Sharif Digital Repository

There are experimental observations that show material response in micro-scale is dependent on some other parameters rather than Lame parameters. Strain gradient elasticity has been recently developed to take into account this characteristic of materials response. In strain gradient elasticity, characteristic length parameters enter the constitutive equations through the elastic strain energy density function. The elastic strain energy density function is assumed to be a function of the gradient of strain tensor in addition to the strain tensor. In this way, new material constant (characteristic length parameters) are introduced and entered into the constitutive equations. In recent years,... 

Thermal barrier coatings (TBCs) are used for increasing the efficiency and reducing pollutants of internal combustion engines (ICEs). In this paper, an optimization framework is developed in order to obtain the optimal dimensions for conventional coat, and the optimal dimensions and material property for functionally graded (FG) coat of a partially coated piston. A thermo mechanical analysis is investigated for Nano coat by finite element method. The conventional and Nano coats are made of MgZrO_3 as the insulating ceramic overlay and NiCrAl as the metallic bond-coat. The properties of the FG coat is assumed to vary according to power law through the thickness. For all tree conventional, FG... 

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... 

Type IV high pressure vessels are composite vessels with a polymeric liner, which are the best choice for storing hydrogen in hydrogen vehicles. The defect of these vessels is the penetration of light hydrogen molecules in the polymeric liner and the composite part. When depressurization the vessel, these molecules cannot release from the polymeric liner and the composite part according to the emptying rate of the vessel. Thus, concentration of the hydrogen molecules in the polymeric liner becomes more than inside the vessel which leads to a pressure difference between the two sides of the polymeric liner that causes the liner collapse. In this research, the partial differential equation for... 

Magnetic gels and ferrogels are smart composite materials made by combining magnetic particles in a polymer matrix. These materials have been considered due to their special properties such as deformation and change of mechanical properties in the presence of external magnetic field. Having polymer properties along with the magnetic properties of metals, have led these materials to many uses such as drug delivery and artificial muscles. The increasing use of these materials has led researchers to continue research in the field of modeling ferrogels. Due to the porous nature of ferrogels, the ability to absorb a lot of liquid and their large deformations in the magnetic field, modeling of... 

The concern of water shortage in the past years has caused special attention to advanced water purification technologies. Using solar steam generators to separate water from impurities has made us use both renewable solar energy and provide potable water. For solar radiation, the maximum steam production capacity is theoretically 0.7kg/(m^2 h), which is a small amount. To increase this capacity, advanced materials and structure design are needed to improve the heat capacity of the converter by reducing heat loss and better converting solar energy into heat energy. One of the advanced materials used to improve water purification efficiency is hydrogel containing metal nanoparticles. These... 

Microgels, three-dimensional networks belonging to the family of smart materials, exhibit significant structural changes in response to external stimuli such as temperature. The rapid deformation of microgels upon thermal stimulation makes them a promising alternative for various mechanisms. Despite the similarities between hydrogels and microgels, many of their properties differ. Moreover, the Flory-Rehner model, typically used to describe the swelling behavior of temperature-sensitive hydrogels, only provides a qualitative description of microgel swelling. Nevertheless, previous numerical models of microgels have largely been based on the assumption that their behavior mirrors that of... 

Classical theory of elasticity, which is founded upon results of mechanical experiments on the large scale materials, has reasonable results in predicting mechanical properties. The basic idea in this theory is that stress at a point of the material is only a function of the local strain and it is independent of the nonlocal strains. Therefore, the size of the material does not play any role in analyzing mechanical behavior of materials using this theory. However, results from experiments and atomic simulations have shown that in nano scale materials, such as carbon nanotubes (CNTs) and their composites, mechanical properties are strongly dependent on the size parameters of these materials.... 

Mechanical forces play a crucial role in tumor patho-physiology. Compression of cancer cells inhibits their proliferation rate and induces apoptosis. Additionally, compression of intratumor blood vessels has negative impacts on drug delivery system. Despite the great importance of the mechanical forces on the pathology of cancer, there are limited studies on the constitutive modeling of tumors. In this study, first, the tumor growth inside a rigid cylinder with an exponential growth function is represented, a model mimicking the growth of ductal carcinoma. Then, a mathematical model of a spherical tumor growth with a Gompertz growth function is represented. Using the notion of multiple... 

The improved properties of nanocomposites are not achievable with conventional composites. Scale effect is one the most important parameters in the physical and mechanical properties of polymeric nanocomposites. One of the physical phenomena, which can be related to the scale effect, is the very large interface between the nanoparticles and the polymeric matrices. Motional behavior and conformation of polymeric chains change near the nanoparticles surfaces. Due to high interface of the nanoparticles with the polymeric matrices the amount of these types of changes in the polymeric chains are so large that can change the physical and mechanical properties of polymeric nanocomposites. In this... 

In recent years, carbon nanotubes have been the focus of considerable researches. Numerous investigators have reported remarkable physical and mechanical properties for this new form of carbon. In particular, the exceptional mechanical properties of carbon nanotubes, combined with their low density, offer scope for the development of nanotube reinforced composite materials. The potential for nanocomposites reinforced with carbon tubes having extraordinary specific stiffness and strength represent tremendous opportunity for application in this century and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Classical theories of... 

Due to ignoring the effect of length scale and neglecting the details at nanosize, classical methods are not sufficiently accurate to determine the properties of nanostructured materials. More reliable results can be obtained, using surface elasticity theory. Lots of analytical, experimental and numerical investigations have been done on the effect of interphase on the mechanical properties of polymer nanocomposites whereas metal matrix nanocomposites are in the first stages of analytical and numerical researches and have attracted so much attention.
The main objective of this research is to investigate the effects of interphase as well as coating, on the mechanical behavior of metal... 

Strain rate dependence of plastic yield and failure properties displayed by most metals affects energies, forces and forming limits involved in high speed forming processes. This paper investigates the influence of the strain rate on the forming properties of some industrial sheet metals used in Automotive and Aerospace industries. First, Split Hopkinson Tensile Bar (SHTB) experiments are carried out to determine the influence of the strain rate on the materials’ stress-strain curves. Then, the SHTB results are used to model the constitutive behaviour of the metal sheets using the phenomenological Johnson-Cook (JC) and Voce models. Finally, forming limit diagrams (FLDs) are calculated using... 

Canard, first observed in Van der Pol oscillations, is a typical phenomenon in oscillatory systems. Canard is also observed in many oscillatory systems such as electrical circuits and neurons. In many fields of science and engineering there are complex oscillations that exhibit canard for certain values of parameters. These three dimensional systems exhibit complex oscillatory behavior never observed in two dimensional dynamics. Some of these systems are chaotic for certain parameter values. It seems than in oscillatory systems canards can make complex behavior. Several methods such as the singular perturbation theory have been used to study this complexity. In this project, we study canard... 

In the field of high-pressure material science, diverse carbon systems under pressure have been intensively studied with interest in synthesizing new phases. A variety of these synthetic phases which have met various applications in today technology are called the amorphous diamond. The pressure-induced structural transition of carbonaceous material to amorphous diamond is realized by shock compression and rapid quenching. The shock compression and rapid quenching generate the high pressure (several GPa) and the temperature (several hundred K) in a fraction of a microsecond.Since the mechanical and electrical properties of the synthetic diamond are severely sensitive to the atomic structure,... 

In novel drug delivery systems, once nanocarriers confront the biological milieu, their surface is rapidly covered with a layer of biomolecules (i.e., “protein corona”) which play an important role in their drug release rate. Various experimental studies have been done to elucidate the effect of nanoparticles properties on the drug release rate in different biological applications. The physical and geometrical properties of protein corona totally influence on the release profile. In this study, we proposed a suitable finite element model which contains the nanoparticles and the protein layer with their properties in the biological milieu. To this end, diffusion parameters including diffusion... 

Among the various materials, silicon anodes have the highest lithium absorption in lithium-ion batteries. But this high lithium absorption capacity can cause 300 percent volume expansion and large stresses. Experimental observations show that charge and discharge cycles may cause plastic deformation in some parts of the electrode particle. On the other hand, there is a possibility of a ratcheting phenomenon due to changing in elastic properties of the electrode material during the charging and discharging processes. However, this phenomenon has not been reported for silicon spherical electrode particles yet.This study aims to model the elastic-plastic behavior of silicon spherical electrode... 

Optical metasurfaces are 2D structures of a repetitive arrangement of a number of nanoparticles that are artificially constructed and do not exist in nature. Important applications of optical metasurfaces are meta lenses, flexible solar cells and extremely small antennas. Fabricating surfaces with nanoparticles of proper geometry under light radiation along with elastic deformation, we can have optical metasurfaces with selective reflection or transparency in the visible spectrum. The aim of this project is modeling of an optical metasurface with elastic deformation leading to change of color and transparency. For this purpose, assuming vertical light radiation and linear polarization, we... 

In most of the engineering applications, the mechanical behavior of materials in high strain rate deformations differs from their behavior in quasi-static deformations. In some engineering problems like impact loading on structures, metal forming and explosive forming, the range of strain rate is about . Taylor impact test is one of the experiments used for characterizing the dynamic behavior of materials in high strain rate deformations. In the Taylor impact test a rigid cylindrical projectile is impacted normally onto a hard and massive surface (anvil), the projectile deforms by mushrooming at the impact end. With plastic wave propagation analysis, the plastic deformation of projectile is... 

In this thesis, we aim to study the elastic-plastic behavior of short fiber reinforced composites experimentally and analytically. The experimental investigation is applied to glass fiber-polypropylene composites (PP/GF). The samples are produced by injection process with maximum temperature of 190C. Fibers are randomly oriented in this procedure of fabrication. The samples are tested in tension, and the mechanical strength is measured by changes in fiber content. The Young's modulus is also investigated in these experiments.Also in this thesis, an analytical model for calculation of Young’s modulus of fiber reinforced composite materials is proposed. In this analysis a displacement field is...