Sharif Digital Repository

Al-1100/St-12 aluminum clad steel sheets were produced using roll bonding process at different reductions in thickness and with various supplemental annealing treatments. Experiments were conducted by applying the Taguchi method to obtain optimum condition for maximizing the joint strength. The joint strengths of the bi-layer sheets were evaluated by peel test. The Al/Fe intermetallic phases at the joint interface and the peeled surfaces were examined using scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) and Vickers microhardness test were performed to characterize the intermetallic compounds. The results indicate that at the optimum condition of 0.50 reduction in... 

Microstructural development and phase formation at the interface of yttria stabilized zirconia (3Y-TZP)/430L stainless steel composite layers produced by co-sintering method were studied by SEM, HRTEM, micro-focus XRD, and EPMA. Formation of a rich chromium boundary layer at the interface was noticed, which revealed Cr aggregation at the interface at the elevated temperatures. Misfit dislocations were also observed at the joint interface to tackle the mismatch crystallographic orientations between the ceramic and metal layer. The results of the micro-focus XRD showed formation of no new phases at the boundary zone. Microstructural studies also revealed a retarded grain growth in the... 

The effect of surface and interface elasticity in the analysis of the Saint-Venant torsion problem of an eccentrically two-phase fcc circular nanorod is considered; description of the behavior of such a small structure via usual classical theories cease to hold. In this work, the problem is formulated in the context of the surface/interface elasticity. For a rigorous solution of the proposed problem, conformal mapping with a Laurent series expansion are employed together. The numerical results well illustrate that the torsional rigidity and stress distribution corresponding to such nanosized structural elements are significantly affected by the size. In order to employ surface and interface... 

We investigate heat transfer between parallel plates separated by liquid argon using two-dimensional molecular dynamics (MD) simulations incorporating with 6-12 Lennard-Jones potential between molecule pairs. In molecular dynamics simulation of nanoscale flows through nanochannels, it is customary to fix the wall molecules. However, this approach cannot suitably model the heat transfer between the fluid molecules and wall molecules. Alternatively, we use thermal walls constructed from the oscillating molecules, which are connected to their original positions using linear spring forces. This approach is much more effective than the one which uses a fixed lattice wall modeling to simulate the... 

In order to safe design and optimize performance of industrial systems which work under two phase flow conditions, it's often needed to categorize flow into different regimes. In present work the experiments of two phase flow were done in a large scale test facility with length of 6m and 5cm diameter. Four main flow regimes were observed in vertical air-water two phase flows at moderate superficial velocities of gas and water: Bubbly, Slug, Churn and Annular. Some image processing techniques were used to extract information from each picture. This information include number of bubbles or objects, area, perimeter, height and width of objects (second phase).Also a texture feature extraction... 

The effect of surface and interface elasticity in analysis of the Saint-Venant torsion problem of an eccentrically two-phase circular nanobar is considered. The problem is formulated in the context of Gurtin's surface elasticity. For a rigorous solution of the proposed problem, conformal mapping together with a Laurent series expansion are employed. At the nanoscales the usual classical theories cease to hold and the corresponding results deteriorate. The numerical results well illustrate that the torsional rigidity of the mentioned nanosized structural elements are significantly affected by the size. Some applications of the given results can be contemplated in the design of micro/nano... 

In the present work, the effect of brazing pa rameters on the properties of the brazed joint of pure titanium and 304 stainless steel (304SS) was investigated. Three different Ag-Cu filler metals were used, while the temperature and time of brazing were in the range of 800-950°C and 5-45 minutes, respectively. The microstructural observations show that, depending on the brazing conditions, different intermetallic phases such as CuTi2, CuTi, Cu3Ti4, and FeTi were formed at the phases interface. Based on the microstructural observations, a model was developed to characterize the formation of phases at the interfaces and brazed joint. The results show that, while some phases may form during the... 

The purpose of this paper is to investigate the effects of annealing phenomena on the energy absorption of Al-steel bilayer sheets, bonded by cold rolling, through wedge tearing. Tearing by wedge is a dissipating energy system that includes three components: cutting, friction and plastic deformation due to bending. In order to find the bonding and annealing effects on energy absorption, the non-bonded bilayer sheets are prepared in the same condition of bonded ones. The results show that energy absorption of bonded sheets is larger than that of non-bonded ones. This is due to different plastic bending moment of bonded and non-bonded bilayer sheets. Whenever the bond is improved by heat... 

Propagation of P-wave in an unbounded elastic polymer medium which contains a set of nested concentric spherical piezoelectric inhomogeneities is formulated. The polymer matrix is made of Epoxy and is isotropic; each phase of the inhomogeneity is made of a different piezoelectric material and is radially polarized and has spherical isotropy. Note that the individual phases are homogeneous, and all interfaces are perfectly bonded. The scattered displacement and electric potentials in the matrix are expressed in terms of spherical wave vector functions and Legendre functions, respectively. The transmitted displacement and electric potentials within each phase of the piezoelectric particle are... 

In this article, a multiscale modeling procedure is implemented to study the effect of interphase on the Young's modulus of CNT/polymer composites. For this purpose, a three-phase RVE is introduced which consists of three components, i.e., a carbon nanotube, an interphase layer, and an outer polymer matrix. The nanotube is modeled at the atomistic scale using molecular structural mechanics. Moreover, three-dimensional elements are employed to model the interphase layer and polymer matrix. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using this Molecular Structural Mechanics/Finite Element... 

Attempts were made to trace the effect of organoclay (OC) on the rheological and mechanical behaviors of the low density polyethylene (LDPE)/ethylene-vinyl acetate (EVA) blends. To do this effectively, in addition to LDPE/EVA/OC system, pure LDPE and LDPE/EVA blends were also examined as model systems. The rheological behavior was determined by the capillary rheometer. Morphological characterization was also carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and theoretical approach based on interfacial energies. Shear viscosity, tensile strength and elastic modulus of LDPE/EVA were found to decrease by increasing the EVA... 

The present study deals with the structure-property relationship of organoclay (OC) filled nanocomposites based on rubber blend comprising of nitrile-butadiene rubber (NBR) and phenolic resin (PH). To obtain a better insight into the characteristics of the NBR/PH/OC hybrid system, a simple model system consisting of NBR/OC nanocomposites is also taken into consideration. A series of NBR/OC and NBR/PH/OC nanocomposites containing a wide range of OC concentrations (2.5-30 phr) are prepared by using traditional open two-roll mill. Structural analysis performed by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) exhibits mixed exfoliated and... 

Effect of organoclay (OC) on the performance of styrene-butadiene rubber (SBR)/phenolic resin (PH) blend prepared by two-roll mill was investigated. The influence of OC content ranging between 2.5 and 30 phr on the performance of SBR/PH was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), interfacial energy analysis, tensile, dynamic mechanical, swelling, cure rheometry and thermogravimetric analysis (TGA). It was found that the OC is mainly localized in the SBR phase of SBR/PH blend through the kinetically favored mechanism relevant to rubber chains. The results also demonstrated the positive role of PH on the dispersion of OC. Both PH and OC showed... 

The mechanism of interface formation during sinter-joining of nanostructured yttria stabilized zirconia (27 nm) compacts with chromium powder was investigated. The effect of sintering atmosphere, i.e. argon or vacuum, was studied. Microstructural evaluation and phase formation was examined by scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), and micro-focused X-ray diffraction (MFXRD) methods. It is shown that spreading and evaporation-condensation mechanisms are responsible for the interface formation. An improved joint shear-strength was obtained after sintering in vacuum (74 MPa) compared with argon (41 MPa). The result of MFXRD indicated formation of Cr-island at... 

In order to relate the wetting properties at the pore scale to the macroscale prevailing forces, a series of experiments was performed in vertical porous media under forced gas invasion at various wettability conditions with partially spreading oil. To describe the dynamics of oil recovery in a three-phase flow condition, the downward gas flood experiments were continued by water injection from the bottom. Experimental results obtained in situations where the magnitudes of viscous, capillary, and gravity forces are comparable. We study the transition from flow configurations where the interface is stable with respect to viscous instability to flow configurations where viscous fingering... 

Stepwise-graded composite layer of M2 tool stel and 17-4PH stainless steel was fabricated by a simple powder layering technique and the isothermal and nonisothermal sintering response of the bilayer were examined. It was shown that the materials exhibit poor compatibility during co-sintering, i.e., the amount of mismatch shrinkage is significant. An improved compatibility was obtained by adding 0.2 wt% B to the stainless steel powder. Formation of relatively dense layer at the bonding zone indicated an enhanced densification rate at the interface. Microstructural studies showed formation of a ferritic interface in M2/17-4PH composite and elongated grains with an intergranular boride phase... 

Sintering response and phase formation during sintering of WC-Co/316L stainless steel composites produced by assembling of powder injection molding (PIM) parts were studied. It is shown that during cosintering a significant mismatch strain (>4 pct) is developed in the temperature range of 1080 °C to 1350 °C. This mismatch strain induces biaxial stresses at the interface, leading to interface delamination. Experimental results revealed that sintering at a heating rate of 20 K/min could be used to decrease the mismatch strain to <2 pct. Meanwhile, WC is decomposed at the contact area and the diffusion of C and Co into the iron lattice results in the formation of a liquid and MC and M6C... 

A comprehensive approach is proposed to manage landing sequences and their associated trajectories for an arbitrary number of aircraft in the vicinity of a controlled aerodrome. The current approach, similar to that of "first come, first served," could consider different types of priorities as well as emergencies. The approach is especially useful to combine unstructured free-flight trajectories with structured ones during the approach phase of the flight A comprehensive cost function considers the relative size of all aircraft together with their relative speeds and flight directions. This helps optimize the amount of fuel consumption while respecting separation minima. Resulting... 

In this work, we present a level set method to simulate steady and unsteady mass transfer from a single droplet moving in a second phase fluid under buoyant force. We initially use level set to determine the interface between the two phases, where the shape of drop forms. Next, we extend this method to solve a unique mass transfer equation for the entire solution domain without considering the discontinuity appeared at the interface. We use a finite element method incorporated with the characteristic-based split (CBS) algorithm to implement axi-symmetric mass transfer equations on a stationary Eulerian grid. Of course, the convection-diffusion modeling of mass transfer is different from the... 

Bead-chain-like ZnO nanoparticles (NPs) formed in colloidal solution from oriented attachment (OA) of spherical nanoparticles. Arc discharge in liquid is a cost-effective method for quick mass production of nanostructured materials without considerable environmental footprints. Applying voltage across two zinc rods as electrodes, which were immersed in water cause explosion of electrodes and plasma generation. Zn/ZnO nanocomposites produced by interaction of different active species in high-pressure and high-temperature plasma at the solid-liquid interface. Different sized nanoparticles with diameters of 26, 35, 40 and 60 nm at applied discharge currents of 150, 100, 50 and 20 A...