Sharif Digital Repository

The delamination phenomenon has been studied in macroscopic scale by different approaches. Here, using micro-mechanical models, it is tried to find the possible relationship between the problem and the stress fields around a fiber. Using the ideas and the results on the free surface cracking of unidirectional composite, the FEM model is developed. The model verification is done by comparing the results by the results obtained in presence of damaged incorporated by the damage theory. Here, on the free surfaces fiber/matrix debonding is applied as a composite damage and the results show a good agreement with the available results  

Pure Zn and Zn matrix composite coatings containing nano-sized SiC particles with an average size of 50 nm were prepared from the zinc sulfate bath. The effects of the pulse frequency, maximum current density and duty cycle on the amount of particles embedded were examined. Electron microscopic studies revealed that the coating morphology was modified by the presence of SiC nanoparticles. In the presence of SiC nanoparticles deposit grows in outgrowth mode resulting in a very rough and porous microstructure. However, at very low and very high duty cycles a smooth and pore free microstructure was obtained. Corrosion resistance properties of the coatings were studied using potentiodynamic... 

The sliding frictional contact problem for a laterally graded half-plane has been considered. Two finite element (FE) models, in macro and micro scales have been developed to investigate the effective parameters in contact mechanics of laterally graded materials loaded by flat and triangular rigid stamps. In macro scale model, the laterally graded half-plane is discretized by piecewise homogeneous layers for which the material properties are specified at the centroids by Mori-Tanaka method. In micro scale model, functionally graded material (FGM) structure has been modeled as ideal solid quadrant particles which are spatially distributed in a homogeneous matrix. Boundary conditions and... 

Surface turbulence during the filling of the mold triggers the entrainment of oxide films, which appears to be detrimental to the soundness of the final casting. Nonpressurized and bottom-gating systems have been employed in order to avoid such casting defects by reducing the surface velocity of the liquid metal. However, recent studies have shown that the melt front velocity in the mold entrance may exceed the critical value in the nonpressurized and bottom-gating systems. Therefore, a study was conducted on numerical simulation melt flow pattern in nonpressurized and bottom-gating systems. It was noted that the liquid metal enters the gate and then mold cavity with a higher velocity by... 

The purpose of this paper is to estimate the stiffness and strength of damaged rectangular reinforced concrete shear walls after an earthquake using surface crack patterns. Assessing the damage severity of buildings after an earthquake is an important part of the emergency inspection operation of buildings. Expert inspectors tag buildings into two categories of safe or unsafe that are usually affected by subjective decisions, which may result in catastrophic events reported in previous earthquakes. In this research, an extensive database on the images of damaged rectangular reinforced concrete shear walls (RCSWs) is collected and used to develop predictive equations for updated stiffness and... 

Surface passivation of organic-inorganic halide perovskites (OIHPs) is a crucial step to annihilate the surface defects and to control the deteriorated ion migration phenomenon. Here, we study the role of lead sulfate (PbSO4) as an effective passivator in OIHP single crystals (SCs). Using impedance spectroscopy, we evaluate the ion migration and electrical properties of lead sulfate-passivated methylammonium lead tri-bromide (MAPbBr3) SCs. We found that the low-frequency impedance response that is assigned to the ionic motion in the MAPbBr3 SC is strongly affected by the inorganic PbSO4 surface treatment. The activation energy corresponding to the ion migration of MAPbBr3 SC is increased... 

Surface crack patterns can easily show the behavior of concrete elements and structures. However, visual damage inspection performed by experts is a subjective approach and is prone to inaccuracies. The quantification makes this process objective and more reliable. In that regards, the maximum crack width is used as a practical measurement. It has been shown that the crack width is not a good indicator of damage due to its inherent uncertainties; In fact, it might bounce back after unloading. As such, a dimensionless parameter so-called Fractal Dimension has been introduced as a robust index that can quantify the complexity of crack distribution efficiently. The present study aims to... 

In this article an attempt was made to fabricate defect-free asymmetric polysulfone (PSf) membranes for the separation of oxygen and nitrogen. The approach is based on the enhanced delayed demixing by blending surface modifying macromolecules (SMMs) in the casting solution and by immersing the cast film in isopropanol for a certain period before it is immersed in water. Different SMMs, including hydrophobic and charged SMMs, were synthesized, characterized, and blended to the host PSf. It was found that the charged SMM could indeed contribute to the removal of defective pores from the skin layer and enhancement of oxygen/nitrogen selectivity. The experimental results were further interpreted... 

The van der Walls interaction between a carbon nanotube sheet (CNTS) and a rare gas atom, is studied using both atomistic and continuum approaches. We present analytical expressions for the van der Waals energy of continuous nanotubes interacting with a rare gas atom. It is found that the continuum approach does not properly treat the effect of atomistic configurations on the energy surfaces. The energy barriers are small as compared to the thermal energy, which implies the free motion above the CNTS in heights about one nanometer. In contrast to the energy surface of a graphene sheet, the honeycomb lattice structure in the energy surface of a CNTS is imperceivable. Defects alter the energy... 

Investigation of response of reinforced concrete (RC) structures due to axisymmetric macrocell corrosion of rebars is of concern after propagation of microcracks within the concrete medium. The geometry, boundary and interfaces conditions of the present problem are identical to those stated in part I. As seen in the companion paper, the exact solution to the boundary value problem corresponding to the uncracked steel-rust-concrete composite was possible. After appearance of the microcracks the concrete behavior becomes nonlinear anisotropic with post-cracking softening, and the associated problem is analytically intractable. Therefore, it is proposed to employ a novel meshless method, namely... 

This paper is devoted to the characterization of the surface defects using a recently developed AFM technique named as frequency and force modulation AFM (FFM-AFM). The simulated system includes a recently developed gold coated AFM probe which interacts with a sample including single-atom vacancy and impurities. In order to examine the behavior of the above system including different transition metals, molecular dynamics (MD) simulation with Sutton-Chen (SC) interatomic potential is used. Along this line, an imaging simulation of the probe and sample is performed, and the effects of the horizontal scan speed, the effective frequency set-point, the cantilever stiffness, the tip-sample rest... 

This paper is devoted to the characterization of the surface defects using a recently developed AFM technique called frequency and force modulation AFM (FFM-AFM). The simulated system includes a recently developed gold coated AFM probe which interacts with a sample including single-atom vacancy and impurities. In order to examine the behavior of the above system on different transition metals, the molecular dynamics (MD) simulation with Sutton-Chen (SC) inter-atomic potential is used. In this study, an online imaging simulation of the probe and sample is performed, and the effects of the horizontal scan speed, the effective frequency set-point, the cantilever stiffness, the tip-sample rest... 

Nowadays, gasochromic Pd/WO3 coatings as optically switchable materials during H2 absorption have become more interesting due to their novel applications in smart windows and gas sensor devices. In this study, WO3 films were fabricated by Pulsed Laser Deposition (PLD) on glass substrates. Using an electroless method, Pd nanoparticles were deposited on the surface of the produced films. The effect of Pd growth time on coloring/bleaching rate was studied for different submerging times (1, 2, 5, 10, 15, 20 and 40 min). The best coloring/bleaching velocity was attained with a growth time of 2 min. The effect of growing time and growth feature of Pd particles was further studied using Scanning... 

A mechanochemical method was applied to prepare bismuth oxybromide (BiOBr) nanoplates using bismuth nitrate pentahydrate and potassium bromide for 15 (A15), 30 (A30) and 60 (A60) minutes. Scanning electron microscopy studies showed that all the products were comprised of nanoplates. Aggregated nanoplates along with microblocks were observed for A15 and A30 and the entire morphology was not homogenous. The morphology of A60 was uniform and consisted of thin and isolated nanoplates. Evaluation of the X-ray diffraction patterns showed that the purity and crystallinity of the products improved by increasing the milling time. The energy dispersive X-ray analysis confirmed the high purity of the... 

This paper is devoted to the characterization of the surface defects using a recently developed AFM technique named as frequency and force modulation AFM (FFM-AFM). The simulated system includes a recently developed gold coated AFM probe which interacts with a sample including single-atom vacancy and impurities. In order to examine the behavior of the above system including different transition metals, molecular dynamics (MD) simulation with Sutton-Chen (SC) interatomic potential is used. Along this line, an imaging simulation of the probe and sample is performed, and the effects of the horizontal scan speed, the effective frequency set-point, the cantilever stiffness, the tip-sample rest... 

During the last decade, fabrication of high-quality graphene films by chemical vapor deposition (CVD) for nanoelectronics and optoelectronic applications has attracted increasing attention. However, processing of large-area monolayer and defect-free graphene films is still challenging. In this work, we have studied the effect of processing conditions on the self-limited growth of graphene monolayers on copper foils during low pressure CVD both experimentally and theoretically based on thermokinetics and kinetics of Langmuir adsorption. The effect of copper pre-treatment, growth time, and carbon potential of the atmosphere (indicated by the methane-to-hydrogen gas ratio, r) on the quality of... 

This study investigates the effects of uncertainties in the prediction of creep-fatigue crack propagation in 316L(N) austenitic stainless steel plates containing a semi-elliptical surface defect. Different parameters in geometry, material behavior and test condition are considered as random variables in probabilistic assessments. Monte-Carlo sampling method is employed to estimate the probability distribution of desired outputs such as propagated crack sizes, stress intensity factors and creep rupture life. It is shown that, the standard deviation of the predicted crack sizes in both through-wall direction and along the surface of the plate will be increased by increasing the time (hence the... 

There have been significant advances in fabrication of high-density microelectrode arrays using silicon micromachining technology in neural signal recording systems. The interface between microelectrodes and chemical environment brings great interest to researchers working on extracellular stimulation. This interface is quite complex and must be modeled carefully to match experimental results. Computer simulation is a method to increase the knowledge about these arrays and to this end the finite element method provides a strong environment for investigation of relative changes of the electrical field extension surrounding an electrode positioned in chemical environment. In this paper FEM... 

The purpose of this paper is to quantify the extent of damage of rectangular reinforced concrete shear walls after an earthquake using surface crack patterns. One of the most important tasks after an earthquake is to assess the safety and classify the performance level of buildings. This assessment is usually performed by visual inspection that is prone to significant errors. In this research, an extensive database on the images of damaged rectangular reinforced concrete shear walls is collected from the literature. This database includes more than 200 images from experimental quasi-static cyclic tests. Using the concept of fractal geometry, several probabilistic models are developed by... 

Titanium dioxide (TiO2) is an extensively used electron transporting layer (ETL) in n–i–p perovskite solar cells (PSCs). Although, TiO2 ETL experiences the high surface defect together with low electron extraction ability, which causes severe energy loss and poor stability in the PSC. In this study, a new intermediate layer consisting of gold nanoparticles functionalized with fully conjugated fullerene C60 derivative (C60-BCT@Au NPs) that enhances the interfacial contact at ETL/perovskite interface leading to a perovskite film with improved crystallinity and morphology is reported. Moreover, the studies demonstrate that the interface modification of the TiO2 ETL with C60-BCT@Au NPs...