters are performed annually on heart patients, of which about 16 million are performed using the seldinger method. Reportedly, unfortunately, 5% to 19% of these operations have had side effects and harm to the patient or failure.... 

Articular cartilage has limited repair capability following traumatic injuries and current methods of treatment remain inefficient. Reconstructing cartilage provides a new way for cartilage repair and natural polymers are often used as scaffold because of their biocompatibility and biofunctionality. The goal of cartilage tissue engineering is to design a scaffold with proper pore structure and similar mechanical properties to the native tissue. In this study Porous scaffolds prepared from silk fibroin, chitosan and gelatin blends with varying ratio of silk fibroin and gelatin by freeze drying method were characterized for physicochemical, mechanical and biological properties. Among the... 

FE simulations have been widely used to investigate the response of the brain tissue in various circumstances. The accuracy of the material models critically affects the results of the numerical simulation. However, despite the numerous studies aiming for the material modeling of the brain, there is still divergence between the results reported in the literature. A part of this discrepancy is due to the inherent difference between samples. Nonetheless, another part of it is resulted from the differences between testing protocols used by researchers. In some protocols multiple mechanical tests are performed on each sample. Enough recovery time should be considered between consecutive test... 

With increasing awareness, artificial materials have been replaced by recyclable materials and green materials. In the manufacture of composites, natural and degradable materials are also used. The main object of this research is the fabrication of natural fiber reinforced composites. In this research, fibers are used that are cultivated in the country. Also, the effect of fiber length, fiber mass percentage and fiber correction on composite properties was investigated. The fiber length factor is at two levels of 5 mm and 9 mm, the percentage of fiber mass is in four levels of 5%, 10%, 12.5% and 15%, and the factor for correction of fibers is also in two groups of modified fibers and... 

Mechanosensitive membrane channels are indispensable part of cells that sense and respond to mechanical signals. Hence, malfunction of these channels may cause various diseases. Despite numerous studies of these channels, there are still many unanswered questions surrounding these channels and their gating mechanism. Although there have been valuable experimental studies in this field, the need for modelling and computational studies are still felt since experiments face many limitations in this area. Thus, a channel that its crystallographic structure has been recently determined was chosen and studied using computational tools. In this study, gating of the channel under surface tension has... 

Nanocomposites are widely used due to unique properties such as low density and high strength in many industries such as electronics, telecommunications, aerospaces, Petrochemicals and shipbuildings. Meanwhile, due to the importance of economic issues, polymer based nanocomposites are the most used type of nanocomposites. The purpose of this thesis is studing the structural defects of graphene-reinforced nanocomposite polymers on the mechanical properties of these materials. Defects created in nanocomposites can be divided into two categories after construction. The first category is the defects that are created in the graphene structure when it is synthsis, and the second happen at the... 

The properties of metamaterials can be tailored through modification of their microstructures geometry. In this regard, a vast range of metamaterials have been designed. Auxetic metamaterials are a novel class of materials exhibiting the interesting characteristic of negative Poisson’s ratio. Theoretically, auxetic metamaterials have improved mechanical properties such as shear modulus and fracture toughness. The design and modeling of auxetic metamaterials is not completed yet. In order to exploit the interesting properties of auxetic metamaterials, their potential applications have been investigated in medical, sports, automobile and defense industries, so far. In the present work, the... 

Actin is the most abundant protein in most eukaryotic cells. It is highly conserved and participates in more protein-protein interactions than any known protein. Actin plays a crucial role in cell motility, adhesion, morphology and intracellular transport. Its biologically active form is the filament (F-actin), which is assembled from monomeric G-actin. In this thesis, the mechanical properties and characteristics of both G- and F-actin are studied using molecular dynamics simulations. In general, this thesis can be categorized into two individual parts: First, steered molecular dynamics simulation was performed to assess tension of monomeric G-actin molecule, and stress-strain curves were... 

Using materials with better mechanical properties is always advantageous. Many sectors, including automotive and aerospace industries, are always seeking new materials with better mechanical properties and lower weight. A lighter vehicle means lower emission and higher fuel efficiency. Thus, developing new methods to investigate novel materials is very important. One of these novel materials are Metal Matrix NanoComposites (MMNCs). MMNCs are fabricated using nano scale particles embedded in metallic matrix. High strength, stiffness, and hardness are the three most important mechanical properties of MMNCs. Introducing a suitable way of modeling these materials is important since it will... 

Red Blood Cells (RBCs) are the main cells in human blood with a main role in mechanical properties of blood as a fluid. Several methods are developed to simulate the behavior of RBCs motion and deformation in micro-capillaries. Since in microscopic scales, using discrete models are more preferred than continuum methods, moving particle semi-implicit method (MPS) which is one of the recent innovative particle based methods, can simulate micro-fluidic flows based on Navier-Stocks equations. Although by the recent developments MPS method has turned into a considerable tool for modeling blood flow in micro-scales, but still some problems, such as commitment to use small time steps, restrict the... 

Magnesium and its alloys are among the new degradable implants due to their characteristics such as biodegradability, low density, elastic modulus close to bone, and biocompatibility, which have received much attention from researchers. However, in most biological applications, the insufficient corrosion resistance of this alloy causes the accumulation of hydrogen gas around the implant, the loss of mechanical strength and its destruction before the completion of the treatment period. In this research, magnesium base alloys Mg–4Sn, Mg–4Sn–0.2Ag and Mg–4Sn–1Ag are investigated to improve mechanical strength and corrosion resistance. Finally, after casting and alloying, microstructural,... 

In this research, the effects of natural and artificial aging heat treatments on the mechanical and wear behavior of an aluminum alloy from the 7xxx series have been investigated. The study commenced with annealing of the received samples, which were subsequently divided into four categories. One of these categories was placed in a freezer as annealed samples, while the other two underwent artificial aging heat treatments at temperatures of 180 and 210 degrees Celsius. The final category naturally aged over time. As a result, different structures with varied distributions and morphologies of precipitates were formed, and the mechanical properties, mechanisms, and wear resistance of the... 

Electrochemical deposition of multilayer coatings is one of the surface engineering techniques to create thin surface layers with a controlled structure in order to create desirable surface properties. In this research, the nickel-iron-silicon carbide multilayer coating is deposited from a single bath with a sulfate composition and by changing the current density between two values (10 and 40 mA/cm2). The number of layers in multilayer coating was 4, 8, 16, 32.The effect of current density and the number of layers on chemical composition, surface morphology, phase structure, corrosion resistance, nano hardness measurement, wear resistance of multilayer coatings respectively using electron...