- Distinguished full professor in Materials Science and Engineering (Metals Deformation and Forming)edit
In this research the cross-sectional profile of flattened wires after flat rolling are calculated for different reductions. The empirical formulation, analytical formulation and numerical method have been used to predict the... more
In this research the cross-sectional profile of flattened wires after flat rolling are calculated for different reductions. The empirical formulation, analytical formulation and numerical method have been used to predict the cross-sectional profile. Also, the theoretical results are compared with the experimental data. It has been found that the numerical method is able to predict the lateral spread, the width of contact area, and the curvature radius in all ranges of the reduction in height with a good accuracy, while the other methods exhibit a reasonable accuracy only for a limited range of height reduction. All results of the methods show that with increasing the reduction in height, the lateral spread and width of contact area are increased and the curvature radius is decreased. The appropriate ranges of height reductions for each method are recommended
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A novel constitutive equation has been proposed to predict the effect of aging treatment on mechanical properties of AA6082 aluminum alloy. Considering that aging phenomenon affects the distribution of alloying element in matrix, and the... more
A novel constitutive equation has been proposed to predict the effect of aging treatment on mechanical properties of AA6082 aluminum alloy. Considering that aging phenomenon affects the distribution of alloying element in matrix, and the fact that different distribution of alloying elements has different impediments to dislocation movement, a material model based on microstructure, has been developed in this research. A relative volume fraction or mean radius of precipitations is introduced into the flow stress by using the appropriate relationships. The GA-based optimization technique is used to evaluate the material constants within the equations from the uni-axial tensile test data of AA6082 alloy. Finally, using the proposed model with optimized constants, the flow behavior of the alloy at different conditions of heat treatment is predicted. The results predicted by the model showed a good agreement with experimental data, indicating the capability of the model in prediction of ...
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The static strain aging behavior of low carbon steel wires after drawing process is studied. To do so, the wires are austenitized at different temperatures and cooled in different rates. Then the wires are drawn and aged at a specific... more
The static strain aging behavior of low carbon steel wires after drawing process is studied. To do so, the wires are austenitized at different temperatures and cooled in different rates. Then the wires are drawn and aged at a specific temperature and time. Before and after aging of each drawn wire, the hardness distribution at its cross section is measured. The increase in hardness due to aging is called aging index. The results show that the hardness of drawn wire is increased from center to surface of its cross section. However, after aging the hardness is decreased from center to surface. In addition, with increasing the austenitizing temperature, the index is increased. Also, with increasing the cooling rate, the index is decreased. Moreover, the aging index is decreased from center to surface.
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Tensile testing was used to simulate the multistage strain aging occurring in low-C steel during the relatively short intervals between dies in a multiple-die wire-drawing machine. The effects were examined of three simulated... more
Tensile testing was used to simulate the multistage strain aging occurring in low-C steel during the relatively short intervals between dies in a multiple-die wire-drawing machine. The effects were examined of three simulated post-hot-rolling cooling rates and three thermal treatments on the strain-aging susceptibility of a high- and a low-N steel. This was measured by applying a 6 pct tensile
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In this research the deformation of wire in flat rolling process has been investigated. A theoretical relationship has been developed to relate the reduction in height of wire to the width of contact area between the rolls and wire. This... more
In this research the deformation of wire in flat rolling process has been investigated. A theoretical relationship has been developed to relate the reduction in height of wire to the width of contact area between the rolls and wire. This relationship depicts that the width of contact area is proportional to square root of reduction in height of wire. Using
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In this paper, the effects of Equal Channel Angular Pressing process (ECAP) followed by Shot Peening process (SP) on the fatigue properties of 6082 aluminum alloy are investigated. Several samples of the alloy are ECAPed and SPed and then... more
In this paper, the effects of Equal Channel Angular Pressing process (ECAP) followed by Shot Peening process (SP) on the fatigue properties of 6082 aluminum alloy are investigated. Several samples of the alloy are ECAPed and SPed and then their mechanical behavior are characterized using tensile, micro-hardness, and fatigue tests. The results indicate that shot peening and then polishing the specimen after one-pass ECAP is an effective method to improve the fatigue life of the alloy. Moreover, by increasing the number of ECAP passes before shot peening, a local work softening occurs at the subsurface layer, leading to a significant decrease in the fatigue life of the alloy. The results of the fractography studies show that the nucleation of fatigue crack moves from the surface of the specimen to the subsurface in the specimens ECAPed more than one pass and then SPed.
In this research the hot deformation characteristics of 7075 aluminum alloy at temperature range of 200 to 450oC and strain rate range of 0.0003 to 1 s-1has been investigated, using hot compression test. Power dissipation map for hot... more
In this research the hot deformation characteristics of 7075 aluminum alloy at temperature range of 200 to 450oC and strain rate range of 0.0003 to 1 s-1has been investigated, using hot compression test. Power dissipation map for hot working of the alloy was developed on the basis of Dynamic Materials Model. The map displayed a domain of dynamic recrystallization (DRX) occurring in temperature range of 400 to 450°C using strain rate of less than 0.001 s−1. Based on the continuum instability criterion, the alloy exhibited a wide range of flow instabilities at temperatures lower than 300oC. The manifestations of the instabilities were considered to be the adiabatic shear bands, confirmed by optical observations. The best region to deform the alloy for industrial uses was suggested to be 400 to 450oC and the best workability region of the alloy was proposed to be the temperature range of 300 to 350oC in conjunction with the strain rates of less than 0.001s-1.
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In this research, the nonlinear elastic behavior of human extensor apparatus was investigated. To this goal, firstly the best material parameters of hyperelastic strain energy density functions consisting of the Mooney-Rivlin, Ogden,... more
In this research, the nonlinear elastic behavior of human extensor apparatus was investigated. To this goal, firstly the best material parameters of hyperelastic strain energy density functions consisting of the Mooney-Rivlin, Ogden, invariants, and general exponential models were derived for the simple tension experimental data. Due to the significance of stress response in other deformation modes of nonlinear models, the calculated parameters were used to study the pure shear and balance biaxial tension behavior of the extensor apparatus. The results indicated that the Mooney-Rivlin model predicts an unstable behavior in the balance biaxial deformation of the extensor apparatus, while the Ogden order 1 represents a stable behavior, although the fitting of experimental data and theoretical model was not satisfactory. However, the Ogden order 6 model was unstable in the simple tension mode and the Ogden order 5 and general exponential models presented accurate and stable results. In order to reduce the material parameters, the invariants model with four material parameters was investigated and this model presented the minimum error and stable behavior in all deformation modes. The ABAQUS Explicit solver was coupled with the VUMAT subroutine code of the invariants model to simulate the mechanical behavior of the central and terminal slips of the extensor apparatus during the passive finger flexion, which is important in the prediction of boutonniere deformity and chronic mallet finger injuries, respectively. Also, to evaluate the adequacy of constitutive models in simulations, the results of the Ogden order 5 were presented. The difference between the predictions was attributed to the better fittings of the invariants model compared with the Ogden model.
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In this research, the occurrence of dynamic strain aging (DSA) phenomenon during equal channel angular extrusion (ECAE) of a commercial air cooled Al–Mg–Si–Cu alloy is investigated. In order to detect the negative strain rate sensitivity... more
In this research, the occurrence of dynamic strain aging (DSA) phenomenon during equal channel angular extrusion (ECAE) of a commercial air cooled Al–Mg–Si–Cu alloy is investigated. In order to detect the negative strain rate sensitivity behaviour associated with DSA, samples were ECAE-ed at various temperatures and strain rates. Subsequently, the extruded billets were subjected to mechanical and physical tests and
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ABSTRACT A new integrated physically based constitutive model was developed for an age hardenable Al-Mg-Si alloy. The kinetics of precipitation during various stages of aging was modelled. The precipitate features consisted of particle... more
ABSTRACT A new integrated physically based constitutive model was developed for an age hardenable Al-Mg-Si alloy. The kinetics of precipitation during various stages of aging was modelled. The precipitate features consisted of particle radius and volume fraction obtained from the kinetics model, which was used to compute the alloy yield strength/hardness. A published multiinternal variable workhardening model was improved to take into account the effects of solute solution and precipitates on the alloy hardening capacity after performing different cycles of aging treatment. The flow curves and hardness predicted by the model were in good agreement with the experimental results. The model is able to predict the microstructure evolution such as cell/subgrain size and dislocation density in the cell interior during the plastic straining of material at different temper conditions.
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The deformation inhomogeneity in flattened wire produced by the wire flat rolling process is studied. Utilizing the combined Finite and Slab Element Method (FSEM), the effective strain fields in the flattened wire are calculated at... more
The deformation inhomogeneity in flattened wire produced by the wire flat rolling process is studied. Utilizing the combined Finite and Slab Element Method (FSEM), the effective strain fields in the flattened wire are calculated at different reductions in height and frictional conditions and compared with experiment. The calculated and experimental results exhibit that the deformation is inhomogeneous and macroscopic shear
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The present research is concerned with the aluminum layer of a loosely packed tri-layer copper-aluminum-copper composite deformed by ECAE process. Electron back scattered diffraction (EBSD), transmission electron microscope, and X-ray... more
The present research is concerned with the aluminum layer of a loosely packed tri-layer copper-aluminum-copper composite deformed by ECAE process. Electron back scattered diffraction (EBSD), transmission electron microscope, and X-ray technique were employed to investigate the detailed changes occurring in the microtexture, microstructure (cell size and misorientation), and dislocation density evolution during consecutive passes of ECAE process performed on the composite based on route Bc. According to tensile test results, the yield stress of the aluminum layer was increased significantly after application of ECAE throughout the four repeated passes and then slightly decreased. An ultrafine grain size within the range of 500-600 nm was obtained in the Al layer by increasing the thickness of copper layers. It was observed that the reduction of grain size in the aluminum layer is nearly 57% more than that of an ECAE-ed single layer aluminum billet. Also, the grain refinement of the a...
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Page 1. Adiabatic Shear Banding in an Al-Mg-Si Alloy Processed by Equal Channel Angular Pressing Majid Vaseghi 1,2,a , Ali Karimi Taheri 1,b , Ji Hoon Yoo 2,c , Soo Hyun Joo 2,d and Hyoung Seop Kim 2,e 1Department ...
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Page 1. Met. Mater. Int., Vol. 16, No. 3 (2010), pp. 363~369 doi: 10.1007/s12540-010-0604-8 Published 26 June 2010 Upper Bound Analysis of Deformation and Dynamic Ageing Behavior in Elevated Temperature Equal Channel Angular Pressing of... more
Page 1. Met. Mater. Int., Vol. 16, No. 3 (2010), pp. 363~369 doi: 10.1007/s12540-010-0604-8 Published 26 June 2010 Upper Bound Analysis of Deformation and Dynamic Ageing Behavior in Elevated Temperature Equal Channel Angular Pressing of Al-Mg-Si Alloys ...
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ABSTRACT The current study proposes a simple constitutive model that integrates the kinetics of precipitation during static aging and the kinetics of precipitate dissolution during preheating to deformation temperature to predict the hot... more
ABSTRACT The current study proposes a simple constitutive model that integrates the kinetics of precipitation during static aging and the kinetics of precipitate dissolution during preheating to deformation temperature to predict the hot flow behavior of AA6063 alloy. The model relates the flow behavior of the age-hardenable alloy to the alloy chemistry, thermal history as well as deformation temperature, strain, and strain rate by means of a physically based model. Different aging conditions, including supersaturated solid solution and overaging conditions with different deformation parameters, were assessed. Each part of the model was in good agreement with those of experimental and other model results published in the literature.
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ABSTRACT In this paper, dynamic strain aging (DSA) behavior in a temperature range of (25-235 °C) and strain rate range of (10−4-5×10−2 s−1) was investigated using a supersaturated age hardenable aluminum alloy. It was found that two... more
ABSTRACT In this paper, dynamic strain aging (DSA) behavior in a temperature range of (25-235 °C) and strain rate range of (10−4-5×10−2 s−1) was investigated using a supersaturated age hardenable aluminum alloy. It was found that two mechanisms consisted of pinning of solute atoms to mobile dislocations and dynamic precipitation, were responsible for DSA in the testing conditions. The effects of both mechanisms on the macroscopic flow curve were studied using experimental and improved physically based material modeling approaches. It was shown that both phenomena lead to a negative strain rate hardening in the alloy. Dynamic precipitation acting at high temperature results in considerable work hardening and material strengthening. Taking into account these microstructural phenomena, the effects of deformation temperature and strain rate on the macroscopic flow behavior were discussed. The proposed modeling approach could successfully predict the experimental flow curve, possible jerky flow, and the corresponding serration types. Also, the spatial nucleation and propagation of the localized deformation bands along the specimen gauge length were recorded by a digital image correlation method and compared with the proposed model predictions.
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In this paper the velocity and temperature fields during hot strip rolling are determined using a rigid–viscoplastic finite element method together with a microstructural model for handling dynamic phase transformation during hot... more
In this paper the velocity and temperature fields during hot strip rolling are determined using a rigid–viscoplastic finite element method together with a microstructural model for handling dynamic phase transformation during hot deformation. Based on these fields, the strain distributions within the rolled metal at different positions in the deformation zone are estimated. The analysis is capable of considering the
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ABSTRACT In this research, the application of equal channel angular extrusion process to produce both the cold-welded and diffusion-bonded Al/Cu bimetallic rods is assessed. The joints shear strength for both of the methods are measured... more
ABSTRACT In this research, the application of equal channel angular extrusion process to produce both the cold-welded and diffusion-bonded Al/Cu bimetallic rods is assessed. The joints shear strength for both of the methods are measured and compared. The microstructure examinations were also carried out using scanning electron microscope equipped with EDX system and x-ray diffraction analysis. The results exhibit that the strength of the bond in cold-welded specimens is dependent on the amount of stretch and pressure at the materials interface. But in the diffusion-bonded specimens, it is depended on the struggle between the oxidation rate of the mating surfaces accompanied by inter-metallic compounds formation and the aluminum and copper atoms ability to diffuse in the joint interface.
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ABSTRACT In this study, artificial neural network (ANN) was used to model the hot deformation behavior of 7075 aluminum alloy during compression test, in the strain rate range of 0.0003-1 s−1 and temperature range of 200-450 °C. The... more
ABSTRACT In this study, artificial neural network (ANN) was used to model the hot deformation behavior of 7075 aluminum alloy during compression test, in the strain rate range of 0.0003-1 s−1 and temperature range of 200-450 °C. The inputs of the model were temperature, strain rate, and strain, while the output of the model was the flow stress. The feed-forward back-propagation network with two hidden layers was built and successfully trained at different deformation domains by Levenberg-Marquardt training algorithm. Comparative analysis of the results obtained from the hyperbolic sine, the power law constitutive equations, and the ANN shows that the newly developed ANN model has a better performance in predicting the hot deformation behavior of 7075 aluminum alloy.
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In this research, the occurrence of dynamic strain aging (DSA) phenomenon during equal channel angular extrusion (ECAE) of a commercial air cooled Al–Mg–Si–Cu alloy is investigated. In order to detect the negative strain rate sensitivity... more
In this research, the occurrence of dynamic strain aging (DSA) phenomenon during equal channel angular extrusion (ECAE) of a commercial air cooled Al–Mg–Si–Cu alloy is investigated. In order to detect the negative strain rate sensitivity behaviour associated with DSA, samples were ECAE-ed at various temperatures and strain rates. Subsequently, the extruded billets were subjected to mechanical and physical tests and