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Showing 3 results for Karimi Taheri
THEORETICAL AND EXPERIMENTAL EVALUATION OF DISLOCATION DENSITY IN A WORKPIECE AFTER FORMING
A. Karimi Taheri, Kazeminezhad, A. Kiet Tieu,
Volume 4, Issue 1 (winter & spring 2007 2007)
Abstract
Abstract: The theoretical calculation of dislocation density in different regions of a deformed workpiece of 99.99% pure copper has been carried out using different procedures consisting of Finite Element Method (FEM) and hardness measurement. To assess the validity of the results pertaining to these procedures, the dislocation density is experimentally measured utilizing the Differential Scanning Calorimetry (DSC). Comparing the predicted and experimental results, it was found that the average error in prediction of the dislocation density by the hardness measurement and FEM is 12% and 2.5%, respectively. Also, for further confirmation of the evaluated dislocation density of each region of the deformed workpiece, the annealing process was carried out and in the region of higher dislocation density, a finer grain size was observed.
AN INVESTIGATION INTO THE EFFECT OF ECAE PROCESS ON MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF MIDDLE LAYER IN COPPER CLAD ALUMINUM COMPOSITE
B. Tolaminejad, A. Karimi Taheri, H. Arabi, M. Shahmiri,
Volume 6, Issue 4 (Autumn 2009 2009)
Abstract
Abstract: Equal channel angular extrusion (ECAE) is a promising technique for production of ultra fine-grain (UFG) materials of few hundred nanometers size. In this research, the grain refinement of aluminium strip is accelerated by sandwiching it between two copper strips and then subjecting the three strips to ECAE process simultaneously. The loosely packed copper-aluminium-copper laminated billet was passed through ECAE die up to 8 passes using the Bc route. Then, tensile properties and some microstructural characteristics of the aluminium layer were evaluated. The scanning and transmission electron microscopes, and X-ray diffraction were used to characterize the microstructure. The results show that the yield stress of middle layer (Al) is increased significantly by about four times after application of ECAE throughout the four consecutive passes and then it is slightly decreased when more ECAE passes are applied. An ultra fine grain within the range of 500 to 600 nm was obtained in the Al layer by increasing the thickness of the copper layers. It was observed that the reduction of grain size in the aluminium layer is nearly 55% more than that of a ECA-extruded single layer aluminium billet, i.e. extruding a single aluminium strip or a billet without any clad for the same amount of deformation. This behaviour was attributed to the higher rates of dislocations interaction and cell formation and texture development during the ECAE of the laminated composite compared to those of a single billet
THE EFFECT OF AGING TREATMENT ON MECHANICAL PROPERTIES OFAA6082 ALLOY: MODELINGAND EXPERIMENT
N. Anjabin, Karimi Taheri,
Volume 7, Issue 2 (Spring 2010 2010)
Abstract

Abstract:

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 the material flow behavior after different heat

treatment cycles. Also, the calculated flow stress was used for determination of the material property in Abaqus

Software to analyze the uniaxial compression test. The force- displacement curves of the analysis were compared to

the experimental data obtained in the same condition, and a good agreement was found between the two sets of results.

A novel constitutive equation has been proposed to predict the effect of aging treatment on mechanical
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