Papers by Author: G.H. Majzoobi

Abstract: The objective of this work is to evaluate the equivalent plastic strain levels induced by equal channel angular extrusion (ECAE) in an annealed Al-6063 alloy after six passes at a temperature of 200^°C following route A with a constant ram speed of 30 mm/min through a die angle of 90^° between the die channels using the finite element method (FEM). ECAE process is simulated using the DEFORM-3D software through a three-dimensional analysis. Grain refinement is simulated by forcing the element size to zero. It is found that for a very fine mesh the PEEQ converges to 1.046.

Abstract: In this study, annealed AL-6063 alloy was processed by the Equal Channel Angular Extrusion (ECAE) up to 6 passes at a temperature of 200^°c following route A with a constant ram speed of 30 mm/min through a die angle of 90^° between the die channels. The influence of ECAE processing on the evolution of microhardness in the material was studied using Vickers microhardness testing. The detailed analysis was carried out on the samples of as-received, one, two, three, four, five, and six pass conditions. The grain diameter reduced from 45μm to 2.8 μm after 6 passes of ECAE. The results indicated around 90% increase in Microhardness after 5 passes. Hardness of the inner surface where the billet was under compression was slightly higher than that of the mid-surface.

Abstract: Severe plastic deformation (SPD) is one of the processes used to refine the microstructure of materials. Equal Channel Angular Extrusion (ECAE) is the most common method of SPD. In this study, AL-6063grain refinement was performed using the Equal Channel Angular Extrusion method. The material was extruded up to 6 passes at a temperature of 200°C following route A. A suitable die sets equipped with heating elements alongside a thermometer was employed with the intention of extruding the material. Between the two channels, there was an angle of 90^°. The results showed that the material grain average diameter decreased from 45μm to 2.8 μm after 6 passes of the ECAE. The Charpy test was used for measuring the fracture energy of various samples. The fracture toughness was the function of this energy. According to this experiment, the fracture toughness rose as the number of the ECAE process elevated. Moreover, the toughness improved for 90% after 6 passes of the ECAE process.

Abstract: In this work, hydroforming of X-shape pipe connection made of copper is investigated by experiment and numerical simulation. The length of the connection branch is always a concern. The main purpose of the work is the study of the effect of the branch end boundary condition and the load path on the branch height. An elastic material (called the constraint), such as a spring, is used for controlling the branch to grow to a certain extent. It is shown that the branch end condition, if designed properly, gives rise to the considerable increase in the branch length. The increase, however, depends also on the load path which must be determined by experiment or numerical simulation.

Abstract: Identification of the constants of material models is always a concern. In the present work, a combined experimental, numerical and optimization technique is employed to determine the constants of Zerilli-Armstrong model. The experiments are conducted on a compressive Hopkinson bar, the simulations are performed using finite element method and optimization is carried out using genetic algorithm. In the method adopted here, there is no need for experimental stress-strain curve which is always accompanied by restricting phenomenon such as necking in tension and bulging in compression. Instead of stress-strain curve, the difference between the post-deformation profiles of specimens obtained from experiment and the numerical simulations is adopted as the objective function for optimization purposes. The results suggest that the approach introduced in this work can substitute costly instrumentations normally needed for obtaining stress-strain curves at high strain rates and elevated temperature.

Abstract: In the present work, specimens were cut out from St-37 plates with 19 mm thickness. The thickness of plates was reduced to 12.5 mm by milling and grinding operations. Then a standard V-shaped fillet was made on one edge of the plates. Two plates were butt-welded by standard metal arc gas (MAG) welding process. Residual stresses induced by welding were measured on 20 specimens by centre hole drilling. Load controlled axial fatigue tests were carried out to determine the fatigue life of specimens. Crack growth rates were obtained from experiment. Fractography of specimens was performed. Genetic Algorithm (GA) was employed for prediction of residual stress value in weldments using the crack growth rates obtained from experiments. The results show that, by using the measured crack growth rates and GA model, residual stresses can be estimated with a good approximation.