Sharif Digital Repository

In-situ aluminum matrix composites were fabricated by 1-3 passes of friction stir process (FSP) using iron (Fe) particles with initial size of 10. μm. Although the initial reinforcing particles were relatively large in size and also agglomerated particles were formed in the obtained composites, all of the processed specimens fractured from the base metal during transverse tensile test. Longitudinal tensile tests revealed that the ultimate tensile strength (UTS) of the composites was up to 43% higher than that of the base metal; however, the strain to fracture of the composites reached to about 0.2. Al-Fe intermetallic compounds (IMCs) formed at the interface of the aluminum matrix and Fe... 

Aluminum tubes were successfully fabricated using a novel process of friction stir back extrusion (FSBE) known as one of the severe plastic deformation (SPD) routes. It was found that this process is capable to form a tube with a significant fine grained structure resulting from dynamic recrystallization phenomenon in the stirred area. Several regions were identified in the formed tube in which various microstructural evolutions occur, i.e. dynamic recrystallized (RX), static RX, and partially static RX zones along with extruded base metal. There was also no considerable change in the hardness and strength values of the formed tube with respect to those of the extruded base metal. However,... 

The annealed 1050-aluminum sheets were initially subjected to the severe plastic deformation through two passes of constrained groove pressing (CGP) process. The obtained specimens were post-deformed by friction stir processing at room and cryogenic temperature cooling media. The microstructure evolutions during mentioned processes in terms of grain structure, misorientation distribution, and grain orientation spread (GOS) were characterized using electron backscattered diffraction. The annealed sample contained a large number of “recrystallized” grains and relatively large fraction (78%) of high-angle grain boundaries (HAGBs). When CGP process was applied on the annealed specimen, the... 

A one-dimensional kinetic Ising model at a finite temperature on a semi-infinite lattice with time varying boundary spins is considered. Exact expressions for the expectation values of the spin at each site are obtained, in terms of the time dependent boundary condition and the initial conditions. The solution consists of a transient part which is due to the initial conditions, and a part driven by the boundary. The latter is an evanescent wave when the boundary spin is oscillating harmonically. Low-and high-frequency limits are investigated in greater detail. The total magnetization of the lattice is also obtained. It is seen that for any arbitrary rapidly varying boundary conditions, this... 

In this paper, the mechanical properties of graphene oxide are obtained using the molecular dynamics analysis, including the ultimate stress, Young modulus, shear modulus and elastic constants, and the results are compared with those of pristine graphene. It is observed that the increase of oxide agents (–O) and (–OH) leads to the increase of C–C bond length at each hexagonal lattice and as a result, alter the mechanical properties of the graphene sheet. It is shown that the elasticity modulus and ultimate tensile strength of graphene oxides (–O) and (–OH) decrease significantly causing the failure behavior of graphene sheet changes from the brittle to ductile. The results of shear loading... 

The severely plastic deformed aluminum sheets were joined by friction stir welding (FSW). The technique used for imposing the severe strain to the sheets was constrained groove pressing (CGP) process. The specimens with three different imposed strains by CGP, which lead to different initial microstructures, were joined at various rotation (. ω) and traveling (. V) speeds. The microhardness measurements and microstructure investigations were carried out. It was revealed that after FSW process of the specimens strained by CGP process, grain growth and correspondingly hardness reduction were observed at the stir zone. Also, transverse tensile test was performed at all conditions. For the CGPed... 

In this work, 1050 aluminum (Al) sheets were annealed and severely deformed by 1, 2, and 3 passes of constrained groove pressing process to obtain the various initial stored strain values of 0, 1.16, 2.32, and 3.48, respectively. Friction stir processing (FSP) was then applied using SiC nanoparticles to fabricate Al/SiC nanocomposite with approximately 1.5 vol pct reinforced particles. Microstructural examinations revealed that an increase in the initial stored strain of the base metal led to the formation of finer grain structure after 1 pass of FSP. The finer grain structure occurred in the stir zone where a sufficient amount of nanoparticles with a relatively proper distribution existed.... 

In this research, 1050 aluminum sheets in the conditions of annealed and severely deformed by 2 passes of constrained groove pressing (CGP) process were used. Two passes of friction stir processing (FSP) were applied on the specimens. Also, another CGPed specimen was processed by 2 passes of FSP using SiC nanoparticles. The samples were then heat treated to study thermal stability of base metal, heat affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and stir zone (SZ). Microstructure examinations revealed that the annealed base metal was relatively stable upon heating even up to 400. °C and a little grain growth was evident. On the other hand, the CGPed base metal was fairly... 

In the context of controlled release drug delivery approaches, the systems providing zero-order release kinetics have special advantages. Through employing these systems, drug concentration could be maintained within the therapeutic window over release time; thus maximum effectiveness alongside minimized side effects of the drug are achieved. However, obtaining zero-order drug release is extremely challenging. One of the main obstacles is the fact that implemented devices should be designed to overcome the decreasing mass transfer driving force, especially, in polymeric systems in which diffusion mechanism is dominant. In this study, we developed a new configuration of a polymeric matrix... 

Cell lysis is the most important first step for molecular biology and diagnostic testing. Recently, microfluidic systems have attracted considerable attention due to advantages associated with automation, integration and miniaturization, especially in resource-limited settings. In this work, novel centrifugal microfluidic platforms with new configurations for chemical cell lysis are presented. The developed systems employ passive form of pneumatic and inertial forces for effective mixing of lysis reagents and cell samples as well as precise fluidic control. Characterizations of the developed Lab-on-a-Discs (LoaDs) have been conducted with dyed deionized (DI) waters and white blood cells... 

The 1050 aluminum sheets are severely deformed by two passes of the constrained groove pressing (CGP) process to obtain the strain of 2.32. Friction stir processing (FSP) is then performed on these specimens at two conditions of with and without SiC nanoparticles. Microhardness measurements indicate that in the state of FSP without any particle, the microhardness of stir zone is decreased due to the recrystallization and grain growth occurrence because of high stored strain energy in the CGPed specimens. In order to enhance the mechanical properties of the stir zone, SiC nanoparticles are used during FSP. Also, the effect of FSP pass number on the distribution of nanoparticles is... 

The microstructure evolutions of severely deformed aluminum sheets by Constrained Groove Pressing (CGP) after Friction Stir Welding (FSW) are investigated. To do so, the specimens are deformed in three different strains using CGP process which make different the initial microstructures. Then, the specimens are joined at various revolution pitches (traveling speed/rotation speed ratio) of 0.20, 0.25 and 0.33. mm/r. To understand the effect of initial strains on the properties of joints, the microhardness measurements and microstructure investigations of different areas from retreating to advancing sides of the joints are carried out. The results achieved from FSW of CGPed samples are compared... 

The severely deformed aluminum sheets with strain of 2.32 were successfully joined by friction stir welding (FSW) process. Welding was carried out at various rotation speeds of 600, 800, and 1000. rpm at traveling speed of 200. mm/min corresponding to various revolution pitches of 0.33, 0.25, and 0.20. mm/r, respectively. In order to investigate the thermal stability of the joints, annealing was carried out at temperature of 200 °C for 1. h. Microstructure examinations revealed that severely deformed samples were quite unstable upon FSW process. However, during annealing it was found that in contrast to regions of heat affected zone (HAZ) and thermo mechanical affected zone (TMAZ) where... 

In this work, friction stir soldering (FSS) as a new approach for fabrication of copper/copper lap joints was introduced. This process is principally based on the friction stir processing (FSP) that can be performed using FSP tools with and without pin on the top sheet. In the present study, Pb-Sn foil was used as a solder which would be melted and then extruded in the area between the copper sheets during FSS process. This process was carried out using tools with and without pin at various rotation speeds of 1200, 1400, and 1600 rpm and traverse speed of 32 mm/min. Also, the same joint was fabricated using furnace soldering to compare the mechanical properties obtained with FSS and furnace... 

It is known that discrete scale invariance leads to log-periodic corrections to scaling. We investigate the correlations of a system with discrete scale symmetry, discuss in detail possible extension of this symmetry such as translation and inversion, and find general forms for correlation functions. © 2003 Published by Elsevier Science B.V  

We consider a multi-species generalization of the Asymmetric Simple Exclusion Process on an open chain, in which particles hop with their characteristic hopping rates and fast particles can overtake slow ones. The number of species is arbitrary and the hopping rates can be selected from a discrete or continuous distribution. We determine exactly the phase structure of this model and show how the phase diagram of the 1-species ASEP is modified. Depending on the distribution of hopping rates, the system can exist in a three-phase regime or a two-phase regime. In the three-phase regime the phase structure is almost the same as in the one species case, that is, there are the low density, the... 

Severely deformed aluminum sheets were processed by friction stir processing (FSP) with SiC nanoparticles under different conditions to improve the mechanical properties of both the stir zone and the heat affected zone (HAZ). In the case of using a simple probe and the same rotational direction (RD) of the FSP tool between passes, at least three FSP passes were required to obtain the appropriate distribution of nanoparticles. However, after three FSP passes, fracture occurred outward from the stir zone during transverse tensile tests; thus, the strength of the specimen was significantly lower than that of the severely deformed base material because of the softening phenomenon in the HAZ. To... 

The texture development during friction stir processing (FSP) of 1050 aluminum severely deformed at the strain magnitude of 2.32 was comprehensively discussed. It was observed that the component B¯ of the ideal shear texture along with the cube texture was developed in the severely deformed base metal. The effects of base metal texture on the texture development of stir zone, thermo-mechanically affected zone, and heat-affected zone during FSP were examined. Also, the developed texture components in the vicinity of the FSP tool and the stir zone were correlated to the deformation induced by the rotating tool which consisted of pin and shoulder. The observed texture components in the... 

In this work, examinations on the microstructure and mechanical properties of plain carbon steel and AISI 430 ferritic stainless steel dissimilar welds are carried out. Welding is conducted in both autogenous and using ER309L austenitic filler rod conditions through gas tungsten arc welding process. The results indicate that fully-ferritic and duplex ferritic-martensitic microstructures are formed for autogenous and filler-added welds, respectively. Carbide precipitation and formation of martensite at ferrite grain boundaries (intergranular martensite) as well as grain growth occur in the heat affected zone (HAZ) of AISI 430 steel. It is found that weld heat input can strongly affect grain...