Journal of Advanced Materials in Engineering (Esteghlal)

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Although studies on RC beams under shear have a history record of more than 100 years, many important issues in this context still remain that have evaded attention. The aim of the current study is to study a number of these less investigated aspects of the behavior of RC beams under shear. For this purpose, and based on the modified compression field theory, a computer program has been written to study the effects of transverse and longitudinal steel reinforcement and shear span, a/d, on the behavior of RC beams under shear. The results show that the shear capacity of the beam cannot be increased beyond an optimum amount of transverse steel ratio. This paper will try to provide a precise definition of this optimum transverse steel ratio. Another finding of the present study is that increasing tensile longitudinal steel ratio increases the amount of the optimum transverse steel ratio, while increasing a/d decreases the optimum transverse steel ratio.

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The effects of mechanochemical treatment of monoclinic zirconia in high energy planetary ball mill on its phase transformation were investigated. The mechanical treatment in ball mill reduces the grain size, increases microstrain, and causes phase transition to metastable nanostructured tetragonal and cubic phases. XRD and TEM results show considerable amounts of amorphous phase during ball milling. Surface area measurements by BET method over long milling times reveal that ZrO2 particles are agglomerated with an amorphous phase as a binder. The mechanical treatment increases the reactivity of zirconia in chlorine gas. Annealing of ball milled zirconia in the chlorine atmosphere produces oxygen vacancy in zirconia (ZrO2-x) and causes the amorphous phase to be crystallized and to change into cubic and tetragonal phases. The chlorine atmosphere increases the stability temperatures of cubic and tetragonal phases to 800°C and 1000°C, respectively. In this situation, the energy of grain boundary and oxygen vacancy play important roles in the stability of tetragonal and cubic phases.

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In cast aluminum and its alloys, the microstructure varies under different solidification conditions, causing variations in their mechanical properties. These materials are basically produced in sand and metallic molds or through die casting, each of which is associated with a unique solidification regime with significantly different cooling rates so that the resulting microstructure strongly depends on the casting method used. In the present study, the effects of such important solidification parameters as cooling rate, solidification front velocity, and thermal gradient at the solid-liquid interface on secondary dendrite arm spacing were investigated. By a directional solidification system, the mathematical relation between cooling rate and dendrite spacing was extracted for several commercially important aluminum alloys. A neural network model was trained using the experimental values of cooling rates and secondary dendrite arm spacing. Reliable prediction of these values was made from the trained network and their corresponding diagrams were constructed. A good agreement was found between simulation and experimental values. It is concluded that the neural network constructed in this study can be employed to predict the relationship between cooling rate and dendrite arm spacing, which is difficult, if not iompossible, to accomplish experimentally.

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In the present study phase transformation of silicon and silica during milling in different atmospheres was investigated. The silicon powder was subjected to high energy ball milling in ammonia (25%) atmosphere. The milled powder was subsequently annealed at 1200 ◦C for 1 hour. In another test a mixture of AlN and amorphous silica (micro silica) was subjected to high energy ball milling. The milled powder mixture was subsequently annealed at 1200 ◦C for 2 hours. Phase analysis of the as milled and annealed powders was performed by X-ray diffractometery (XRD). Powder morphology was also examined using a scanning electron microscope (SEM). Results showed that ball milling of silicon in ammonia formed an amorphous phase which transformed to quartz on further milling. After annealing quartz, cristobalite and another oxide phase called O phases were developed on XRD patterns. Ball milling of AlN and amorphous silica led to the transformation of amorphous silica to stishovite phase. This process was completed after annealing..

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The initial stages of the  precipitation in a dilute Ni-Al binary alloy, Ni-11.6 at.%Al, were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), electron diffraction and electron microscopy (FEG-SEM and TEM) techniques. Three samples were similarly solution treated and then cooled to room temperature under different cooling rates, 170، 25 and 0.03oCs-1. The results indicate a clearly homogenous  nucleation during rapid quenching which takes place via simultaneous ordering and phase separation. However, by decreasing the cooling rate to 25oCs-1 the nucleation mechanism changes to heterogeneous on the preferred nucleation sites. The capability of the mentioned empirical techniques for studying the initial stages of the γ′ is another subject which is studied in this article.

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The addition of ZrO2 particles to the HA coating has received considerable attention because ZrO2 particles increase the bonding strength between HA coating and substrate. In this study, nanostructured hydroxyapatite (HA)/yttria stabilized zirconia (YSZ) coatings were prepared by a sol–gel method. It was found that at 950ºC, the dominant phases were HA and tetragonal (t)-zirconia in 3YSZ, cubic (c)-zirconia in 8 YSZ and t-c-Zirconia in 5YSZ phases with the small amounts of β-tricalcium phosphate (β-TCP) and CaZrO3. The crystallite size of the coating was about ~20-30 nm for tetragonal and cubic zirconia grain size and 40-80 nm for hydroxyapatite grain size. Crack-free and homogeneous HA/YSZ composite coatings were obtained with no observable defects. In vitro evaluation in 0.9% NaCl showed that Ca2+ dissolution rate of composite coatings was lower than that of pure HA coatings. The decrease in electrochemical performance of these coated samples in comparison with the uncoated type 316L St.St could be associated with chloride ion and water penetration into the coating, transport of ions through the coating, and the subsequent electrochemical reactions at the coating–metal interface.

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Charpy impact energy of functionally graded steels in the form of crack arrester configuration was investigated. Functionally graded steels which contain layers of ferrite, austenite, bainite and/or martensite could be produced by electroslag remelting. The results showed that notch tip position and the distances of notch with respect to the bainite and martensite layers significantly affect the impact energy of the specimens. Generally, the plastic deformation zone ahead of a crack in a functionally graded material depends on the position of the notch tip where according to the direction of gradient slope may increase or decrease. The closer the notch tips to the brittle phase, the smaller the impact energy of the specimen and vice versa. The effect of plastic zone size on impact energy of functionally graded steels was notionally investigated.

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In the last decade, Calcium Titanate has been introduced as a bioceramic with acceptable mechanical and biological properties for orthopaedic implant applications. In this study, CaTiO3 nano-structure coating was produced by sol-gel dip-coating route for biomedical applications. Calcium nitrate and titanium isopropoxide were used as a precursor. After coating process, the specimen was subjected to rapid thermal annealing (RTA) at 800°C. The phase structure, functional groups and surface morphology of coating were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Uniform crack-free nano-structured coatings were obtained with perovskite crystal structure.

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In this work, NiCu and CoCu alloy nanowires were prepared by electrodeposition within nuclear track-etched polycarbonate membranes with the nominal diameter of 30nm. Electrodeposition was carried out under potentiostatic control with three electrodes. In order to grow CoCu nanowires and NiCu nanowires, an electrolyte containing salts of Co and Cu, and an electrolyte containing the salts of Ni and Cu were used respectively. Then, the potentiodynamic behavior of each electrolyte was investigated by its CV curves, and the optimum potentials for the deposition of Ni, Co and Cu were selected according to these curves. A TEM microscope was used to study the structure of the nanowires. The results showed that the crystalline growth is polycrystalline and the diameter of the wires is about 80 nm. Apart from that, some nanowires were deposited under different deposition voltages. EDX analysis showed that the atomic weight of Ni and Co in all samples vanishes in the potentials between -0.5V to -0.8V which indicates that pure Cu atoms are deposited at these voltages. Deposition of Ni and Co starts at more negative voltages such as -0.9 and -0.85 V, respectively.

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In the present study, in-situ synthesis of carbon nanotube/hydroxyapatite nano composite powder with stable homogeneous dispersions of carbon nanotubes (CNTs) was carried out using surfactant as dispersing agent. By applying sol-gel method, dispersion in the hydroxyapatite matrix and its effects on the microstructure were investigated. The chemical and phase composition, structure and morphological and size analyses were performed using XRD, FT-IR, SEM, TEM/SAED/EDX, Raman, UV-Vis spectroscopy and differential scanning calorimetry (DSC). The influences of different dispersing agents (sodium dodecyl sulfate, SDS) as a benchmark for future dispersion experiments) and excitation wavelength are discussed and the results are compared to the commonly used UV-Visible spectroscopic analysis. The results indicated that synthesis of hydroxyapatite particles in the presence of the carbon nanotubes had the best homogenization of the carbon nanotube dispersion and faster crystallization of hydroxyapatite, and the use of SDS for dispersion carbon nanotubes at hydroxyapatite matrix rendered formation of hydroxyapatite coating on CNTs surface. The average crystallite size of heat-treated (at 600°C) samples, estimated by Scherrer,s equation, was found to be ~50-60 nm that was confirmed by TEM.

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The osseointegration of oral implants is related to the early interactions between osteoblastic cells and titanium surface. Chemical surface modification of titanium (Ti) implants is used to improve peri-implant bone growth, bone-to-implant contact, and adhesion strength. Thus, in this study, the surface topography, chemistry, and biocompatibility of polished titanium surface treated with mixed solution of three acids containing hydrochloric acid (HCl)- hydrofluoric acid (HF)- phosphoric acid (H3PO4) were studied under different concentration conditions. Moreover, Osteoblast cell (MG-63) was cultured on the and treated polished titanium surface. Also, in order to investigate titanium surface, SEM, AFM and EDS analyses were carried out. The results revealed that the surface of titanium treated with mixed solution containing the aforesaid acids had higher roughness, cell attachment, and proliferation than the controls

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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 recent years, much research in the field of advanced materials synthesis using the mechanochemical process has been performed. In this study, Al2O3-TiN nanocomposite was produced by the mechanochemical method and using inexpensive material TiO2 (instead of pure titanium which is too expensive). Also, aluminum and titanium oxide powders were used as raw materials. Milling under N2 atmosphere with 5 atmospheric pressure was performed and the products were evaluated by the SEM and XRD. Milling results showed that in the first stage of the synthesis process, titanium oxide is reduced by aluminum and the process continues, producing titanium reaction with nitrogen. When the Al/TiO2 ratio molar is equal to 1.2 and 1.3, after 20 hours of milling, TiN peaks in the XRD appears. Moreover, the results showed that milling leads to the formation of fine and spherical particles.

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In this article, the role of nano-size calcium carbonate in penetration resistance of medium- density polyethylene (PE) was investigated through experiments. In order to study the penetration resistance of PE and its nanocomposites, perforation test was carried out. The results of tests showed that penetration resistance depends strongly on calcium carbonate amount. As a matter of fact, addition of CaCO3 to PE increases resistance against penetration as CaCO3 amount reaches to 5 percent of weight. Stereomicroscope was used to evaluate the damage and plastic zone around the perforated area in all the samples including neat polyethylene and its nanocomposites. The plastic zone was measured using an image analysis as an effective technique. The results of image analysis techniques proved that the addition of calcium carbonate to PE makes a damaged zone around the perforated area. The results of microscopic evaluations showed that the area of plastic zone rises as the amount of calcium carbonate increases up to 7.5 percent of weight. By increasing the amount of CaCO3, resistance against penetration decreases more and some micro cracks appear around the perforated area. For further clarification of the fracture mechanism of MDPE nanocomposites, scanning electron microscopy was employed. Fracture surface images showed that when calcium carbonate is higher than 5 percent of weight, agglomeration of nanoparticles occurs, resulting in lower resistance against penetration to the samples.

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In this paper, bare spot defects in hot-dip galvanized sheets were studied in terms of the microstructure and their influence on the corrosion and mechanical properties. Surface characteristics and microstructural features were examined by scanning electron microscopy equipped with energy dispersive spectroscopy microanalysis system. The results showed that the major cause of the bare spots was the lack of wetability of the sheet surface due to contamination, improper heat treatment or chemical composition. Corrosion resistance was evaluated by standard salt spray test. Mechanical properties were examined by tensile testing. The time to red rust was much shorter on the bare spots as compared to other regions, but it appeared that bare spot defects had no significant effect on the mechanical properties of the galvanized steel sheets.

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In the present work, thermal and mechanical behaviors of phenolic resin are investigated. This polymer can be used as a matrix for carbon-carbon composites. To find out the best heating process, five different cycles are used for curing the polymer and flexural strength of the specimens are obtained. The cycle with maximum strength is used for the next steps. Then, the oxidation behavior of specimens is studied at different temperatures. The results show that the polymer can withstand temperature about 350°C without significant weight changes. Carbonization of phenolic resin is studied by four different cycles at 1100°C. Oxidation of carbon obtained from carbonization cycle is analyzed extensively and shows no weight change until 550°C. The microstructure of specimens is also investigated by SEM. By additining SiC micro particles to phenolic polymer, the strength change is achieved.

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The aim of this work was synthesis of MCM-41/HA nanocomposite and biodegradation behavior of pure silica-mesoporous in attendance of hydroxyapatite crystals. These materials were synthsized by sol-gel method and ageing at 100°C for 24hr. A surfactant was used as template. The pores were formed after removal of surfactant by calcination at 550°C. FTIR results demonstrated formation of silanol and siloxan groups of silica network and hydroxyl and phosphate groups of HA network. Also SEM, TEM and EDS results confirmed presence of HA crystals within MCM-41 structure. Finally biodegradation behavior was examined by ICP and FTIR analysis. The results indicated biodegradable HA phase in the nanocomposite (with release of Ca2+ inos in water and the increasing of the pH value) can increase non-bridging oxygens of the silica network and therefore, it improves biodegradation behavior of silica network.