Sharif Digital Repository

In this study, a novel multi-scale hierarchical method has been employed to explore the role of edge dislocation on Nano-plates with hexagonal atomic structure in large deformation. multiscale hierarchical atomistic/molecular dynamics (MD) finite element (FE) coupling methods are proposed to demonstrate the impact of dislocation on mechanical properties of Magnesium in large deformation. The atomic nonlinear elastic parameters are attained via computing first-order derivation of stress with respect to strain of Representative Volume Element (RVE). To associate between atomistic and continuum level, the mechanical characteristics are captured in the atomistic scale and transferred to the... 

The most common method of oil recovery is by displacement. By injecting water into wells, to push the oil to production wells, ultimately, the injected fluid breaks through at the production wells. Estimation of breakthrough time is important for the reservoir engineering calculation and the prediction of enhance recovery scenarios. Oil reservoirs are extremely complex, containing geological heterogeneities on all length scales which have a significant impact on hydrocarbon recovery. The conventional approach to investigate the reservoir performance is to build a detailed geological model, upscale it, and finally run flow simulation which is computationally very expensive. In... 

Nowadays, robots are become more common in many important applications, such as academic and industrial issues. One of the most important robots are Multi-Arm manipulators which are used in many application such as moving objects, coloring, automatic welding and etc. Working with this kind of robots needs some vital attentions like planning their moving path. It is Because of the large number of obstacles that they face with in the path. Therefore, not only robots are not allowed to collision with themselves, but also they must not touch the obstacles. In the other words, they need Path planning. Generally, the equations of these robots are nonlinear. Therefore, computers and numerical... 

Multi-directional forging is used as a severe plastic deformation process for producing ultrafine grained materials in which a sample undergoes consecutive compressive strains and as a result, coarse grains break to smaller grains. The strength of multi-directionally forged material increases because of grain refinement, although the high strain energy reserved in a sample after large plastic deformation lessens its ductility. Metals experience non-isothermal heating cycle during annealing till they reach the target temperature. Non-isothermal heating cycle can affect microstructure and mechanical properties of severely deformed material due to its high strain energy. Thus, investigation of... 

In fractured reservoirs under the gravity mechanism, the oil transfer between the matrix blocks is affected by mechanisms such as capillary continuity or re-imbibition. Capillary continuity between adjacent matrix blocks can be created by formation of liquid bridges, or physical contact of surfaces due to the roughness of the fracture wall surface.Since the presence of liquid bridges can be effective in creating capillary continuity and therefore the amount of oil production, the study of the presence of liquid bridges between matrix blocks and how they change in terms of volume and shape in the process of oil and gas movement is of particular importance. Although there are studies on the... 

As petroleum resources are not steadily distributed in the world and all industries and manufacturing sections are dependent on these resources, petroleum transportation is very important to the extent that availability of these resources occurs in the fastest time and costing the least possible. The objective of this study is to study the petroleum distribution through time in the world and assess its transportation efficacy during 1965-2005 in 173 countries. Collecting information about petroleum distribution between exporting countries to importing ones helped to complete the study data base. Also in this study two transportation networks, sea and land multimodal transportation network... 

Several SPD methods have been invented for processing rods and sheets, and their physical and mechanical properties have been investigated so far. The materials processed by these methods have not been industrialized thoroughly. Moreover, in previous investigations, few works have been carried out on tubular types of materials. Thus, in this study, aluminum tube goes through a tubular channel in order to achieve different values of strains. This method is named Tube Channel Pressing. The mechanical and microstructural investigations on aluminum tubes which have been processed up to 5 passes shows that ultimate strength increases 1.7 times and sub-grains size reaches to 360 nm. Applying final... 

Wound healing by engineered scaffolds is a new step in bio-technology and medical studies in recent years. The goal of the current study is to propose a novel structure for a tissue-engineered scaffold to be used in wound healing. Influenced from the multi-layered structure of natural human skin, the fabricated scaffold consists of two layers to maximize similarity with natural skin. This product is comprised of an electrospun layer made of polycaprolactone and polyvinyl alcohol and a hydrogel layer made of chitosan and gelatin. In order to form a porous medium in the hydrogel layer, freeze-gelation was used instead of freeze drying. The evaluation of fabricated scaffolds was performed by... 

Polymeric microspheres which can load biomolecules, proteins and growth factors play an important role in tissue engineering and drug delivery systems. The size of the microspheres and encapsulation efficiency exert a considerable impact on the usability of them. In this study double emulsion method is used for fabrication of microspheres. Effect of different parameters namely the speed of homogenization, time of homogenization, the amount of polymer in oil phase, the surfactant concentration in different phases on the size and surface morphology of the microspheres are investigated. Moreover, a release test for BSA loaded microspheres is conducted. Results indicate that by increasing the... 

Corneal keratoconus is one of the common eye diseases that usually occurs in the teenage years or the beginning of the third decade of life. In this disease, the cornea thins and loses its original shape and becomes conical. To treat this disease, ophthalmologists use different methods such as using glasses, contact lenses (hard and soft), corneal transplantation, and also corneal cross-linking, each of these methods has limitations, on the other hand, considering that The disease progresses and its severity increases, Ophthalmologists use corneal rings to treat this disease in more advanced stages, implanting a suitable ring in the patient's cornea both increases the strength of the... 

In recent years, various research has been done on the severe deformation of low carbon steel sheets. One of the methods used is the pressing in the grooved die, only two passes of the pressing process in the grooved mold have been successful when applied to these sheets, but on the other hand, these two passes also lessen the sheet's ductility while increasing its strength. Due to the fact that the sheet surface produced by the pressing in the grooved die is not entirely smooth, the attempt in this project was to improve the ductility to some extent using warm rolling in addition to the smoothness of the surface using higher temperature while improving the strength or maintain it. To... 

One of the limitations of friction stir welding process is joining of sheets with low thickness. Interference ways for these limitations are joint in higher thicknesses and thickness reduction in included joint samples. In this study, in the first process, with the optimization of the variables affecting the process, joint was performed using visual inspection, mechanical properties and micro structural studies. In the next process, using the rolling operation for the reduction percent of different thicknesses, the most appropriate route was chosen. 1050 aluminum sheets (1050 and 6082-T6) with a thickness of 3 mm were welded using friction stir welding in tool rotary speeds of 1200 and 800... 

An increase in strength of friction stir welded (FSW) AA3003-H18 sheets is important, due to the reduction of mechanical properties in weld area such as heat affected zone and stir zone during welding. In this research, at first FSW was used to join 3003-H18 non-heat-treatable aluminum plates without adding copper powder. The specimens were joined at various rotational speeds (800, 1000 and 1200 rpm) and traverse speeds (40, 70 and 100 mm/min). In these cases, the effects of welding parameters on microstructure and mechanical properties were investigated. The average grain size of stir zone was in the range of 21.7-7.8 μm and the microhardness of them was 28-37 Hv. Then FSW was used to join... 

Friction stir welding (FSW) is an appropriate method for joining Aluminum structures. In this method lots of defects involved in other methods are not formed and good properties are achieved for Aluminum joints. The metal sheets joined by this method are used to manufacture metal structures bodies. One of the important issues in the structure bodies used in transportation is the amount of energy absorbed in collision with other objects. One of the methods to investigate the energy absorption is wedge tearing test and one other is tensile test. In the preset study two sheets of Al 1050 were joined using FSW method in different tool rotational and welding speeds. Firstly, the microstructure of... 

Carbon nanotubes are cylinders in Nano scale formed of carbon atoms with covalent bonds that contain a significant electrical and mechanical features. Carbon nanotubes are divided into two main types: multi-walled carbon nanotubes (MWCNTs) and single walled carbon nanotubes (SWCNTs). A SWCNT is a rolled graphene sheet (graphene is in fact a single sheet of graphite). SWCNTs has lately been considered as one of most interesting research cases. The reason why researchers have been fond of investigating about graphene has been its unconventional quantum hall effects, high room-temperature electrical conductivity and its mechanical stability despite of being composed of single layer atom... 

In this study, a novel multiscale hierarchical molecular dynamics (MD) – finite element (FE) coupling method is proposed to illustrate the influence of temperature on mechanical properties of heterogeneous nano-crystalline structures. The embedded-atom method (EAM) many-body interatomic potential is implemented to consider pairwise interactions between atoms in the metallic alloys with face-centered-cubic (FCC) lattice structure at different temperatures. In addition, the Nose-Hoover thermostat is employed to adjust the fluctuation of temperature. In order to calculate the equivalent lattice parameter, a weight average between the lattice parameters of atomic structures is utilized. The... 

In this study, a new multi-scale hierarchical technique has been employed to investigate the role of temperature on nano-plates with hex atomic structure. Different number of primary edge dislocations is considered and the temperature varies from 0 up to 800 K. Primary edge dislocations are created by proper adjustment of atomic positions to resemble discrete dislocations (DD’s) and then the application of equations of motion to the relaxed configuration of this adjustment. The interatomic potential used for atomistic simulation is Finnis-Sinclair Embedded-Atom-Method (FS-EAM) as many-body interatomic potential and the Nose-Hoover thermostat has been implemented to adjust the modulation of... 

In this study, two multiscale hierarchical atomisyic/molecular dynamics (MD)–finite element (FE) coupling methods are proposed to illustrate the influence of temperature on mechanical properties of SLGS in large deformation. The Tersoff interatomic potential is implemented, in addition, the Nose-Hoover thermostat and local harmonic approximation are employed to adjust the fluctuation of temperature in CB and MD, respectively. The atomic nonlinear elastic parameters are obtained via computing second-order derivative of Representative atom’s energy and RVE’s strain energy density with respect to deformation criterions (deformation gradient and Green strain tensor). To bridge between atomistic... 

In this study, a novel and unprecedented multi-scale hierarchical molecular dynamics (MD) – finite element (FE) coupling method is proposed to demonstrate the influence of temperature on mechanical properties of heterogeneous Nano-crystalline structures. The embedded-atom method (EAM) many-body interatomic potential is implemented to consider pairwise interactions between atoms in the metallic alloys with face-centered-cubic (FCC) lattice structure at different temperatures. In addition, the Nose-Hoover thermostat is employed to adjust the fluctuation of temperature. In order to calculate the equivalent lattice parameter, a weight average between the lattice parameters of atomic structures...