Sharif Digital Repository

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 precipitation hardenable materials, it is desirable to determine the precipitate dissolution temperature for homogenizing the microstructure by controlling the size and distribution of the precipitates. In this research, the influence of various heat treatment and hot deformation conditions on the kinetics of γ ′ dissolution and its morphological evolution in Nimonic 115 was studied. In addition, hot deformation behavior of the material was investigated using hot compression experiments at varying temperature (between 1,050°C and 1,175°C) and strain rates (between 0.01 and 1 s-1) up to a true strain of 0.8. The values obtained for the solvus temperature of γ ′ precipitates by two methods... 

A general flow line model is developed to investigate the deformation behavior of Cu and Al through Bc route of Equal Channel Angular Pressing process at curved and sharp dies. Considering the Taylor theory, the obtained strain and strain rate from the flow line model and also using a modified version of ETMB model, the evolutions of nano-structure in the processed Cu and Al are predicted. Comparison between the modeling results and experimental data is carried out and a reasonable agreement is achieved. The results show that the deformation in the sharp die occurs in a narrow zone with higher strain rate than that in the curved die. Also, the cell size of the processed Cu is smaller than... 

In this study, a set of constitutive equation corrected for deformation heating is proposed for a near equiatomic NiTi shape memory alloy using isothermal hot compression tests in temperature range of 700 to 1000 °C and strain rate of 0.001 to 1 s -1. In order to determine the temperature rise due to deformation heating, Abaqus simulation was employed and varied thermal properties were considered in the simulation. The results of hot compression tests showed that at low pre-set temperatures and high strain rates the flow curves exhibit a softening, while after correction of deformation heating the softening is vanished. Using the corrected flow curves, the power-law constitutive equation of... 

The influence of Cu addition on the hot deformation behavior of NiTi shape memory alloys was investigated using hot compression test. A series of alloys with different Cu contents of Ti50.4Ni49.6-xCux (x = 0, 3, 5, 7 at.%) were deformed under compression to a true strain of 0.7 at the temperature range of 700-1000 °C with 100 °C intervals and constant strain rate of 0.1 s-1. The stress-strain curves showed that the addition of Cu to NiTi alloy made the flow curves shift upward. This was confirmed by the calculated critical stress, σc, obtained from inflections in θ-σ plots, which is attributed to the formation of high strength Cu containing precipitates and solid solution hardening caused by... 

In this paper the previous velocity field proposed by the authors for the prediction of strain field and deformation load of circular cross section billet in ECAE process has been extended to take into account the deformation behavior of bimetal circular billet in the same process. Accordingly, using Bezier method, as a robust method for determining the geometry of the streamlines, the strain field developed in the circular bimetal billet is calculated. Then, based on the kinematically admissible velocity and strain fields and using the upper bound theorem the ECAE load is predicted. It was found that at constant inner corner angle of ECAE die, with decreasing of outer curve corner the... 

Abstract: The hot deformation behavior of coarse-grained (CG), ultrafine-grained (UFG), and oxide dispersion-strengthened (ODS) AA6063 is experimentally recognized though carrying out compression tests at different temperatures (300–450 °C) and strain rates (0.01–1 s−1). Microstructural studies conducted by TEM and EBSD indicate that dynamic softening mechanisms including dynamic recovery and dynamic recrystallization become operative in all the investigated materials depending on the regime of deformation. Moreover, the high temperature flow behavior is considerably influenced by the initial grain structure and the presence of reinforcement particles. The constitutive and artificial neural... 

We carry out molecular dynamics simulations of nanoindentation to investigate the effect of cementite size and temperature on the deformation behavior of nanocomposite pearlite composed of alternating ferrite and cementite layers. We find that, instead of the coherent transmission, dislocation propagates by forming a widespread plastic deformation in cementite layer. We also show that increasing temperature enhances the distribution of plastic strain in the ferrite layer, which reduces the stress acting on the cementite layer. Hence, thickening cementite layer or increasing temperature reduces the likelihood of dislocation propagation through the cementite layer. Our finding sheds a light on... 

Molecular dynamics simulations combined with quantitative atomic displacement analyses were performed to study the deformation behaviors of polycrystalline cementite (Fe3C). At low temperature and large grain size, dislocation glide acts as the preferred deformation mechanism. Due to the limited number of slip systems at low temperature, polycrystalline cementite breaks by forming voids at grain boundaries upon tensile loading. When the temperature rises or the grain size reduces, grain boundary sliding becomes the primary mechanism and plastic deformation is accommodated effectively  

Thermo-mechanical responses, developed microstructure, and mechanical properties in friction stir welding (FSW) of artificially aged AA2017 plates were investigated. A finite element analysis was first employed to evaluate hot deformation behavior of the alloy during welding. Also, hardness, yield strength, and microstructure of the welded alloy were examined using the results of the model and experimental testing. It was found that strain and temperature fields during welding are asymmetrically distributed and the maximum temperature locates in advancing side. Furthermore, considerable grain refinement is observed in the stir zone where recrystallized grains in the range of 3 to 8 m are... 

The present paper reports the effects of Nd:YAG laser welding on the microstructure, phase transformation, cyclic deformation behavior, and corrosion resistance of Ti-55 wt.% Ni wire. The results showed that the laser welding altered the microstructure of the weld metal which mainly composed of columnar dendrites grown epitaxially from the fusion line. DSC results indicated that the onset of the transformation temperatures of the weld metal differed from that of the base metal. Cyclic stress-strain behavior of laser-welded NiTi wire was comparable to the as-received material; while a little reduction in the pseudo-elastic property was noted. The weld metal exhibited higher corrosion... 

The effects of initial heat treatments, i.e. solution treating and over ageing, on deformation behavior of an age hardenable Al-Cu-Mg alloy, including mechanical properties and texture evolution, during multi-directional forging (MDF) are investigated. Hardness measurements, electron back scatter diffraction (EBSD) maps, and differential scanning calorimetry (DSC) are carried out. Mechanical behaviors of the alloy in terms of compressive stress and hardness test after MDF are investigated. In both solution treated and over-aged alloys, the compressive stress during MDF shows an increase up to the second pass, and by further straining the flow stress is decreased. However, shear and... 

Over past decades, extensive research has been performed on the measurement of land subsidence as a result of compaction of aquifer. This paper describes results from a new field-monitoring system to evaluate changes in matric suction and temperature profiles in soil layers over an extended time period. The monitoring system used in this study consists of inserting dielectric sensors into a 105 m borehole, drilled in a site in Ardabil Plain, The monitoring results from the site were used to calibrate predictions from HYDRUS-1D. The physical and hydraulic properties of the soil materials in different layers were obtained through performing some soil characteristics and filter paper tests... 

Effect of deformation path change on the static strain aging of low carbon steel was studied in this work. In the first stage, strip samples were subjected to cold rolling processes under different paths with the same total reduction in thickness while the deformation behaviors of the rolled samples were also evaluated using a mathematical analysis. Then, cold-rolled strips were aged in room temperature up to 45 days while hardness and tensile evaluations were performed to assess the mechanical properties of the as-rolled and the aged samples. Finally, the influence of rolling pass schedule on the subsequent strain aging phenomenon was investigated by means of the experimental results and... 

The strengthening behavior of particle reinforced metal-matrix composites is primarily attributed to the dislocation strengthening effect and the load transfer effect. To account for these two effects in a unified way, a new multi-scale approach is developed in this paper incorporating the aspect ratio effect into the geometrically necessary dislocation strengthening relationships. By making use of this multi-scale approach, the deformation behavior of metal-matrix composites (MMCs) and metal-matrix nanocomposites (MMNCs) as a function of size, volume fraction, aspect ratio, etc. of the particles has been investigated. Comparison with the previously proposed models and the available... 

Hyperelastic materials have high deformability and nonlinearity in load-deformation behavior. Based on a phenomenological approach, these materials are treated as a continuum, and a strain energy density is considered to describe their hyperelastic behavior. In this paper, the mechanical behavior characterization of these materials is studied from the continuum viewpoint. For this purpose, the strain energy density is expressed as sum of independent functions of the mutual multiple of principal stretches. These functions are determined by applying the governing postulates on the form of the strain energy density. It is observed that a consistent strain energy density is expressible in terms... 

The behavior of hot extruded Al-6Mg during hot deformation has been studied using hot compression test. The tests were performed at temperatures of 350, 450, and 550°C and strain rates of 0.001, 0.1, and 1s -1. Due to the effects of friction and adiabatic heating generated during compression, the attained true stress-true strain curves have been corrected. After correction of friction effect, the virtual work hardening has been removed from stress-strain curves. The flow stress increases and reaches a steady state after correction of adiabatic heating effect. Corrected curves and microstructural examinations exhibit the occurrence of dynamic recovery during hot compression of the alloy. The... 

Hot compression tests were carried out on a Fe-29Ni-17Co alloy in the temperature range of 900 °C to 1200 °C and at strain rates of 0.001-1 s-1. Dynamic recrystallization was found responsible for flow softening during hot compression. The flow behavior was successfully analyzed by the hyperbolic sine equation and the corresponding material constants A, n and α were determined. The value of apparent activation energy was determined as 423 kJ/mol. The peak and steady state strains showed simple power-law dependence on the Zener-Hollomon parameter. The dynamic recrystallization kinetics was analyzed using Avrami equation and the corresponding exponent was determined to be about 2.7. This... 

Ultrafine-grained (UFG) Al6063 matrix nanocomposites reinforced with nano-size Al2O3 were produced by reactive mechanical alloying and hot powder extrusion method. Microstructural studies were performed by transmission electron microscope (TEM) and electron backscatter diffraction (EBSD). Observation of very small regions with high- and low-angle grain misorientation, i.e. grains and subgrains, showed the formation of UFG Al alloy matrix with an average grain size of ~ 0.37 μm. A uniform distribution of alumina particles with an average size of ~ 100 nm was also achieved. Compression test at various temperatures up to 450 °C was carried out to evaluate the high-temperature strength and hot... 

The deformation behavior of a 49.8 Ni-50.2 Ti (at pct) alloy was investigated using the hot compression test in the temperature range of 700 °C-1100 °C, and strain rate of 0.001 s-1 to 1 s-1. The hot tensile test of the alloy was also considered to assist explaining the related deformation mechanism within the same temperature range and the strain rate of 0.1 s-1. The processing map of the alloy was developed to evaluate the efficiency of hot deformation and to identify the instability regions of the flow. The peak efficiency of 24-28% was achieved at temperature range of 900 °C-1000 °C, and strain rates higher than 0.01 s -1 in the processing map. The hot ductility and the deformation...