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The major purpose of the present study was to uncover if the structural complexity of type I and type II conditionals can greatly be mitigated by applying the sandwich format of dynamic assessment (DA). More specifically, this study aimed at investigating the contributory role of DA in improving intermediate EFL learners’ acquisition of conditional structures. To this end, a quasi-experimental pretest- posttest design was utilized. From the target population of students studying English at one of language institutes in Isfahan, two intact classes were selected based on a convenient sampling method. The age of the participants was between 19 and 24. Subsequently, they were randomly assigned to two equal groups receiving their instruction through the present, practice, produce (PPP) method, and the treatment group members were exposed to the sandwich format of DA. The findings revealed that the students in the experimental group significantly outperformed those in the control group on the immediate and delayed post-test. The results indicated that interaction, mediation, and feedback were important factors helping EFL students overcome the challenging task of learning conditionals. Notably, the findings may have important implications for EFL, learners, teachers, and materials developers.

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Electromagnetic forming is a high energy rate forming process which is applied for manufacturing and assembly of many parts that are used in automobile and aerospace industries. In this process, the electromagnetic body forces (Lorentz forces) are used to produce metallic parts. Joining high electrical conductivity parts by using electromagnetic forming process is as an innovative method. Therefore, it is very important to use a proper technique for assuring the quality of the Strength of Electromagnetically Joints. In this article, this process was simulated in ABAQUS. Then geometric, physical and mechanical specifications of the tube and coil are entered to subroutine and the magnetic pressure is obtained and by applying them on tube in ABAQUS software, agent analysis of the process and deformation of the work-piece is obtained. The effective process parameters such as discharge voltage, clearance between the tube and die, wall thickness and length of the tube on depth of bead were experimentally investigated by design of experiment technique based on Taguchi Method and signal to noise. Finally, found very good agreement between simulation and experimental results. The depth of bead in sequential coupled algorithm compared to experimental result had about 4% error.

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In this article, an experimental and theoretical study on the prediction of forming limit diagram (FLD) for aluminum alloy (2024) is developed. To identify and calibrate coefficients of YLD2004-18P, YLD2011-18P, YLD2011-27P and BBC2008-16P advanced yield criteria, tensile tests were performed in seven directions with respect to the rolling direction. Directional yield stresses and anisotropy coefficients were determined. Then, an appropriate error-function was defined and optimized by using Levenberg-Marquardt algorithm. By considering 14, 12, 10 and 8 anisotropy parameters, the effect of number of parameters on the accuracy of yield functions were investigated. The best condition with minimum error can be achieved, when 14 anisotropy parameters are used. To compare the calculated yield stresses and r-values with experimental data, a method presented by Leacock was used. The results have shown that all four criteria give predictions of yield stresses which are nearly close to experimental values. The prediction of yield stresses and anisotropy coefficients by means of YLD2011-27P and YLD2004-18P criteria have more correlation and good agreement with the experimental data, respectively. For obtaining experimental FLD Nakazima test was performed. In order to simulate the necking phenomenon and calculate the limit strains, the modified Marciniak-Kuczynski (MK) model, Swift hardening law and some new yield criteria including YLD2004-18P, YLD2011-18P, YLD2011-27P and BBC2008-16P were utilized. At the right hand side of FLD, YLD2004-18P and YLD2011-27P criteria and also at the left hand side YLD2011-27P criterion have shown better conformity with experimental results.

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In this paper, the effect of different workpiece geometries on the properties of welded Al-7075-T6 parts in rotational friction welding process has been investigated by using experimental and finite element approaches. Welding process is continuous drive friction welding. In this research, the samples diameter were selected equal to 25 mm and the samples length were selected equal to 75 mm. The process variables such as friction time (t1), forging time (t2), friction pressure (P1) and forging pressure (P2) where assumed to be constant, whereas, rotational speeds were variable and selected equal to 2000 rpm and 2500 rpm. Three cylindrical parts with different cross sectional geometries were adopted as three samples. Finally, to verify the accuracy of numerical analysis, the experimental and thermo-mechanical simulation results were compared and found a good agreement between them. Since, an experimental test is a time consuming and a costly process activity, it was decided to get more results by using an alternative method such as finite element simulation technique. Results of this study showed that changing in front geometric of workpiece is an effective factor for tensile strength, length of workpiece and generated flash in welded area and by changing this factor, properties of welded area can be improved.

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In this paper, the effect of extrusion die profile on the dimensional tolerance of a cross section of a part in a forward extrusion process was studied. In these experimental and numerical investigations, some parameters such as extrusion speed, metal flow, extrusion temperature and extrusion force were considered as process variables. The specimen was aluminium alloy 2014 with a variable wall thickness. The variable wall thickness causes the metal flow rate to be changed along the die orifice. As a result, the die which is used to produce this part must be suitable to control the flow rate of metal. In this study, two different dies were used to produce this part. In first die, to control the metal flow, variable bearing length method is used. In the second die, in addition to the bearing length method, a feeder is used in the narrow channels. From the experimental and numerical results, it was found that the first die is not good enough for manufacturing of this part. Because, the first die was not able to control uniform metal flow rate through the die orifice during the extrusion process. This drawback causes the die cavity to remain empty at the sharp corners which results a low quality and low dimensional accuracy in the product, especially in narrow channels. The numerical analysis results have shown that, the second die performance was much better than the first one. It was able to control uniform metal flow rate which causes high quality products.

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In recent years, knee diseases are spread especially in elderly people. Since performing daily activities such as walking and running, the knee supports the weight of the body, there is more likely to be injured. This issue is more important for elderly people who have weak muscles and almost all elderly people suffer from knee pain. One way to help this people in order to move normally is to use a wearable device to aid the knee. In this article, a passive wearable robot will be designed to improve the strength of the elderly who suffers from the knee pain. The robot uses the compliance elements to increase the power of the knee joint in parts of a cycle. This robot will be developed based on a Stephenson II six-bar mechanism. Using this mechanism has the advantage of producing the similar motion to a knee. In other words, this mechanism produces the linear and rotational motions simultaneously. Additionally, more compliance elements can be added to improve the performance of the wearable robot. The optimal dimensions of the robot will be Through the kinematics analysis and also the derivation of the dynamics equations and the numerical validations of these equations, the performance of the robot will be considered. The performance of the robot mounted on the leg is compared with the human. Obtained results show that the less power is required when a wearable robot is used. This proves the merits of the designed robot to be used for the elderly.

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Rotor dynamics is known as the study of vibrational behavior in axially symmetric linear rotating structures. Devices such as engines, turbines, compressors and generators are located in this category. Study of vibrational behavior of these structures in different rotational velocities yields to recognition of critical points and preventing failures, especially high cycle fatigue. The case study of the present paper is a bladed disk used in the first stage of compressor of a gas turbine engine. The material of machined integrated bladed disk is aluminum alloy. The simulations have been done by ANSYS finite element software. By using the cyclic symmetry module of ANSYS the nodal diameter mode shapes of structure have been obtained. In the next step, experimental modal analysis test has been done by measuring 58 points on the bladed disk and the nodal diameters have been obtained experimentally. Finally, experimental and simulation results have been compared to each other. The novelty of this paper is the experimental procedure of obtaining nodal diameter of a bladed disk, which is so useful in verification of numerical simulation.

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Electrohydraulic forming (EHF) is a high velocity sheet metal forming process in which two or more electrodes are positioned in a water filled chamber and a high-voltage discharge between the electrodes generates a high-pressure to form the sheet. In this study extensive experimental tests were carried out to investigate the effect of different parameters (such as discharge energy, stand off distance and electrodes gap) on the maximum drawing depth and implicit on shock wave maximal pressure in electrohydraulic free forming. EHF is a complex phenomenon and experimental work alone is not sufficient to properly understand this process. To explain different aspects of the problem, Arbitrary Lagrangian Eulerian (ALE) formulations coupled with fluid–structure interaction (FSI) algorithms that are available in the advanced finite element code LS-DYNA were used to the numerical simulation. In order to model the effect of the electrical discharge, two different approaches were implemented; explosive equivalent mass and energy leak. In the first approach, According to the similarity between explosion and electrical discharge in the water, electrical discharge energy was converted to equivalent TNT mass. In the second approach electrodes gap is replaced by a plasma channel and electrical discharge energy was leaked to it in a short amount of time which makes the channel expand and generate shock waves propagating toward the workpiece .Finally, it was found a good correlation between the experimental and simulation results.

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Nowadays high velocity forming methods have become popular among industrial companies due to their capability at improving formability in various materials in comparison to conventional methods. Electrohydraulic forming (EHF) is a high velocity sheet metal forming process in which two electrodes are positioned in a water filled chamber and a high-voltage discharge between the electrodes generates a high-pressure to form the sheet metal. In this work, extensive experimental tests have been designed based on design of experiments (DOE) technique to investigate the effective parameters in EHF (with bridge wire between electrodes). Discharge energy, material, length and diameter of bridge wire have been considered as effective input parameters. Response surface methodology (RSM) has been used to model and optimize the EHF performance with respect to drawing depth for Brass 260. Base on the results, it can be stated that maximum drawing depth is obtained when discharge energy is maximum. It was found that the aluminum wire was more efficient than copper and tungsten. There also exists an optimum amount of length and diameter of bridge wire determined according to the process conditions.

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Forming limit diagrams (FLDs) are useful tools for prediction of the instability of sheet in metal forming. The goal of this study is to evaluate the formability of 260 brass alloy sheets under various strain rates (particularly at high strain rate). Three types of experimental procedure were developed: Nakazima test (for determination of the FLD at quasi-static condition), hydrodynamic forming (for determination of the FLD at intermediate strain rate) and Electrohydraulic forming (for determination of high strain rate FLD). Electrohydraulic forming (EHF) is a high velocity sheet metal forming process in which two or more electrodes are positioned in a water filled chamber and a high-voltage discharge between the electrodes generates a high pressure to form the sheet. Arbitrary Lagrangian Eulerian (ALE) formulations coupled with fluid–structure interaction (FSI) algorithms (that are available in the advanced finite element code LS-DYNA) were used to the numerical simulation of process and design of sheet metal specimen geometries. It was found that the forming limits of brass 260 in EHF increased more than 11% relative to the quasi-static. In addition, the formability of this material under the hydrodynamic loading is 4% higher than quasi-static values.

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Curing process of composites results in the formation of residual stress and distortion. According to costs of composites fabrication, simulation of the fabrication process in order to avoid wasting investment is important. A common and simple method of composite fabrication is hand lay-up. In this research plane stress due to temperature change of composite laminates has been investigated and its resultant curvature has been analyzed. So, two symmetric and un-symmetric laminates with eight plies are subjected to 100-degree centigrade temperature change and normal and shear stresses have been calculated. First, by classical lamination theory which is the most important theory in stress analysis of composites, mechanical properties of glass/epoxy composite with 70 percent volume fraction, temperature change and stacking sequence are input variables of the written program. Three in-plane stress component is read and the amount of curvature has achieved that shows it is negligible for the symmetric sample. To validate the residual stress field, finite element simulation for both samples has been done that resulted in finding the same results with negligible errors. Assumptions are considered in finite element modeling and classical lamination theory which result in deviation of outputs from reality. In spite of these assumptions, the thermal simulation of composite laminations in ABAQUS software can have the desired prediction of reality. The innovation of the research is the use of this software and the verification of code.
 

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