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    Microstructure and mechanical properties of oxide-dispersion strengthened Al6063 alloy with ultra-fine grain structure

    , Article Metallurgical & Materials Transactions. Part A ; Mar2011, Vol. 42 Issue 3, p. 816-824 Asgharzadeh, H ; Simchi, A. (Abdolreza) ; Kim, H. S ; Sharif University of Technology
    The microstructure and mechanical properties of the ultra-fine grained (UFG) Al6063 alloy reinforced with nanometric aluminum oxide nanoparticles (25 nm) were investigated and compared with the coarse-grained (CG) Al6063 alloy (~2 μm). The UFG materials were prepared by mechanical alloying (MA) under high-purity Ar and Ar-5 vol pct O2 atmospheres followed by hot powder extrusion (HPE). The CG alloy was produced by HPE of the gas-atomized Al6063 powder without applying MA. Electron backscatter diffraction under scanning electron microscopy together with transmission electron microscopy studies revealed that the microstructure of the milled powders after HPE consisted of ultra-fine grains... 

    High performance No-fines concrete using Styrene-butadiene latex

    , Article Seventh International Conference on Damage and Fracture Mechanics: Damage and Fracture Mechanics VII, Maui, HI, 16 October 2002 through 18 October 2002 ; Volume 12 , 2003 , Pages 385-394 ; 14626055 (ISSN) Khaloo, A. R ; Khalighi, Y ; Irajian, M ; Sharif University of Technology
    No-fines concrete has considerable drainage property and a relatively low strength. A wide aggregate grading range, with higher percentage of aggregate in lower bound, improves strength properties, however such grading results in lower drainage capability. The objective of this paper is to make high-performance single-sized No-fines Concrete mixes using polymer modification. An experimental program was carried out to study the parameters of water-cement ratio, aggregate-cement ratio, type of polymer, polymer content, setting time and curing period. The test specimens were 6×12 in. cylinders and were cast using hand rodding compaction in accordance with ASTM C 31-69. Initially a proper... 

    Sintering of biocompatible P/M Co-Cr-Mo alloy (F-75) for fabrication of porosity-graded composite structures

    , Article Materials Science and Engineering A ; Volume 472, Issue 1-2 , 2008 , Pages 338-346 ; 09215093 (ISSN) Dourandish, M ; Godlinski, D ; Simchi, A ; Firouzdor, V ; Sharif University of Technology
    Manufacturing of complex-shaped bimetals utilizing two-color powder injection molding (2C-PIM) and three-dimensional printing (3DP) processes, which basically involve sintering of a powder/binder mixture, has been attracted a great interest. This article addresses sintering of biocompatible Co-Cr-Mo alloy for manufacturing stepwise porosity-graded composite structures. Such composite structures provide strength at the core and a porous layer for the tissue growth. To evaluate the process, two grades of gas atomized Co-Cr-Mo powder with an average particle size of 19 and 63 μm were used. Isothermal and non-isothermal sintering behavior of the loose powders under hydrogen and argon... 

    Joining metals by combining mechanical stirring and thermomechanical treatment to form a globular weld structure

    , Article 9th International Conference on Semi-Solid Processing of Alloys and Composites, S2P 2006, Busan, 11 September 2006 through 13 September 2006 ; Volume 116-117 , 2006 , Pages 397-401 ; 10120394 (ISSN); 3908451264 (ISBN); 9783908451266 (ISBN) Amirkhiz, B. S ; Aashuri, H ; Kokabi, A ; Gharacheh, M. A ; Mola, J ; Sharif University of Technology
    Trans Tech Publications Ltd  2006
    A method for joining metals in the semisolid state is presented. A model alloy Sn-15%Pb was used to demonstrate the concept. By presented process, dendritic microstructure of the weld zone can be avoided. Moreover, near-weld zone of the cold worked substrates which is affected by heat would have a globular structure due to a thermomechanical treatment. The two substrates were heated up locally in the joint line to the semisolid temperature range. At this point a stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint. Localized mechanical properties of different zones were examined using Shear Punch Test (SPT), showing a good strength in the weld... 

    Investigation on adult occupant protection in car pole side impact using various material and thickness of side doors and B pillar

    , Article Applied Mechanics and Materials ; Vol. 663, issue , 2014 , p. 579-584 Lilehkoohi, A. H ; Faieza, A. A ; Sahari, B. B ; Halali, M ; Sharif University of Technology
    In this paper the objective is to study the effect of the material and thickness of the side doors and B pillar on crashworthiness and the energy absorbed in order to select a proper material and an optimized thickness to approach a five star car concept based on the Euro New Car Assessment Program (Euro-NCAP) testing Pole Side Impact. In this matter, four materials and five thicknesses have been chosen for the vehicle model and a total of twenty simulations have been conducted. The results showed that the best selected materials and thicknesses were high strength Steel 204M with a thickness of 1.2mm for side doors and 0.65mm for the B pillar, however, it is important to note that this... 

    On the influence of deformation rate and cooling media on the static strain aging of a warm-rolled low carbon steel

    , Article International Journal of Material Forming ; Volume 6, Issue 3 , February , 2013 , Pages 417-422 ; 19606206 (ISSN) Koohbor, B ; Ohadi, D ; Sharif University of Technology
    An investigation was performed on the static strain aging behavior of warm-rolled low carbon steel during a nearly 1-year aging period, from the view point concerning with influence of changing the deformation speed and cooling media. Mechanical response of the examined material during aging period was evaluated through variations occurred in strength and hardness of the warm-deformed steel. It was shown that changing the rolling speed as well as cooling rate, may result in the occurrence of different metallurgical phenomena, consequently altering the aging kinetics of the material. It was also found that by increasing rolling speed, an increase in the value of hardness and UTS takes place,... 

    A comparison between partial discharge propagation in multiple-α and single-α transformer winding

    , Article Electrical Insulation Conference and Electrical Manufacturing Expo, 2005, Indianapolis, IN, 23 October 2005 through 26 October 2005 ; Volume 2005 , 2005 , Pages 108-111 ; 0780391454 (ISBN); 9780780391451 (ISBN) Naderi, M. S ; Vakilian, M ; Blackburn, T. R ; Phung, B.T ; Zhang, H ; Nam O, H ; Naderi, M. S ; Sharif University of Technology
    Power transformers are in service in different environmental, electrical and mechanical conditions. Many experiences have proved that the inner insulation system degradation may pose the transformer to fail while in service. On the other hand, partial discharges (PD) are recognized as the main cause of insulation deterioration process. Therefore, reaching the optimum inner insulation system is one of the challenges a transformer designer is faced with. The solution lies in the correct and accurate modelling of different types of transformer windings. Transformer strength especially during transient conditions is a criterion for transformer insulation designers. This challenge has made... 

    Seismic performance of high-strength concrete square columns confined with carbon fiber reinforced polymers (CFRPs)

    , Article Canadian Journal of Civil Engineering ; Volume 32, Issue 3 , 2005 , Pages 569-578 ; 03151468 (ISSN) Hosseini, A ; Khaloo, A. R ; Fadaee, S ; Sharif University of Technology
    This paper presents the results of an experimental and analytical study on high-strength, reinforced-concrete (RC) columns with different levels of initial ductility enhanced with carbon fiber reinforced polymer (CFRP) wraps. Six square columns 260 mm wide and 1650 mm long were tested under constant axial load and reversed cyclic lateral load. The test specimens were divided into three groups. Groups I and II were designed and detailed according to the requirements of American Concrete Institute ACI318-02 for intermediate-moment frames. Group I was wrapped with CFRP, group II was control specimens, and group III was designed and detailed according to the requirements of ACI318-02 for... 

    An investigation of deformation behavior and bonding strength of bimetal strip during rolling

    , Article Mechanics of Materials ; Volume 37, Issue 5 , 2005 , Pages 531-542 ; 01676636 (ISSN) Manesh, H. D ; Taheri, A. K ; Sharif University of Technology
    A mathematical model for cold rolling of two-layer strip is proposed using the upper bound theorem to investigate the plastic deformation behavior of the strip at the roll gap. The effects of total thickness reduction on the rolling power, rolling force, thickness reductions of each layer, and bonding strength of bimetal strip are discussed. Furthermore, experiments on two-layer strip rolling are conducted by employing aluminum-tin alloy and mild steel as the layers of the two-layer strips. It is found that all of theoretical predictions are in good agreement with the experimental measurements. Through the study, it becomes clear that the proposed analytical model is applicable for... 

    Optimum seismic design of concentrically braced steel frames: Concepts and design procedures

    , Article Journal of Constructional Steel Research ; Volume 61, Issue 2 , 2005 , Pages 151-166 ; 0143974X (ISSN) Moghaddam, H ; Hajirasouliha, I ; Doostan, A ; Sharif University of Technology
    Elsevier BV  2005
    A methodology is presented for optimization of the dynamic response of concentrically braced steel frames subjected to seismic excitation, based on the concept of uniform distribution of deformation. In order to obtain the optimum distribution of structural properties, an iterative optimization procedure has been adopted. In this approach, the structural properties are modified so that inefficient material is gradually shifted from strong to weak areas of a structure. This process is continued until a state of uniform deformation is achieved. It is shown that the seismic performance of such a structure is optimal, and behaves generally better than those designed by conventional methods. In... 

    The hydro-mechanical behavior of infilled rock joints with fill materials in unsaturated conditions

    , Article Geotechnical Special Publication ; Issue 231 , 3-7 March , 2013 , Pages 129-138 ; 08950563 (ISSN) ; 9780784412787 (ISBN) Khosravi, A ; Khosravi, M ; Meehan, C. L ; Sharif University of Technology
    The existence, nature, and frequency of discontinuities in a given rock mass typically govern the overall shear behavior of the rock. The presence of fine materials such as clay and silt within rock joints, whether the product of infilling or natural weathering processes, can have a significant effect on the shear behavior of the rock joint. When assessing the strength of filled rock joints, it is therefore necessary to determine the separate strengths of both the rock and the joint infill material, and to also have a good understanding of the interaction between the two for various joint geometries and levels of infilling. Much of the existing research on the shear strength of filled rock... 

    Failure analysis of a cracked gasoline engine cylinder head

    , Article Journal of Failure Analysis and Prevention ; Volume 12, Issue 3 , 2012 , Pages 286-294 ; 15477029 (ISSN) Azadi, M ; Mafi, A ; Roozban, M ; Moghaddam, F ; Sharif University of Technology
    This article presents a failure analysis on a gasoline engine cylinder head made of aluminum alloy, which has been used in passenger cars. During an endurance test, a crack initiated from the interior wall of a hole in the center of the cylinder head and then propagated through the thickness of the cylinder head. The metallurgical examinations are conducted in the crack origin zone. The results show that there are many casting pores due to poor quality of casting in the failed cylinder head which has certainly played a crucial role in initiating the crack. Finite element analysis of the cylinder head is performed to identify the stress components. Modeling of a bolt for the hole shows that... 

    Comparison on usefulness of two buried pipeline retrofitting methods in earthquake induced landslides with numerical modeling

    , Article Computer Methods and Recent Advances in Geomechanics - Proceedings of the 14th Int. Conference of International Association for Computer Methods and Recent Advances in Geomechanics, IACMAG 2014, 22 September 2014 through 25 September 2014 ; September , 2015 , Pages 1071-1076 ; 9781138001480 (ISBN) Jafarzadeh, F ; Yoosefi, S ; Farahi Jahromi, H ; Samadiyan, M ; Sharif University of Technology
    Taylor and Francis - Balkema  2015
    Landslides have disastrous influence on buried pipeline operation. In order to overcome this phenomenon, many retrofitting solutions have been proposed in literature and practice. This paper concentrates on the solutions which deal with pipe thickness change and rerouting method. As an answer to this,ABAQUS FE program has been used for numerical modeling. Soil-pipe interaction was modeled as hard and frictional contact in normal and tangential directions respectively. Typical geotechnical parameters of Tehran soil and predicted acceleration time history, compatible with Tehran geological condition, have been introduced to program for numerical calculations. Usefulness of two basic proposed... 

    Investigation of wall shear stress related factors in realistic carotid bifurcation geometries and different flow conditions

    , Article Scientia Iranica ; Volume 17, Issue 5 B , 2010 , Pages 358-366 ; 10263098 (ISSN) Jamalian Ardakani, S. S ; Jafarnejad, M ; Firoozabadi, B ; Saidi, M. S ; Sharif University of Technology
    Cardiovascular diseases are one of the major causes of death in the world; atherosclerosis being one aspect. Carotid bifurcation is one of the sites that are vulnerable to this disease. Wall Shear Stress (WSS) is known to be responsible for the process of atherogenesis. In this study, we have simulated the blood flow for Newtonian and non-Newtonian, steady and unsteady, flow conditions in three idealistic and five realistic geometries. A risk factor has been presented based on the results of wall shear stress and, then, a relation was found between geometrical features and the wall shear stress risk factor. Our main conclusions are: 1) The non-Newtonian behavior of blood elevates the value... 

    Contribution of steel fiber as reinforcement to the properties of cement-based concrete: a review

    , Article Computers and Concrete ; Volume 20, Issue 2 , 2017 , Pages 155-164 ; 15988198 (ISSN) Najigivi, A ; Nazerigivi, A ; Nejati, H. R ; Sharif University of Technology
    During the past decades, development of reinforcing materials caused a revolution in the structure of high strength and high performance cement-based concrete. Among the most important and exciting reinforcing materials, Steel Fiber (SF) becomes a widely used in the recent years. The main reason for addition of SF is to enhance the toughness and tensile strength and limit development and propagation of cracks and deformation characteristics of the SF blended concrete. Basically this technique of strengthening the concrete structures considerably modifies the physical and mechanical properties of plain cement-based concrete which is brittle in nature with low flexural and tensile strength... 

    Processing of Al-20Si-5Fe-2X(X=Cu, Ni, Cr) alloys by melt-spinning and hot-pressing

    , Article European International Powder Metallurgy Congress and Exhibition, Euro PM 2008, Mannheim, 29 September 2008 through 1 October 2008 ; Volume 2 , 2008 , Pages 99-104 ; 9781899072033 (ISBN) Rajabi, M ; Simchi, A ; Davami, P ; Sharif University of Technology
    European Powder Metallurgy Association (EPMA)  2008
    Al-20Si-5Fe-2X (X=Cu, Ni, Cr) ribbons were produced by melt-spinning and consolidated by hot pressing at 400°C for 60 min. Optical and transmission electron microscopy (TEM), X-ray diffractometry (XRD), and hardness test were used to evaluate the microstructure and mechanical strength of the ribbons and hot consolidated specimens. The compressive strength of the specimens at ambient and elevated temperatures was also examined. The microstructure of the ribbons exhibited featureless and dendritic zones, and contains spherically-shaped Si particles with an average diameter of 20 nm. After hot-pressing, ultrafine Si (110-150 nm) and iron-containing intermetallic particles were formed. The... 

    Effect of processing parameters on electrical, mechanical and magnetic properties of iron-resin soft magnetic composite

    , Article Powder Metallurgy ; Volume 50, Issue 1 , 2007 , Pages 86-90 ; 00325899 (ISSN) Hemmati, I ; Madaah Hosseini, H. R ; Miraghaei, S ; Sharif University of Technology
    In the present paper, a practical thermal treatment process has been introduced to stress relieve the iron powders in a soft magnetic composite. The composites were pressed and treated at different pressures and temperatures. Also, some of the samples were treated for various periods of time at 200°C. Density, electrical resistivity and transverse rupture strength of the samples were measured and fracture surfaces were studied by SEM. A series of tests were performed to determine the DC magnetic properties of the samples. It has been shown that there are optimum amounts of resin content and compaction pressure and temperature, rather than time is the dominant factor in stress relief of the... 

    Oscillator strength calculations in color centers of diamond and the role of spin

    , Article European Physical Journal B ; Volume 39, Issue 4 , 2004 , Pages 441-446 ; 14346028 (ISSN) Heidari Saani, M ; Vesaghi, M. A ; Esfarjani, K ; Sharif University of Technology
    A generalized Hubbard model based on a molecular approach is used to calculate many electron wavefunctions of diamond vacancies. We have calculated the oscillator strength of the dipole transition rates from the ground states of the neutral and negatively charged vacancies. The ratio of the oscillator strengths is in very good quantitative agreement with the reported optical spectroscopic data. Electronic configurations in the ground and dipole allowed excited states are presented. With the proposed picture, the much larger oscillator strength of the negatively charged vacancy with respect to other experimentally investigated color centers N-V, H3, X3 and H4 is explained  

    Effect of thermal wave propagation on thermoelastic behavior of functionally graded materials in a slab symmetrically surface heated using analytical modeling

    , Article Composites Part B: Engineering ; Vol. 60 , 2014 , pp. 413-422 ; ISSN: 13598368 Molaei Najafabadi, M ; Ahmadian, M. T ; Taati, E ; Sharif University of Technology
    Design and development of FGMs as the heat treatable materials for high-temperature environments with thermal protection require understanding of exact temperature and thermal stress distribution in the transient state. This information is primary tool in the design and optimization of the devices for failure prevention. Frequently FGMs are used in many applications that presumably produce thermal energy transport via wave propagation. In this study, transient non-Fourier temperature and associated thermal stresses in a functionally graded slab symmetrically heated on both sides are determined. Hyperbolic heat conduction equation in terms of heat flux is used for obtaining temperature... 

    Fatigue lifetime of AZ91 magnesium alloy subjected to cyclic thermal and mechanical loadings

    , Article Materials and Design ; Vol. 53, issue , 2014 , pp. 639-644 ; ISSN: 02613069 Azadi, M ; Farrahi, G. H ; Winter, G ; Eichlseder, W ; Sharif University of Technology
    In the present paper, thermo-mechanical fatigue (TMF) and low cycle fatigue (LCF) or isothermal fatigue (IF) lifetimes of a cast magnesium alloy (the AZ91 alloy) were studied. In addition to a heat treatment process (T6), several rare elements were added to the alloy to improve the material strength in the first step. Then, the cyclic behavior of the AZ91 was investigated. For this objective, strain-controlled tension-compression fatigue tests were carried out. The temperature varied between 50 and 200. °C in the out-of-phase (OP) TMF tests. The constraint factor which was defined as the ratio of the mechanical strain to the thermal strain, was set to 75%, 100% and 125%. For LCF tests,...