Sharif Digital Repository

In this thesis the tow-dimensional wave propagation in a functionally graded elastic medium is considered. It is assumed that the stiffness and density of the medium vary continuously in one direction. This work presents analysis in both time and frequency domain. In time domain, a graded element is presented for static and dynamic analyses in FGMs. This element clearly simulates wave propagation in inhomogeneous materials. The most important property which an element must have to be reasonable in wave propagation analyses in FGMs is simulating reflection only from boundaries. In frequency domain a dynamic stiffness matrix is generated using stiffness and mass matrix used in time domain... 

Here, we have simulated isothermal vacuum assisted resin transfer moulding (VARTM) using a control volume/finite element scheme. Two dimensional and dimensional (shell geometries) spatial discretization is used. Resin motion through fibers is enforced by vacuum negative pressure in downstream. The governing equations are mass conservation and well known Darcy equation. Using an unstructured triangular grid, complex geometries could be modelled. Application of a quasi-steady algorithm results in a system of linear equation for pressure distribution. This system must be solved in each time step. The point successive over-relaxation (PSOR) scheme is used to solve the system of linear... 

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,... 

In the present study the hot deformation behavior and the effect of hor rolling variables on the shape memory properties of a Ni-Ti shape memory alloy was studied. In order to simulate the hot compression test Abaqus softeware was employd. The results proved the pronounced increase in the specimen temperature at high strain rates and low temperatures (47 °C at strain rate of 1 s-1 and temperature of 700 °C). Thus, the effect temperature rise due to deformation heating on the characterisitics of the flow curves was eliminated. Afterwards, the corrected constitutive equation of the alloy was obtained and the rolling plan was designed. Shape memory measurments showed that two-way shape memory... 

Members of Centaurea species are common traditional medicines throughout the world. For this reason medicinal plants are the targets of intense Phytochemical studies. In this research we have investigated Centautea Golestanica which are members of this genus and endemic of Iran. In this research, One Flavonoid, two Sesquiterpenelactones and two triterpenoides were elucidated by advanced spectroscopic techniques such as IR, MS, 1H NMR, 13C NMR and 2D NMR. In continuation of this research, we have reported new and efficient methods for the synthesis of hitherto unknown indole-annulated pentacyclic indolylhydroisoquino lines and naphthooxazocines via tandem dinucleophilic addition of... 

Nowadays, autonomous underwater vehicles (AUVs) are implemented to carry out various activities under water. Amongst applications of these vehicles we can mention monitoring of marine creatures, mine installation and neutralization, and many military applications. The objective of this research is designing a control algorithm for underwater vehicles such that an under actuated vehicle can reckon a moving target as a reference and whilst chasing it, vehicle can keep a fixed distance from this target. First the dynamics of underwater vehicles are modeled and in this modeling different effects due to under water motion such as drag force, buoyancy force, and also added mass are included... 

The numerical modeling of engineering contact problems is one of the most difficult and demanding tasks in computational mechanics. Frictional contact can be observed in many problems; such as: crack propagation, metal forming operation, drilling pile etc. In metal forming operations the required shape changes are obtained by either of forming process, such as pressing, hammering, rolling or extruding the material between the tools which are much stiffer than shaped material. Because of large difference between deformability of the tool and material, relative movements occur in contact area. These relative movements produce the normal and tangential stresses, which have important role on... 

More than 70% of the components used in aerospace, aircraft and defence industries Are made of aluminum alloys. The 7xxx series of Al alloys such as AA7075 and AA7175 are typical alloys utilized in the mentioned industries. For these alloys, the optimization of the extrusion process in term of reaching a maximum extrusion quality without jeoparding the extrudate, the surface and microstructural properties is far more complex than other aluminum alloys. It is generally accepted that product properties are closely correlated to microstructure. So it is of paramount importance to understand the way in which the structure is modified and how the forming parameters i.e. temperature, ram speed,... 

Taking advantage of aluminum and its alloys in industry is increasing. A common method in metal forming is hot forming. In this condition a precise prediction of flow behaviour of the alloy is necessary to achieve a product of desirable mechanical and physical properties. In this situation, influence of parameters such as chemical composition, temperature, strain, strain rate as well as recovery and recrystallization phenomena should be considered and by using a suitable model, the metal behavior prediction is possible. Distribution of coherent Al3Sc dispersoids in high volume fraction accompany with Al6Mn result in strengthening to this alloy. Because of the high stacking fault energy,... 

The manufacture of ultra high strength materials has always been a target for aerospace and transportation industries. Currently, the limitation of energy resources even makes this goal more serious. Nowadays, more than 50% of total extrusion products are made from Al alloys and around 90% of them are the 6000 series alloys. Therefore, regarding to high strength, low weight, and hardening aluminum AA6000 alloys capabilities can play a major role in fulfilling this task. Over the last decade, a number of techniques collectively referred to as severe plastic deformation (SPD), have emerged as a promising approach for the production of bulk ultrafine-grained (UFG) nano-structured materials.... 

In recent years, more attention was devoted to ECAE process than any other Severe Plastic Deformation (SPD) process. Repeatability of the process and high mechanical properties of the exit profile are the reasons of this attention. ECAE process carried out with conventional extrusion process, provides more strain and back pressure. In this thesis an analytical model based on upper Bound analysis and Bezier interpolation functions is presented and the effects of process parameters were studied. According to the presented model, reduction of inner corner angle φ, increases strain, strain rate and press force. Reduction of the outer corner angle ψ, causes the same effect. Moreover, decreasing... 

A new method for production of bimetallic rods, utilizing the equal channel angular extrusion (ECAE) process has been introduced before by previous researchers, but no attempt has been made to assess the effect of different temperatures and holding times in order to achieve a diffusional bond between the mating surfaces. In present research copper sheathed aluminum rods have been ECAEed at room temperature and subsequently held at a constant ECAE pressure, at different temperatures and holding times to produce a diffusional bond between the copper sheath and the aluminum core. The bonding quality of the joints was examined by shear strength test. The microstructure examinations were carried... 

The main popuse of this Thesis is investigating of the different wagon arrangement effect on stability of the train set. So to gain this goal, one train with 10 wagons has been simulated. The model of the each wagon is Nonlinear with 40 DOF. 3 of the wagons are heavy and make 3 different kinds of arrangement by putting them at first, middle and the end of the train (HLL, LHL and LLH arrangements). Then these three arrangements have been simulated on two differen tracks and conditions, 1st Accelerating on curved track (320 R) with positive slope and 2nd decelerating on curved track with negative slope.We suppose that the contact is singular point and aslso contact equations have bben solved... 

In this investigation, effects of static restoration phenomena on microstructure and mechanical properties of A286 superalloy were studied. Therefore, single hit and double hit hot compression and hot rolling with different delay time at temperatures of 1050 and 1100 °C in strain rate of 0.1 and 6 s-1 were applied. In addition, annealing of cold compressed and cold rolled samples with various amounts of strains in temperature range of 1000-1100 °C were performed. Finally the best method for forming of A286 superalloy was proposed.Single hit hot compression test results shows that dynamic recovery and dynamic recrystallization occurred at temperatures of 1050 and 1100 °C respectively.... 

In this thesis we consider the effect of random locations of users in the capacity analysis of SIR-based power control systems and comparison to the strength-based systems, for the first time. Unlike previous works we do not consider a simple deterministic uniform model for the analysis. We provide simulations and analytical solutions for calculating the interference statistics, based on which, we not only calculate the interference statistics, but also study the effect of locating a user in every location in the network coverage area and its share in the interference. We also calculate each cell’s share in every statistics of the interference. In this thesis, based on the common assumption... 

Wall-Frame interaction under lateral load has been considered in studies, and it is concluded that interaction lateral forces of rigid frame and shear wall varies at different stories. This is resulted from of different mode shape of rigid frame and shear wall under lateral loads which are shear and bending mode, respectively. However most codes recommend a minimum strength for frame, equal to 25% of total lateral force, as an acceptance criterion of shear wall-frame dual action; otherwise this minimum strength does not fully comply with horizontal distribution of lateral load according to relative stiffness of components.The purpose of this article is to study nonlinear seismic response of... 

The A-286 superalloy is an iron-nickel base alloy having properties such as oxidation resistance and high mechanical strength. In addition, good producibility and high workability are the important properties of this alloy. In the present work dynamic restoration mechanism of A-286 supper alloy during thermo-mechanical processing has been studied. The aim is to verify the dominant restoration mechanism in different deformation conditions and also to determine the desire deformation parameters for hot rolling. In this regard, utilizing compression test in the range of 950 to 1100ºC and strain rate of 0.001 to 1 per second, the strain-stress curve for this alloy was obtained. After correction... 

The most important desire of all researchers in food industry is decreasing the contamination of foods and increasing their shelf life. Due to harmfulness of chemical preservatives their use has been limited and therefore natural antimicrobials have been demanded. Recently spices have been noticed as natural antimicrobial agents. Sumac is a kind of spice which has antibacterial and antioxidant activities.The aim of this project is to investigate effects of water and alcoholic extracts of Iranian red sumac comparatively on three gram positive bacteria (Bacillus coagulans , Bacillus subtilis, Staphylococcus aureus) and one gram negative (Escherichia coli) by well and disk diffusion method.... 

Various forms of springs are applicable, among which spiral and leaf springs can be named. Definition of leaf springs is conventionally applied to constant-width springs and is consisted of step-like leaves, each leaf having constant width. Leaf springs are largely used in vehicles, where they act as a part of suspension system supporting the weight of the vehicle along with connecting spots axles to the chassis. Springs so installed are capable of handling starting and stopping torques as well as sudden vibrations due to load carrying. Most Conventional method of manufacturing leaf springs is to bend strips of appropriate steel between curved dies, quench the strip while held between the... 

Memory organization plays an important role in embedded systems. Among the various component, memories as principle of consumption large amount of energy, are more important in power consumption, real time feature and fault tolerant of system.so that depend on system application, various configuration of memory organization are used…………. Memory organization issues include memory size, memory management methods, hardware management unit, cache, SPM and theirs subject and so on. This thesis discussed important topics related to energy consumption, real time and fault tolerant feature in memory organization and purposed a Configurable Description of Memory Organization for Low-Energy and...