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Friction Stir Radial Backward Extrusion (FSRBE) as a new grain refining technique

Jafarzadeh H., Babaei A., Esmaeili-Goldarag F.

Archives of Civil and Mechanical Engineering

2018

Vol. 18, no. 4

1374--1385

A new method entitled Friction Stir Radial Backward Extrusion (FSRBE) is presented for processing fine-grained tubes. In FSRBE technique, an initial pure copper billet is placed inside a cylindrical chamber. The billet is pushed toward a rotating tool which results in radial and backward flow of the material while is frictionally stirred. The microstructure evolution during FSRBE was investigated through experimental observations and cellular automaton (CA) modeling. The observations reveal that the microstructure with initial grain size of 75 μm was refined to a fine-grained structure with an average grain size of 12 μm. The results of tensile tests demonstrate slight improvement in the value of yield and ultimate strength, elongation and microhardness. The microstructural evolution during FSRBE processing in the micro-level was studied using a coupled cellular automaton algorithm and finite element model. First, the macroscopic plastic flow behavior of material during FSRBE was calculated using FEM simulation method. Next, by tracing the plastic strain, the strain rate and temperature, in the deformation domain of cellular automaton, the DRX kinetics of pure copper is obtained in a devised post-processing step. The microstructure observations showed that the proposed model predictions were in reasonably good agreement with the experimentally obtained results.

On Analytical Approximate Solution of the Fractional Type Rosenau-Hyman Equation

Babaei A.

Fundamenta Informaticae

2017

Vol. 151, nr 1/4

135--143

In this paper, an approximate solution of the fractional type Rosenau-Hyman equation according to an appropriate initial condition will be obtained with the help of the reduced differential transform method (RDTM). The fractional derivatives are described in the Caputo sense. Comparing the methodology with the homotopy perturbation method and the variational iteration method will be presented. The results show that solutions obtained by the RDTM are reliable and this method is effective for this type of nonlinear fractional partial differential equations.