Journal of Advanced Materials in Engineering (Esteghlal)

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In this study, the missile staging process by implementing a side-injected jet is simulated numerically. The problem is considered to be axisymmetric and the thin shear layer approximation of Navier-Stokes equations along with an algebraic turbulence model is used in a quasi-static form for the calculations. The free stream corresponds to a very high altitude flight condition with a Mach number of 10 and an injected jet pressure ratio of about 63000. An explicit Godunov-type scheme is used in the calculations, which is second-order in time and space. Computations are performed on the attached and separated geometry for a range of distances between the body and the warhead. The intense interactions between the jet flow and the main free-stream and its overall influences on the warhead aerodynamic loading are finally demonstrated. Keywords: Missile Staging, Jet Interaction flow, TVD Scheme, Riemann problem

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In recent years, active filters have been considered and developed for elimation of harmonics in power networks. Comparing with passive, they are smaller and have better compensating characteristics and resistance to line distortions. In this paper, a novel idea based on adaptive filter theory in presented to develop an active filter to eliminate the distortions of an arbitrary signal. Using this idea, new methods of active power filters, are introduced to remove harmonic distortions in single phase power networks. Stability of these methods are analyzed and the simulation results are shown. Design and implementation of this adaptive active filter are done and the performance and advantages of this technique are affirmed by the practical results. Exact estimation of amplitude, frequency and phase of input signal first harmonic is the most important advantage of this adaptive technique. Furthermore, this method is for canceling the harmonic of any arbitrary signal and can easily be modified for other systems, and three phase networks. Due to its adaptive nature, this technique can adopt itself with variation in environment and system parameters and be adjusted for optimal behaviour. Keywords: Adaptive active filter, ac network, amplitude, Phase and frequency Estimation, Floque theorem, Averaging theorem.

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In this paper, the boundary-based estimation of pressure distribution in the cardiovascular system is investigated using two dimensional flow images. The conventional methods of non-invasive estimation of pressure distribution in the cardiovascular flow domain use the differential form of governing equations. This study evaluates the advantages of using the integral form of the equations in these calculations. The concepts provided with the Boundary Element Method (BEM) together with the boundary-based image segmentation tools are used to develop a fast calculation method. Boundary-based segmentation provides BEM with domain pixel extraction, boundary meshing, wall normal vector calculation, and accurate calculation of boundary element length. The integral form of the governing equations are reviewed in detail and the analytic value of integral constants at singular points are provided. The pressure data on boundary nodes are calculated to obtain the pressure data at every point in the domain. Therefore, the calculation of domain pressure could be considered as a post-processing procedure, which is an advantage of this approach. Both the differential and integral-based formulations are evaluated using mathematical Couette test flow image whose pressure domain is available. The resulting pressure distributions from both methods will be compared. According to the results obtained from this study, the use of BEM for estimating pressure values from a non-invasive flow image has the following advantages: reduced computational domain from two to one dimension, flexible calculation of pressure data at arbitrary points or at finer spatial resolutions, robustness against noise, less concern for its stability and compatibility, accuracy, and lower meshing attempts.

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An Al-Mg-Si-Cu alloy was subjected to tensile testing, both under solutionized and ECAE-ed conditions, using strain rates of 10-4 s-1 to 10-1 s-1 at temperatures of 25 ˚C to 325 ˚C to investigate the dynamic strain aging (DSA) phenomenon in the alloy. Negative strain rate sensitivity (m) and increasing ultimate tensile stress were observed in the DSA region with increasing temperature . Regarding the activation energy of the phenomenon, it was suggested that the process is controlled by the interaction of Mg atoms with mobile dislocations at lower temperatures of DSA occurrence while at higher temperatures, the aggregation of Mg atoms and precipitates of a second phase decreases the amount of Mg atoms in the solid solution, resulting in the inverse DSA effect. Moreover, it was shown that at temperatures greater than 250 ˚C, the ratio of post-uniform to uniform elongation increases with increasing temperature or with decreasing strain rate due to the solute drag of Mg atoms in the Al matrix. Processing the alloy by ECAE transferred the negative m values to lower temperatures and decreased the tendency to DSA at higher temperatures. Calculating the mentioned ratio for the ECAE-ed specimens revealed that the post-uniform elongation dominates the uniform elongation at all examined temperatures and strain rates. Also, it was found that for ECAE-ed specimens, the ratio is not so sensitive to variations of temperature and strain rate.

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This study aims at investigation of the hydrogen damage after dissolution annealing and two-stage aging in aluminum 7075 alloy. Dissolution annealing was performed at 500 to 575 ^°C for duration of 1 to 20 hours. The first stage of two-stage aging was performed at 180, 200 and 220 ^°C for 30 minutes. The second stage was carried out at 120 and 150 ^°C for 10, 15 and 20 hours. Structural characteristics and chemical composition of precipitates was investigated using SEM and EDS methods, respectively. Reduction of the tensile strength in T6 process after hydrogenation reached to 150 MPa, although it decreased only, about 50 MPa in the two-stage process. Overall, tensile strength after hydrogen charging was significantly increased in the two-stage aging compared to the T6 process.

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In the present article, RRA, T73 and T6 heat treatments were carried out to improve mechanical properties of 7075 aluminum alloy and its hardness, tensile and bending strengths were evaluated. For this purpose, solution annealing was performed at 530 ºC for 16 h. For T6 treatment, aging was executed at 150 ºC for 24 h after solution annealing. In T73, aging treatment was done in two stages after solution annealin, at 120 and 180 ºC for 7 and 20 h, respectively. RRA treatment was performed in three stages. The first stage was the same as T6 treatment, the second stage constitutes tempering at 200 ºC for
20 min and in the third stage aging process was repeated like T6 treatment. Evaluation of the microstructures and fractured surfaces were performed with optical microscopes (OM) and scanning electron microscopes (SEM). Energy dispersive spectroscopy (EDS) was used to study the chemical composition of precipitates. Hardness, tensile and bending strength were evaluated according to ASTM E384-11e1, ASTM B557-06 and DIN 50121 standards. RRA treatment increased tensile strength from 466 to 485 MPa and hardness from 110 to 165 Vickers. After T6 treatment, tensile strength increased from 466 to 505 MPa and hardness from 110 to 160 Vickers. In T73 process, the tensile strength remained almost constant (465 MPa) but yield strength increased from 394 to 410 MPa and hardness decreased from 110 to 84 Vickers. The bending strength increased from 797 to 844, 920 and 1030 MPa in T73, RRA and T6 processes, respectively. By applying RRA process in optimized temperature and time, hardness, tensile and bending strengths of 7075 aluminum alloy were enhanced from 5 to 15% compared to that of T6 and T73 processes.

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