N. Zarrinfar and A. Saidi,
Volume 21, Issue 2 (1-2003)
Abstract
Titanium carbide is used as an attractive reinforcement to produce particulate metal matrix composites. One of the problems to use this carbide as a reinforcement in copper-based composites is the lack of wetability in Cu-TiC system. This property improves as the C/Ti ratio in carbide decreases.
Problems to use this carbide as a reinforcement in copper-based composites is the lack of wetabiity in Cu-TiC system. This property improves as the C/Ti ratio in carbide decreases.
A practical method is presented in this paper to improve the dispersion of titanium carbide into liquid copper and emphasis is placed on the C/Ti ratio in the carbide. It was observed that the C/Ti ratio in a raw mixture containing only Ti and C was equal to C/Ti ratio in the carbide after synthesis but when copper powder was added to the raw materials, this ratio was higher than the starting value. Regarding the relationship between the titanium carbide lattice parameter and the C/Ti ratio in the carbide and this ratio in the raw mixture, a graph was drawn that related the C/Ti=1, a network of agglomerated TiC particles with the same C/Ti ratio is formed which cannot be dispersed into liquid copper. When this ratio is decreased to 0.3, particulate titanium carbide with C/Ti=0.5 can be easily dispersed into liquid copper.
Keywords: SHS reaction, titanium carbide
M. Alizadeh and H. Edriss,
Volume 21, Issue 2 (1-2003)
Abstract
In recent years many different ways have been investigated by steel producers to increase ductility, impact strength and formability of steels. More important ways are steels with very low amounts of inclusion, small size inclusions and modified inclusions. In this study, experiments have been performed on the API-X42 steel produced by the electric arc furnace in Mobarekeh Steel Co. After the preparation of the melt in the electric arc furnace, it is taped in a 200-ton ladle and ladle treatment was preformed in a ladle furnace (LF) in the steelmaking shop. In this study the effects of amount and the rate of CaSi wire addition on the shape and structure of inclusion were investigated. The optimum conditions for adding CaSi for inclusion shape control were also determined. Scanning electron microscope (SEM) and chemical energy analysis dispersive system (EDS) showed that adding calcium to the melt affects the chemical composition of inclusions present in steel melt. The effects of CaSi wire injection treatment, injection amount and inclusion shape control on the impact property and formability of steel were shown using charpy impact test.
Keywords: Inclusion shape control, calcium treatment, ladle furnace and inclusion modification
M. Shamanian, A. Saatchi, M. Salehi and T. H North,
Volume 21, Issue 2 (1-2003)
Abstract
The metallurgical and mechanical properties of Ti6Al4V/(WC-Co) friction welds have ben investigated. The microstructure close to the bondline comprised a mixture of acicular and equiaxed α plus β phases. The diffusion of elements in the welded specimens has been detected. The fracture strengths of Ti6Al4V/(WC-Co) friction welds markedly improved when the cobalt content in the (WC-Co) carbide substrate increased.
During the three-point bend testing of Ti6Al4V/WC-6wt.%Co welds, the crack initiated at the bondline region at the periphery of the weld and then propagated into the brittle (WC-6wt.%Co) substrate, while with the Ti6Al4V/WC-11 wt.%Co and Ti6Al4V/WC-24wt.%Co welds, the crack initiated and propagated at the bondline region.
Keywords: Friction welding, Ti6Al4V alloy, Cemented tungsten carbide, Microstructure, Fracture strength
M. Oliazadeh, M. Noaparast and R. Dehghan Simakani,
Volume 21, Issue 2 (1-2003)
Abstract
Application of gravity and magnetic separation methods to upgrade low grade Manganese ores from Venaj Mine has been reported elsewhere. This paper discusses the results of flotation tests, as well as combination of flotation and magnetic method to concentrate fine particles (less than 150 microns) of manganese ore. Results obtained from various direct and reverse flotation tests, using different types of reagents, indicated that manganese fines cannot easily be concentrated by flotation.
In this investigation, combination of direct flotation and magnetic separation for fine particles (finer than 150 microns) with 8.36% Mn, 34.11% SiO2, 23.05% Fe2O3 yielded a manganese concentrate with 26.78% Mn, 11.64% SiO2, 20.37% Fe2O3 and 56% recovery. Desliming 10-15 micron particles prior to flotation tests improved product quality and the recovery.
Keywords: Mineral Processing, Flotation, Manganese, Vanarj Mine
A. Shams Nateri, S. H. Amirshahi and M. Latefi,
Volume 21, Issue 2 (1-2003)
Abstract
In the present work the reflection behavior and the color appearance of acrylic yarns, as pile yarns used in carpet and pilled fabrics, are considered along their lengths as well as their cross- sections. Differences between longitudinal and cross-sectional reflection behaviors of yarns are measured in different yarn densities and hues and explained by the geometric model. The results of experimental work show that the average of reflectance and lightness values along yarns' length, with identical hue, are higher than values obtained from their cross-section. Besides, the lightness values of cross-sectional of samples, with identical hue, increase when the density of yarns in holder cell increases. The metric chromas as well as the hue angles of samples, dyed with the same dyestuff are different in two directions and lead to color difference values between 3.35 and 27.84 under D65 Illumination and CIE 1964 standard observer in CIELAB color difference formula. The reflection differences between two directions are analyzed using the geometric model and it is found that they originated from different optical passes through the fibers in the mentioned modes.
Keywords: Reflection behavior, Geometric model, Acrylic yarn
M. Rezaiee – Pajand and S. Payman,
Volume 21, Issue 2 (1-2003)
Abstract
This paper discusses the effective length factor of columns in Khorjini frames. In order to find this factor, a proper approximated method is proposed. In addition, accurate analysis is performed and the results are compared with those from the proposed technique. The comparison demonstrates the accuracy of presented FORMULATIONS. The proposed method is similar to Julian and Lawrence's, which is used for rigid frames.
Keywords: Khorjini Frame, Effective Length, Bifuraction Load, Rotational Stiffness, Matrix Structural Analysis, Column Factor.
M. T. Sattari, S. S. Eslamian and A. Abrishamchi,
Volume 21, Issue 2 (1-2003)
Abstract
Limitations on water resources and the high costs of new hydraulic structure construction intensify the need for an optimum operation of Iranian reservoir systems. For appropriate water distribution and management in a 9-reservoir system on the Kalamarz river, Mianeh basin optimizing mathematical models are applied. Considering the stochastic nature of river discharges and the constant amount of reservoir volume and farmland area, an optimum linear chance constrained model is programmed and run by GAMS software. This model is only used for within-year regulation. Using a linear yield regulation, operation parameters for request months and all reservoirs are derived by the model. Also, the model computes portions of river discharge diverted to each reservoir in different months and outflow from downstream for different months. Results show greater than 60 percent deficit that indicates the lack of sufficient attention to constructing an optimum reservoir volume and extensive development of farmlands for each reservoir.
Keywords: Multi-reservoir system, optimal operation optimizing Models, linear chance constrained model
J. Soltani and F. Katiraei,
Volume 22, Issue 1 (7-2003)
Abstract
In this paper, using a personal computer (PC), the practical implementation of scalar and vector control methods on a three–phase rotor surface- type permanent magnet synchronous machine drive is discussed. Based on the machine dynamic equations and the above control strategies, two block diagrams are presented first for closed-loop speed controlling of the machine drive/system. Then, the design and implementation of hardware circuits for power, insulating, and signal matching stages are explained along with a description of the written software program for the servo drive system control. These circuits are
used to produce the drive inverter switching pulses. To supply the machine drive, the sinusoidal, uniform sampling and step-trapezoidal PWM voltage source inverters are examined. For closed loop speed control of the drive system, the stator currents and rotor speed signals (in scalar control method only the rotor speed) are sampled on-line. After filtering, buffering and matching operations, these signals are transferred to a personal computer port via a high frequency sampling and high resolution A/D converter. It is worth mensioning that both methods of controlling mathematical calculations is done by computer. Finally, the practical and computer simulation results obtained are demonstrated.
Keywords: Machine Drive, Synchronous Machine, Permanent Magnet, Rotor Surface Type, Scalar and Vector Control, Voltage – Source Inverter, Control by PC.
H. Farzanehfard and A. Pakizeh Moghadam,
Volume 22, Issue 1 (7-2003)
Abstract
Soft Switcing techniques have recently been applied in the design of dc-ac converters, in order to achive better performance, higher efficiency, and power density. One of the soft switching techniques uesd in inverters is resonant dc links. These topologies have some disadvantages such as irregular current peaks, large voltage peaks, uncotrollble pulse width, etc. Another soft switching method in inverters is using Quasi –resonant links, which have PWM modulation capability. Inverters with series or parallel Quasi-resonant dc links use several quasi-resonant current or voltage pulses, respectively, to produce PWM modualation. In this paper an inverter with a novel Quasi-resonant series dc link is introduced. This topology enables current source inverters to have characteristics such as resonant pulse peak limition and pulse width controllability. This circuit provides the inverter with two to three ranges of PWM control capability which increases the switching time control in a larger range.
Various operational modes of this novel Quasi-resonant dc link is analyesed and then the circuit losses is calculated. Finally, simulation results by PSPICE software is presented to justify the circuit operation.
Keyword: Inverter, Soft switching, Novel quasi-series resonant link, increasing control areas, Losses
F. Torkamani Azar and M. Zanjani,
Volume 22, Issue 1 (7-2003)
Abstract
Recently, image processing technique and robotic vision are widely applied in fault detection of industrial products as well as document reading. In order to compare the captured images from the target, it is necessary to prepare a perfect image, then matching should be applied. A preprocessing must therefore, be done to correct the samples’ and or camera’s movement which can occur during the capturing of images. The Radon Transform technique is applied in this study which is inherently invariant to any movement, such as dislocation and rotation which leads to scale changing. According to this technique, simple methods are proposed to determine the degree of movement. Results of computer simulation show the priority of the proposed
method to other techniques. The accuracy of the proposed algorithm is less than 0.1 degree and is applicable to different segments such as texts, tables, drawings, …, which are prepared in different writing languages by different devices such as digital camera, scanner, fax, and printer.
Keywords: Image processing, Image matching, Radon Transform, Skew detection documents, Computer application in industry.
A. Gholami and M. Mirzai,
Volume 22, Issue 1 (7-2003)
Abstract
Overhead transmission lines are influenced by different factors which are mostly electrical and mechanical. These factors can cause problems for lines, distortions in network and outage of line. In designing transmission lines mechanical properties are evaluated after selecting a suitable conductor and clearance with regard to electrical properties. In lines designing, an important mechanical parameter for estimating of phase distance is oscillations. Strong wind or ice fall from conductor surfaces or simultaneous presence of ice and wind may cause different oscillations. These oscillations are classified to aeoliane, galloping, and swing. Aeoliane is of high frequency (5-100Hz) and low amplitude (about a few centimeters), galloping is of low frequency (0.1 to 0.3Hz) and high amplitude (about of span sagging), also swing is of horizontal oscillation. In this paper, the mechanism of conductor galloping oscillation and its different types are described. Also these oscillations are simulated on the typical span by personal computer.
Keywords: Galloping, Overhead transmission lines, Single conductors, Modeling
M. R. Banan and A. Fouladi,
Volume 22, Issue 1 (7-2003)
Abstract
This paper presents a new super-element with twelve degrees of freedom for latticed columns. This elements is developed such that it behaves, with an acceptable approximation, in the same manner as a reference model does. The reference model is constructed by using many Solid elements. The cross section area, moments of inertia, shear coefficient and torsoinal rigidity of the developed new element are derived. Since the reference model has a large number of degrees of freedom (especially for nonlinear cases), computation of the equivalent essential parameters of the proposed element is very time consuming, so, a model using only beam elements is also presented. For the super element, a general purpose program is developed that is capable of performing linear and nonlinear analysis of 3D-frames with latticed columns. In order to derive the essential parameters of the proposed super-element, many latticed columns are analyzed while shear deformations are taken into consideration. Using these essential equivalent parameters approximate relations are proposed for the compution of parameters of any latticed column based on geometric characteristics. Finally, to show the accuracy of the proposed element, several examples are presented.
Keywords: Finite elements, Super-element, Latticed column, Shear deformations, 3D-frames
M. Vafaeian,
Volume 22, Issue 1 (7-2003)
Abstract
A finite element program based on elastic –plastic model of Mohr-Coulomb criterion was used to evaluate the bearing capacity coefficients of soil under shallow strip flexible footing . The results were compared with others’ analytical results and it was found that the present study could offer quite consistent and rather precise values for the bearing capacity coefficients .
The effect of different parameters such as E , υ, φ ,ψ ,γ , type of mesh idealization ,type of elements ,type of load distribution at the footing base have been examined and some new results obtained and discussed. The main conclusion can be summarized as : that the values of bearing capacity coefficients for any particular amount of friction angle should not be expressed as a single number solely dependent on the friction angle ,but the accurate values must be considered as the values dependent on some other effective parameters , which have been mentioned above .
Keywords : soil bearing capacity , finite element , Mohr-Coulomb , shallow footing
S. M. Hosseini and E. Sonei,
Volume 22, Issue 1 (7-2003)
Abstract
In this paper, Forchheimer equation is used as the constitutive equation for flow through rockfill, and the non-linear two-dimensional governing equation with free surface is solved by a new finite element method in a fixed grid. The model is verified by applying it to different flow conditions. The first scenario, which is assumed to be one-dimensional with analytical solution available for it, is used to verify the developed code. Other scenarios, which are two-dimensional free surface tests on a laboratory rockfill, are used to verify the model. The model shows satisfactory performance in this regard. For example, on average, a mean absolute relative error of about 2.3%, in terms of pressure head was found to exist between modelling results and observed values. Further capabilities of the model are discussed by simulating overflow through self– spillway rockfill dams.
Keywords: Finite element, Method, Fixed grid, Non-Darcy flow, Non-linear flow, Rock fill dam
M. K. Jafari, M. Davoodi and M. Razzaghi,
Volume 22, Issue 1 (7-2003)
Abstract
There is a worldwide interest in the proper design of embankment dams to resist earthquake loadings. For the first time in Iran, a complete ambient vibration survey due to low-level loads such as wind, machinery activities, low level tectonic activities, and water exit from bottom outlet was performed on Marun embankment dam. These kinds of ambient vibration tests are suitable for manifesting the lower vibration modes of the dam body. Using different signal processing methods such as Power Spectra Density, the results of in-situ tests have been used to evaluate the natural frequencies, mode shapes and modal damping of the dam body. Besides ambient vibration tests, the 3-D modal analysis of the dam body was performed using ANSYS software. The foundation and abutment flexibility effects on dynamic characteristics of the dam body was investigated and the dynamic soil properties were used from Engineer’s report and some empirical relations. Also initial shear modulus of the dam body and foundation materials were evaluated by refraction survey. In this paper, the test procedures, related signal processing results, numerical analysis results and its comparison with the dynamic characteristics of the dam body obtained from the full-scale dynamic tests will be presented. Finally, calibrating procedures of the numerical model (based on increasing the accuracy of dam body geometry, soil and rock material parameters and foundation and abutment flexibility) will be discussed.
Keywords: Embankment Dam, Dynamic Characteristics, Ambient Vibration Test, Modal Analysis
M. Sefid and A. A. Rostami,
Volume 22, Issue 1 (7-2003)
Abstract
Micro-Channel Heat Sink is a heat exchanger which is used to control the temperature of electronic devices with high heat flux. A comprehensive thermal model for the micro-channels should include three dimensional conduction analysis in the solid body together with three dimensional developing fluid flow as well as heat transfer analyses in the fluid section. This paper reports on a research aimed at finding a solution to the problem. Hydrodynamical and thermal entrance lengths were two parameters considered in this solution. The power law model was used which includes both newtonion and non- newtonion fluids.
Finite difference based on control volume with staggered grid with SIMPLE algorithm was applied in which convection terms were estimated using QUICK method. The results showed that the two entrance length parameters are critical in the estimation of Nusselt number.
Keywords: 3-dimensional, Non-Newtonian, Micro channel, Heat Sink, Thermal Resistance
H. Moslemi Naeini, M. Maerefat and M. Soltanpour,
Volume 22, Issue 1 (7-2003)
Abstract
In hot forming process, the workpiece undergoes plastic deformation at high temperature and the microstructure of the workpiece changes according to the plastic deformation. These changes affect the mechanical properties of workpiece. In order to optimize this process, both the plastic deformation of workpiece and its microstructural changes should be taken into consideration. Since material behaviors at elevated temperatures are usually rate-sensitive, the analysis of the hot forming processes requires a thermo-viscoplastic model. In this paper, by coupling the flow stress prediction model developed with finite element analysis of thermo-viscoplastic of the hot upsetting process, temperature, strain rate, flow stress distributions and geometry of the workpiece at each time step can be calculated. At each time step, the strain rate and temperature at each element are obtained. From these values and the history of deformation, the changes in microstructure and flow stress can be determined.
Keywords: Hot forming, Process, Finite element analysis, Flow stress, Microstructure, Hot upsetting process
H. Khaleghi, M. Mirzaee and S. M. H. Karimian,
Volume 22, Issue 1 (7-2003)
Abstract
In this paper an upwind algorithm based on Roe’s scheme is presented for solution of PNS equations. Non iterative-implicit method using finite volume technique is used. The main advantage of this approach, in comparison with similar upwind methods, is reduction of oscillations around sonic line. This advantage causes the present method to be able to analyze supersonic flows with free stream Mach number near to one, where similar upwind methods normally fail. Some two dimensional/ axisymmetric test cases have been computed to validate the present method. These cases are: Hypersonic flow over a 15-degree compression ramp, two-dimensional supersonic flow over a flat plate and axisymmetric supersonic flow over a tangent
ogive. The results are compared with the results of other numerical schemes, such as Beam and Warming scheme
Keywords: Upwind, Navier stokes, Hypersonic
A. Sadough - Vanini,
Volume 22, Issue 1 (7-2003)
Abstract
An analysis of the demands of ULSI and GSI technologies shows the necessity of multi-layer devices to reduction of signal transmission delay time. This reduction is realized by using a better conductor metal, such as Cu and a surrounding insulator with low capacity than actually used, such as Dow Cyclotene 3022. In this paper, the results of evaporated and sputtered Cu to Dow Cyclotene 3022 were studied. After presentation of interfacial reaction that causes adherence, the methods of enhanced adherence as surface modification of polymer by nitrogen plasma have been investigated.
Keywords: Metalization, Cyclotene, Adherence, Plasma, Multi-layer
A. Shirvani and M. Farzin,
Volume 22, Issue 1 (7-2003)
Abstract
In this paper, shear localization due to strain softening in sidepressed cylinders, is inverstigated. Shear localization causes formation of macroscopic shear bands which can be obsserved in the metallographic cross-section. In this paper, for the first time a method is presented in which a simple two-slice model is used to study the formation of shear bands. The results obtained form this model are in perfect agreement with the results obtatained form experimental works for and micrcrostructures in Ti-6242Si alloy.
Keywords: shear Localiation, shear Bands, Two –Slice Model, Titanium Alloy Ti-6242Si
