Journal of Advanced Materials in Engineering (Esteghlal)

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In this paper, moment-curvature behavior and ductility of prestressed concrete members based on nonlinear analysis is investigated. Influence of various design parameters on ductility of flexural members is determined according to appropriate materials models for stress-strain curves of concrete, prestressing steel and conventional reinforcements. Parameters studied include reinforcing index (ω ̅), compressive steel ratio, type of prestressing steel and cross-sectional shape of members. The reinforcing index is the most influential parameter on ductility of prestressed members. This variable contains the influence of several other parameters, such as compressive strength of concrete and reinforcing ratio, and links prestressed, ordinary reinforced and partially prestressed concrete sections. For maximum permissible reinforcing index of 0.36β1 based on ACI design code, curvature ductility is between 1.5 to 3.0 and for ω ̅=0.2, which is the maximum value allowed for moment redistribution, ductility is greater than 4.0, and for ω ̅ less than 0.1, a ductility of greater than 10.0 is achievable. Influence of magnitude of ultimate strength of prestressing steel and cross-sectional shape on ductility is insignificant. Confinement has considerable effect on ductility.

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In this paper , the effect of curing time and temperature as well as various primers on durability of high density polyethylene on plain carbon steel have been investigated. The aim is to increase adhesion, improve durability and also to produce a defect-free in order to improve the corrosion resistance of steel substrate. For this purpose, after surface preparation and applying a primer (zinc phosphate, polyvinylalcohol, resol, stearic acid, and polyurethane) polymer coating was applied using electrostatic powder coating system. Coatings having 300 µ thickness were produced and then subjected to primary and secondary curing treatments. In addition to adhesion, ductility, and corrosion tests, quality of coatings were studied using scanning electron microscopy. The results obtained revealed that, surface porosity and uniformity of metal/coating interface is a function of curing time and temperature, as well as of the primers used. The best results obtained after curing for 45 min at 230˚C. The effects of primers were as following: no primers

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This paper introduces an accurate, fast, and applicable method for optimization of slip surfaces in earth slopes. Using Genetic Algorithm (GA), which is one of the modern and non-classic optimization methods, in conjunction with the well -known Bishop applied method, the optimum slip surface in an earth slope is investigated and its corresponding lowest safety factor is determined. Investigations have shown that selection of appropriate variables to define and to solve the problem and determination of a good range for these variables have a profound effect on the speed of convergence in the problem. In the present study, appropriate variables have been defined for solving the problem in a way that the number of repetitions required to reach convergence are considerably reduced by up to 50% compared with other approaches. This has led to a drastic reduction in time and the memory required. The accuracy of the method is shown first by solving examples related to search for optimum failure surfaces of some homogenous, non-homogenous, and earth dam slopes and then by comparison of the results with those of other optimization techniques. In order to show the application of the present method in modern geotechnical engineering, a reinforced earth slope is studied and its failure surface is finally optimized

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Using Electrostatic Spray Coating Technique, Polypropylene Powder (EPD 60R) was applied on carbon steel substrates at room temperature. In order to obtain a uniform coating, steel substrates with powder coatings were heated in a vacuum oven at various temperatures up to 250° C for various periods of time up to 45 min and a pressure of 200 mb. The coatings produced had thicknesses of around 470 microns. In order to modify the chemical structure of this polymer, the powder coatings containing various weight percentages of maleic (anhydride (MA) and a peroxide (TBHP or DCP) were also applied onto the steel substrates under the above conditions. Adhesion strength, wear resistance, and ductility of polymer coatings produced were assessed using ASTM standard methods. Results obtained revealed that the polymer coating containing 5 wt%. MA and 0.1 wt% TBHP had the best mechanical properties. Adhesive strength and wear resistance of this coating were 14.3 kgf and 250.3 cm, at 6 kgf, respectively, under the applied load of 6kg. Results obtained from DSC thermographs and IR Spectroscopy also proved the chemical bond formation (grafting) between the polymer and MA. The mechanical properties of coatings on steel substrate stem from such graftings.

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Polypropylene (PP) has poor adhesion to metals and other surfaces for its chemical structure. Hence, chemical modification of PP is necessary for metal surface coating application. In this research, grafting of maleic anhydride (MA) onto co(propylene-b-ethylene) in the presence of a dicumyl peroxide (DCP) was accomplished in a single screw extruder. Characteristics of the modified polymer were determined by Infra-red Spectroscopy (IR), Scanning Electron Microscopy (SEM), and adhesion test. Maximum grafting of MA was found to be 1.2832% for 1.5 pph of MA. Adhesion test showed that the samples containing 1 pph of MA (degree of grafting is 0.5816%) had better adhesion to steel surface (17.25 kgf).

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In this paper, the effect of TiH2 and CaCO3 blowing agents was investigated on the structure and energy absorption of Al-7%Si-3%SiC composite metal foam by powder compact route. Composition of the foam was prepared from a mixture of Al, SiC and Si powders. Then, precursors were consolidated in H13 die mould by cold and uni-axial pressing at 110 MPa and at room temperature. The pressed precursors were extruded at 500oC, in a 12*24 mm2 cross-section. Then, the precursors were foamed in a 316L-stainless steel tube with diameter and height of 20 mm and 100 mm, respectively, in an electrical resistance furnace. Finally, for micro-structural investigation the samples were cut and polished, and a scanning electron microscope was used to observe the cell wall and surface topology. For calculation and comparison, energy absorption was used in an Instron Hydraulic test machine and the foam samples were compressed at the ramp velocity of 50 mm/minute. Results showed that foams with CaCO3 agent due to having high porosities are more stable than foams with TiH2 agent. Also, the energy absorption for foam with CaCO3 agent is more than foams with TiH2 agents. However, its drainage due to less thickness of wall porosities is better than the foam with CaCO3 agent.

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In this paper, the behavior of energy absorption of crush-boxes, made of Aluminum foam advanced material, was investigated based on foam cellular structure homogeneity. Therefore, thin-walled tubes of Cu-Zn30wt.%.brass alloy with 27 mm diameter and 1 mm thickness were filled with A356-10vol.%SiC-Xwt.%. of TiH2 foam liquid. Foam samples with 1, 1.5, 2wt.%. of TiH2 were prepared by Form Grip into the brass tubes in order to produce crush-box .Then the crush-boxes as energy absorber elements were compressed by un-axial loading and then behaviors of progressive buckling foams were measured. Results showed by decreasing A356-10vol.% SiC foam density from 0.93 to 0.88 and then 0.43 g/cm3, the energy absorption would be changed from 12955 to 13465 and then to 11192 J, respectively. The sample with 1.5wt.% of TiH2 and density of 0.88 g/cm3 had the maximum energy absorption. Also, the results of foams cellular structure images showed that foams of homogenous cellular structure had a sizeable effect on the progressive buckling behavior. We developed a new parameter as "sorting coefficient", which can release the foams cellular structure non-homogeneity, and change the crush-boxes energy absorption during the progressive plastic buckling.

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