Sharif Digital Repository

This paper focuses on creep properties of AZ91-RE and heat treated AZ91 magnesium alloy. Influence of heat treatment and rare earths addition on microstructure and mechanical properties were investigated. Creep behavior is dependent on the stability of the near grain boundary microstructure and is improved by rare earth addition. The results show that sliding of grain boundaries has an important part in the deformation mechanism in AZ91 alloy at elevated temperatures which is greatly suppressed by the rare earths addition  

Alkali-activated binders have been proposed and have emerged as an alternative to ordinary Portland cement (OPC) binders with acceptable mechanical and durability performances in addition to positive environmental impacts. These alternative binders use a wide range of aluminosilicate precursors, with differing availabilities, reactivities, costs and CO2 emissions. Despite all the studies published on improving the characteristics of these materials in the last decades, some aspects of alkali-activated binders require further investigations. For instance, shrinkage in alkali-activated binders due to the different chemical processes being involved is more complicated than OPC composites and it... 

An experimental study of wear characteristics of electroless Ni-10% P coating sliding against hard AISI 52100 steel pin is investigated. Experiments are carried out at room and 550°C temperatures. Heat treatment effects on tribological behavior of this coating are studied. The wear surface and the microstructure of the coatings are analyzed using optical microscopy, scanning electron microscopy, energy dispersion analysis X-ray, and microhardness testing equipment. It is observed that the forming of continuous oxide film on contacting surfaces of pin and disk improves wear resistance and decreases friction coefficient of the Ni-10% P coating. The results indicate that the wear resistance of... 

In a typical surveillance radar, decision about the existence of a target in certain range-azimuth-elevation cell is made from the echo received in current scan, while still there is useful information in history of that range cell that is not considered in decision making. Based on the potential of the Hough Transform to use history of both range and Doppler information, a new method to increase the probability of detection in surveillance radars is proposed. The new method uses a 3D data space and a special projection to detect targets and extract range, speed, and acceleration of maneuvering targets simultaneously  

The main attempt of this paper is to present a new methodology to model a generic low-level flight close to terrain, which guarantees terrain collision avoidance. Benefiting the advantages of high-speed computer technology, this method uses satellite elevation maps to generate so-called "quad-tree forms". The latter is then used to find the optimal trajectories for low-level flights. The novelty of this approach, entitled the "cost map," lies in the integration of aircraft dynamics into the segmented map. This procedure results in some near-optimal trajectories with respect to aircraft dynamics that could easily be used for minimization of flight path together with pilot effort. Different... 

The main attempt of this paper is to present a new methodology to model a generic low-level flight close to terrain, which guarantees terrain collision avoidance. Benefiting the advantages of high-speed computer technology, this method uses satellite elevation maps to generate so called 'Quad-tree forms'. The latter is then used to find the optimal trajectories for low-level flights. The novelty of this approach, entitled the 'cost map', lies in the integration of aircraft dynamics into the segmented map. This procedure results in some near-optimal trajectories with respect to aircraft dynamics that could easily be used for minimization of flight path together with pilot effort. Different... 

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... 

The purpose of this study was the production of copolymers and terpolymers with highly hydrophilic–hydrophobic properties, using inexpensive and available monomers as potential enhancing oil recovery (EOR) and water production control agents for high-temperature and high-salinity (HTHS) oil reservoirs. For this purpose, several copolymers and terpolymers with different molar percentage of acrylamide/styrene, acrylamide/maleic anhydride, and acrylamide/styrene/maleic anhydride were synthesized by the inverse emulsion polymerization technique. The presence of hydrophobic styrene and hydrophilic maleic anhydride monomers in the copolymer and terpolymer structure, provided some unique properties... 

A simple bio-conjugation procedure to surround a single horseradish peroxidase (HRP) enzyme molecule with dendritic polyester macromolecules (polyester-32-hydroxyl-1-carboxyl bis-MPA dendron, generation 5) was proposed. The characterization of resultant nanoparticles entitled HRP dendrozyme, was performed by transmission electron microscopy, dynamic light scattering, gel permeation chromatography and Fourier transform infrared spectroscopy. The results showed that HRP nanoparticles were spherical in shape and have an average size of 14 ± 2. nm in diameter. Furthermore, bio-conformational characterization of HRP dendrozyme was performed by means of circular dichroism and fluorescence... 

A new innovative 'universal' structural joint with multiple applications was devised. The two major conceived contexts for the use of this joint are 'joining beams to columns, ' and 'joining diagonal braces to horizontal ones. ' The main features of this joint are its high rotational capacity, its high shear deformation capacity, its high energy-dissipation capacity, its ability to contain damage, and its repalceability. Due to its geometry, it can well lend itself to protection measures against fire, normally practiced by the involving industries. This makes it a good candidate for being used in structures related to oil and gas industry, offshore or onshore. Through numerical modelling of... 

Due to high vulnerability of steel structures to elevated temperatures and the need for taking adequate and effective measures to reduce human and financial losses in fires, a thorough understanding of such behaviour is of utmost importance. In this research, a half-scale 3D model, comprising moment-resisting frames, equipped with flush end-plate connections, in one direction, and braced frames in the other, was subjected to a scaled ISO 834 standard fire. The maximum attained temperature was 1055 °C. The results showed that the structure tolerates high temperatures for an appreciable amount of time before collapsing. Moreover, for thick flush end-plates, which were used in this study, the... 

The compressive performance of glass fiber reinforced polymer (GFRP) profiles subjected to elevated temperature was investigated through a large number of (3 0 0) tests. The effects of profile cross-sectional area, slenderness, and temperature on the behavior of the GFRP profiles at temperatures ranging from 25 to 400 °C were determined. It was observed that the compressive strength of the GFRP profiles has been decreased by half as the temperature exceeded 90 °C, i.e., close to the glass transition temperature of the matrix. The temperature and ratio of cross-sectional area to external perimeter were determined as two major parameters affecting section capacity. © 2020 Elsevier Ltd  

LiNi0.8Co0.1Mn0.1O2 (NCM811) has been considered as a promising cathode for Li-ion batteries (LIBs) due to its high electrochemical capacity and low cost; however, poor cycling stability is one of the main restricting factors in industrial applications of the NCM811 cathode material. Notably, the capacity fading and low structural stability of NCM811 are intensified at elevated temperatures. ZrO2- and composite rGO-ZrO2-coated NCM811 were fabricated by a facile wet chemical method and evaluated at 25 and 55 °C to overcome these impediments. The ZrO2 coating provides superior cycling and thermal stability and perfectly protects the cathode active material from deleterious side reactions, and... 

Estimating precipitation at high spatial-temporal resolution is vital in manifold hydrological, meteorological and water management applications, especially over areas with un-gauged networks and regions where water resources are on the wane. This study aims to evaluate five downscaling methods to determine the accuracy and efficiency of which on generating high-resolution precipitation data at annual and monthly scales. To establish precipitation-Land surface characteristics relationship, environmental factors, including Normalized Difference Vegetation Index (NDVI), Land Surface Temperature (LST) and Digital Elevation Model (DEM), were considered as proxies in the spatial downscaling... 

In this study, the effects of fiber type (i.e., carbon and glass fibers) and intumescent paint on the tensile performance of fiber reinforced polymer (FRP) sheets at elevated temperatures are investigated. For this purpose, a series of tensile tests were conducted on the glass and carbon fiber reinforced polymer (GFRP and CFRP) sheets, with and without intumescent fire retardant paint, at different elevated temperatures. The studied temperatures ranged from 25 °C to 600 °C. Scanning electron microscopy was also used to examine the effects of elevated temperatures on FRP sheets and the fire protecting mechanism of the intumescent paint. Based on the test results, the tensile strength of the... 

This study was aimed at gaining an improved understanding of the behavior of glass fiber-reinforced polymer laminates at elevated temperatures by means of testing laminate specimens with unidirectional, woven, and randomly distributed (chopped strand mat) fibers. The testing parameters were temperature, the type of fiber, and the thickness of the laminates. The failure modes of the specimens and their elasticity moduli at ambient temperature were investigated, and analysis of variance was conducted to determine the contribution of each parameter to the behavioral test results. The findings showed that among the parameters, an increase in temperature exerted the strongest effect on the... 

This paper investigates the influence of intumescent paint on the performance of FRP bars subjected to low (25–450 °C) and severe (450–800 °C) elevated temperatures. In this research, glass and carbon FRP bars with epoxy resin and coated with nitrogen-based intumescent paint were used. In addition to the temperature effects, a variety of FRP bar diameters were employed to determine its effect on the tensile behavior of FRP bars in the presence of intumescent paint. Further, Bayesian regression methods and ANOVA (ANalysis Of VAriance) were applied on the results to develop a predictive model form and quantify the contribution of the variables in the tensile performance of FRP bars,... 

Interactive vibrations and buckling of double current-carrying strips (DCCS) are investigated in this study. Considering the rotational and transverse deformation of the strip, four coupled equations of motion are obtained using Hamilton’s principle. Using the Galerkin method, mass and stiffness matrices are extracted and the stability of the system is determined by solving the eigenvalue problem. Effects of pretension and elevated temperature on the stability of DCCS are studied for three types of materials and various arrangements. Finally, the effect of horizontal or vertical distance between strips on the critical current value is investigated. According to the results, the effects of... 

Interactive vibrations and buckling of double current-carrying strips (DCCS) are investigated in this study. Considering the rotational and transverse deformation of the strip, four coupled equations of motion are obtained using Hamilton’s principle. Using the Galerkin method, mass and stiffness matrices are extracted and the stability of the system is determined by solving the eigenvalue problem. Effects of pretension and elevated temperature on the stability of DCCS are studied for three types of materials and various arrangements. Finally, the effect of horizontal or vertical distance between strips on the critical current value is investigated. According to the results, the effects of... 

Fin stabilizers are very important device for controlling the ship roll motion against the external moments due to wave. This paper presents numerical results for flow field simulation and the hydrodynamic performance of fin stabilizer attached to a ship hull with free surface effects. Combination of CFD and RANS method has been used for this study. The fin is nonrectangular NACA0015 profile section with a finite aspect ratio. The numerical results include pressure distributions and flow field around the fin which are used to calculate lift coefficients and free surface elevation as the main interest. Some results are compared with available experimental and numerical data in literature and...