Sharif Digital Repository

Today, titanium and its alloys are the most widely used metals in manufacturing of biomedical implants. But unfortunately, most of bulk (nonporous) titanium alloys implants are facing problems such as stress shielding. If titanium is produced in such a way that has sufficient amount of porosity on the surface and inside of the sample, it provides sufficient space for connection and proliferation of new bone tissues and transmission of body fluids. However, machining of porous titanium causes pore closing. Due to the importance of recognizing the machining mechanism of materials such as porous titanium for manufacturing of implants, in this study micromachining of porous titanium with the... 

Nowadays, thin film alloy deposition has much importance. These alloys are used for various opto-electronic device applications such as liquid crystal displays, flat panel displays, plasma displays, solar cells and computer memories. Exact control of elements ratio in alloy is one of the important issues in deposition of thin film alloys. In alloy deposition with electron beam gun method from its elements, uniformity improvement of each layer is a way to maintain elements ratio in different parts of sample. This uniformity has much importance especially in optical coatings such as high quality antireflection coatings, highly selective filters and low loss reflectance coatings. In this... 

These days the usage of welded tailor blanks with sufficient stability and flexibility is accelerating rapidly in order to production of slighter parts and reduction of fuel consumption in transportation means. Therefore, the conjuncture of blanks by welding methods is highly considerable before forming and ultimate production. Friction Stir Welding is greatly appealing to industry as one of the newest methods of solid state welding in production of TWB blanks. In this research, the feasibility study of Friction Stir Welding of thin Al 1100 – H18 alloy blanks with 1.5, 2 and 2.5mm thickness has been evaluated first. After creation of sound welds with same thicknesses, Friction Stir Welding... 

Deriving the shape, area, volume, and orientation of a defect from the ultrasonic nondestructive testing images of the oil pipelines, paves the way for the estimation of its severity. This paper describes the design and implementation of an automatic structure which can move an ultrasonic probe over the surface of a test sample, while preserving the distance, i.e. stand-off, between them, whatever the shape of the surface might be. The fixed stand-off is implemented, closing a feedback loop with a distance meter sensor. Also an integrated software environment is developed for the control of the table, data acquisition, data processing and displaying the results. After acquiring the... 

In this study the axisymmetric and asymmetric problem of interaction between a transversely isotropic half-space and various rst order shear deformation plate theories including Mindlin, Reissner and Vasil'ev are addressed. In order to improve the accuracy of solution, the surface boundary conditions of the half-space are modied.Moreover, the results compared with the exact solution and the most appropriate result is identied. The displacement Green's functions are obtained for both cases, modied and unmodied boundary conditions which can be expressed in a closed form and a numerically evaluated part. The latter is calculated exploiting Built-in numerical interrelation function of... 

Stress Absorbing Membrane Interlayer (SAMI) is a slightly thin layer made of bitumen and aggregate placed between a pavement with limited cracking and overlay in order to avoid reflective cracking in overlay. SAMI’s performance depends on many factors such as pavement layer’s materials and thickness and existing pavement’s condition. Numerical simulations are powerful tools to evaluate SAMI’s performance. Previous studies showed that construction of SAMI does not necessarily reduce reflective cracking. This research investigated the effect of different parameters on SAMI’s performance using numerical simulations. The focus of this study was on the performance of SAMIs used between asphalt... 

In the present study, the buckling of generally laminated truncated conical shells having thickness variation expressed by a linear function, subjected to axial compression with simply or clamped supports has been considered. To begin with, the fundamental relations for a conical shell with variable thickness have been derived applying thin-walled shallow shell theory of Donnell-type and theorem of minimum potential energy; non-linear terms of Donnell equations by the help of adjacent-equilibrium criterion are linearized. Governing equations are solved using power series method and are applicable for all combinations of classical boundary conditions. The results are validated with Galerkin... 

The need to build underground structures like tunnels, oil reservoirs are increasing and it requires a good knowledge of behavior of mass rock, exact data and parameters for safe and economic design. Filling materials which usually transfer with water into the joints reduce shear strength of joints significantly and change the behavior of the joints. To evaluate shear behavior of filled joints, 24 tests were conducted with large scale direct shear test apparatus on model rock joints with a regular “saw tooth” surface profile with the dimensions of 15cmx15cmx18cm. Filled material had specified specifications like particles size and strength parameters.
Infill thickness, moisture content... 

Casting process with foam is a relatively new process which because of having multiple benefits (like elimination of muscle and segregation line, high dimensional precision and using sand without using glue) in recent years has been considered. Considering that during pouring, melt replaces with sand surrounded foam, successfulness of this method depends on complete elimination of foam model during Pouring for preventing formation of some defects like carbon defects in cast irons, or cold work and porosity in aluminum alloys. Parameters like Pouring temperature, alloy type, foam type, density of foam model, type of gating system, and some other parameters are affecting the way of filling of... 

Commercially pure titanium (CP-Ti) is an important groups of titanium family and because of high strength, low density, high corrosion resistance and biocompatibility, this group of titanium is a suitable choice for application at chemical, petrochemical and medicine industry. Nowadays surgeons have a tendency toward use of CP-Ti instead of Ti-6Al-4V alloy. Moreover, because of body anatomy limitation, use of thick sheets result in high volume and damage soft tissue. Therefore, for sheet thickness reduction, study of the effects of metallurgical and geometrical parameter on fracture behavior of thin sheets is important. In this study, the fracture behavior of CP-Ti thin sheets investigated.... 

Mode І critical strain energy release rate at crack initiation, Jci, of SAC305 solder joints between two copper substrates was measured using double cantilever beam (DCB) specimens at a strain rate of 0.03 s-1 as a function of bond-line width (i.e. joint size in the out-of-plane dimension), solder thickness, copper adherends thickness and suface roughness. Fracture force per unit width and Jci were relatively insensitive to width of the joint ranging from 8 to 21 mm. Variations in solder thickness (i.e. 150 µm, 250 µm and 450 µm) also had an insignificant influence on the fracture energy of solder joints. This behavior was explained in terms of stress distribution, plastic zone area and... 

Dynamic impedance functions method is most recent approach in the analysis of soil-foundation dynamic interaction, and presented for massless rigid foundations. Impedance functions are frequency dependent functions, and used to obtain dynamic response of foundation with arbitrary mass subjected to dynamic loading of any frequency and magnitude. The important assumptions for appropriate useof mentioned method are rigidity of foundation and visco-elastic behavior of the soil beneath the foundation. In this study, experimental vertical impedance functions of square and circular foundations have been investigated,using physical modeling tests. A granular soil layer with finite thickness... 

Nowadays functionally graded materials have many applications in various industries. One of these applications can be the manufacturing of thick-walled vessels. Thick-walled vessels under internal pressure and high temperatures gradient require materials with higher strength, like Functionally Graded Materials (FGM) and can be reinforced by some mechanical processes like autofrettage. In this process under certain loading some part of vessels enters into plastic zone and upon unloading some residual stresses will be generated. Moreover it is very important to find out the depth of this plastic zone, In addition, minimizing the stress distribution vs. depth of plastic zone under applied... 

The present work has been planned to elaborately investigate the key parameters which affect the formation of shrinkage porosities during centrifugal casting of ductile cast iron pipes. The porosity defects can be mostly found in the Hot Mould centrifugal casting products and adversely affect the final mechanical properties of ductile iron pipes namely Ultimate Tensile Strength and Elongation.
In the first point of view, the created defects were detected through microstructural observations and the corresponding responsible mechanisms were also discussed. The results showed that the inner porosity is produced because solidification occurs from both the inner and outer surfaces... 

In Fourier domain optical coherence tomography, we can measure the optical thickness (refractive index n times thickness d), of sample’s layers. In this work, we introduce a new method for measurement of refractive index and physical thickness of multiple layers simultaneously by Fourier domain optical coherence tomography, without additional information about the structure of the sample under investigation. The input data to the formulation are the optical path lengths (OPLs) and suitable set of wavenumber of the FD-OCT interference spectrum. The output of simulation suggest that, the accuracy of the extracted parameters depend on the difference in the refractive index gradient of sample... 

With the progress of engineering science, the development of underground spaces and buried tunnels has witnessed remarkable expansion. Considering the frequency of hazardous events such as earthquakes and unforeseen consequences arising from underground activities and geology in underground engineering, the determination of the Dynamic Stress Concentration Factor (DSCF) has been widely recognized as a crucial factor in the study and design of tunnels and underground structures. It is also extensively considered in evaluating their damage. The investigation of wave dispersion and determination of the stress concentration factor was first proposed by Sezawa (1927). In this study, the... 

A semi-analytical solution for rotating axisymmetric disks made of functionally graded materials was previously proposed by Hosseini Kordkheili and Naghdabadi [10]. In the present work the solution is employed to study thermoelastic creep behavior of the functionally graded rotating disks with variable thickness in to the time domain. The rate type governing differential equations for the considered structure are derived and analytically solved in terms of rate of stress and strain as a reduced to a set of linear algebraic equations. The advantage of this method is to avoid simplifications and restrictions which are normally associated with other creep solution techniques in the literature.... 

High-strength low alloy (HSLA) E275 developed specifically for automotive application. Also St12 Steel is used in autobodies. On the other hand the resistance spot weld of dissimilar materials is generally more challenging than that of similar materials due to differences in the physical, chemical and mechanical properties of the base metals. The influence of the primary welding parameters affecting the heat input such as; current and time on the morphology, fracture mode, microhardness, and tensile shear load bearing capacity of dissimilar welds between HSLA E275 steel and St12 steel in two different thicknesses (1,2 mm) has been investigated in this study which consisted six group. The... 

Using thick plates is common in different industries including ship and pressure vessel manufacturing.In this research a plate forming method called line heating is examined. This method requires basic equipment and is very economical.Heat transfer between gas torch and plate is studied in more detail. Impingement jet model is used to simulate the effect of torch on plate. Velocity and temperature fields of exiting air are calculated in Fluent, a commercial software. Then heat is transferred between hot air and plate, which is related to velocity field and both temperature distribution of air and plate. In this method torch moves along the plate. In order to simulate this movement, a moving... 

Development of composite materials is one of the boldest technological advances of the last half of the twentieth century. This is due to their specific characteristics mostly considerably high strength-to-weight ratio, compared to metals and their highly customizing properties for different applications which make them a suitable material to be used in variety of domain from aerospace and automobiles to medical and sport equipments. Multi-stable asymmetrical laminates and non-uniform thickness laminated composite beams are being used as structural elements in a wide range of advanced engineering applications. Multi-stable asymmetrical laminates can be snapped between two or more geometries...