Sharif Digital Repository

Emission of the greenhouse gases is a great concern and use of lightweight materials in transport vehicles has found a major importance in this respect. Metal/polymer laminated composites are of great interest due to their special mechanical properties and thoughness. Application of metal/polymer sheets is limited because of low bonding strength of metals and polymers in these sheets, which is not sufficient, to endure the stresses and strains during deformation processes such as deep drawing and bending. In this research, roll bonding of AA5052/Polypropylene sheets is investigated and the effects of bonding parameters on strength are evaluated and finally the bonding mechanisms during... 

Since the discovery of nanomaterials, the nanotubes have found special considerations. The high strength beside the low density, have attracted the interest of the scientists and engineers. Nowadays, one of the common methods to produce composites with high specific strength is to utilize of the nanotubes in the matrix of lightweight metals and alloys such as magnesium and aluminum. Recent researches indicate that very limited focus has been given to the production and properties of the magnesium - carbon nanotube composites and their workability. In this research, magnesium alloy - carbon nanotube composite is produced by casting method and its strength and workability are investigated as... 

Having the high strength to weight ratio has been made the composites special materials very important these days. The low density of aluminum and its appropriate corrosion properties make it a good choice for metallic matrix. Also, the high tensile strength of stainless steel fibers can helps as a reinforcement in the composite to improve its mechanical properties. Enhancing the bonding of composite’s components can helps it to develop its properties. Casting is an appropriate process for making an aluminum matrix containing steel fibers as reinforcement in a structural composite. In addition, rolling process can remove so many defects made by casting, and improve joining of fibers and... 

Cardiovascular disease is responsible for a majority of health problem in developing countries. Heart diseases are the leading cause of death in the United State with approximately 40% of the death occurs by heart failures and coronary artery defects. Myocardial infarction is one of the diseases that occurs by coronay artery blockage. Cardiac tissue engineering (CTE) is an emerging field that holds great promise towards the development of innovative treatment strategies for heart disease. There are two common scaffolds for CTE, electrospun fiber mats and hydrogels. Although fibers are known as 3D environment for cells, they actually act as a 2D surface, because of lack of cell infilteration.... 

Double network (DN) hydrogels are a new interpenetrate polymer network (IPN) that are usually contain about 60-90 % water. Despite of this amount of water, they are though and strong. DN hydrogels comprise of two networks, the first one as the brittle gel, is generally high density crosslinked and the second one, the loose and stretchable network, is loosely crosslinked or even without crosslinking. Therefore, we used cationic polymer, chitosan, and anionic polymer, alginate, as the first networks, therefore, we used sodium phosphate for physical crosslinking of chitosan, and calcium chloride as the physical crosslinking agents for alginate network. Also, poly (vinyl alcohol) (PVA), as the... 

Polymer composites, due to its exclusive properties, has a special place in industry. Epoxy resin with high adhesion property, low density, thermal stability and high chemical resistance has a special place as matrix in fabrication of high technology hybrid composites. Hybrid composites, due to its high strength and long fatigue life, used to reinforcing building structures and manufacturing fuselage. Layer and reactive structure near the firm core and wear-resistant of NDs, used to improvement of epoxy reisn and hybrid NanoComposite interphase properties. In this study, for improvement of the properties of hybrid NanoComposites, used the NDs in 0.25, 0.5 and 1 %wt with amine and carboxyl... 

Nanodiamond (ND)/polylactic acid (PLA) nanocomposites have the potential for biomedical applications and bone tissue engineering. In this research, nanodiamond/poly lactic acid nanocomposites were prepared by mechanical mixing solution method and applying ultrasonication. Also, PLA-based nanofiber scaffold reinforced by nanodiamond were prepared by electrospinning methods. To find the optimum value of parameters to prepare this nanocomposite sample, the effect of nanofiller concentration, mixing rate and duration, the role of solute and ultrasonication, and solvent evaporation conditions were investigated and then it compared to the neat polylactic acid sample. By means of Fourier transform... 

The aim of the present study is to investigate the effects of using hybrid fibers on rheological, mechanical and durability properties of the high-strength Self-Consolidating Concrete (SCC). For this purpose, two types of fibers including hooked-end steel fibers and polypropylene fibers were used. In this study, a total of eleven mixtures were used: one as a control mix, one containing 0.5% steel fibers, four containing 0.5% hybrid fibers (steel and polypropylene), one containing 1.0% steel fibers and the four containing 1.0% hybrid fibers (steel and polypropylene). For investigating the rheological properties, slump flow, J-ring and V-funnel tests were performed. Mechanical properties were... 

In this research, low carbon steel rolled under 16%, 33% and 50% deformation and applied under electric pulses. Microstructure investigated by optical microscopy and scanning electron microscopy in order to observe grain size, precipitation size and distribution and hardness measured by Vicker's hardness test, after each electric pulse treatment. I order to investigate microstructure evolution as well as grain size, precipitates and hardness all the species with different deformation percentages applied under electric pulses with different total electric pulse duration, number of pulses and the off time between two successive pulses. To obtain required information about species with... 

Methods that has been used for articular defects are faced with many limitations, so new therapies based on tissue engineering were taken into consideration in recent years. However, tissue engineering also encounters challenges regarding optimal scaffold construction and suitable cell source selection. Mature harvested chondrocytes are limited in number and may lose their chondrogenic potential in several cultures, leading to dedifferentiation. In addition, using stem cells also presents unique challenges associated with them, among which hypertrophic differentiation is the most substantial problem. Choosing the appropriate biomaterial similar to the cartilage structure with sufficient... 

Nowadays, modeling the behavior of materials during forming processes is so important. The role of most of them is to investigate and predict the evolutions of microstructure and mechanical properties of materials during plastic deformation. Previous researches have demonstrated that the best parameter to investigate these evolutions is the dislocation density of materials. In this study, first, the dislocation-based models, which investigate the material parameters evolutions during plastic deformation, were investigated and it was revealed that among all presented models, only the two internal variables models can investigate the behavior of materials during severe plastic deformation. ... 

Al-Mg alloys are used in many industrial fields, thus improvement of their mechanical properties is so important. Expressing mathematical models on the basis of physical and microstructural properties can be useful for this purpose. In this research, in order to study the microstructural evolutions and mechanical properties of the material, a dislocation based model and microstructural parameters such as grains and subgrains during plastic deformation and subsequent annealing are considered. In addition, a modification is used to make the model capable of justify the solute atom and temperature effect simultaneously. This makes the results to be more precise and accurate considering... 

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... 

FGM sheets with component or grain size gradient in their thickness direction provide mechanical and physical gradient properties through ND direction. FGMs are fabricated by various methods including centrifugal casting, powder metallurgy, PVD and CVD,all of which suffer from some shortcomings such as porosity of the products, low rate and high cost of production and restrictions on mass production. In this study, 2 and 4 layered Al matrix FGM sheets containing SiC and Al2O3 powders were fabricated by laminating method of Accumulative Roll Bonding(ARB). Two approaches of stacking were chosen as accumulative coupled roll bonding (ACRB) and (ASRB) for initial roll bonding and subsequent... 

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 this study, Butt resistance welding of copper to aluminum wires was studied. In this regard, the effect of current, pressure, post weld heat treatment and using intermediate layer of tin on the microstructure, strength and special electrical resistance of welds were examined. Based on a series of initial tests to establish the connection with the appropriate strength, the diameter of the aluminum and copper wires respectively 3 and 3.5 mm and their length 9 and 3.5 cm were selected. In order to weld samples, currents 4.4 to 4.7 KA and pressures 0.3 and 0.5 MPa were used. Then post weld heat treatment at currents 0.5, 1 and 1.5 KA on the welded sample in the pressure 0.3 MPa and the... 

Fe-29Ni-17Co alloy with commercial name “Kovar” is an alloy with low expansion coefficient. The main specification of this alloy is to maintain this property at the high temperatures that is used in sealing of glass-metal. Achieving to desirable physical properties associated with suitable mechanical properties is the purpose of related industries. However the effect of cold work and heat treatment was studied on the physical properties of this alloy, there is no report about the effect of the hot work. Thus, in this investigation, the effect of the hot work on the physical and mechanical properties of Kovar was studied. At first, slabs of Kovar alloy were cast and remelted. Then,... 

The unique properties of graphene due to the presence of massless Dirac fermions, high surface to volume ratio, high crystal quality in 2D, and high mechanical strength, recommend it as a promising material for technologies such as nanoelectromechanical systems (NEMS) and nanosensors. Use of graphene in nanodevices is accompanied by induced strains and stresses. Therefore it is important to study the mechanical properties of graphene. In present thesis, we synthesized graphene using both mechanical cleavage of graphite and chemical method. In the chemical method graphene oxide is prepared by oxidation and exfoliation of graphite. The graphene oxide sheets were reduced to prepare graphene... 

In the present study, the microstructural and textural evolutions and mechanical properties of 1050 Aluminum alloy was investigated through ECAP processing. The effects of annealing and strain path change by cold rolling on the ECAPed specimens were also investigated. The number of ECAP passes, annealing temperature and reduction of area during cold rolling were chosen as the variable parameters. The results showed that the grains became finer by increasing the ECAP passes. It is shown that the volume fraction of low angle grain boundaries increased in the first two passes. However, the volume fraction of high angle grain boundaries increased in the next passes. Continuous dynamic... 

Metallic multilayer composites provide remarkable mechanical, electrical and magnetic properties. These kinds of composites have been recently processed by severe plastic deformation (SPD) methods. Accumulative roll bonding (ARB) is one of the SPD processes in which accumulation of strain by repeating cycles, leads to the ultra fine grained materials. The goal of this research is manufacturing of Al/Ni composite sheets by ARB process considering the effects of thickness and number of initial sheets on their mechanical properties and microstructures. The initial composites were produced by commercially pure Al and Ni as the matrix and the reinforcement, respectively. Thickness of the Al...