1,723,364 research outputs found
Analysis of thermal behavior during equal channel multi-angular pressing by the 3-dimensional finite volume method
No full textThermal behavior and heat transfer during equal channel multi-angular pressing process of AZ31 alloy at room temperature were analyzed by using the 3-dimensional finite volume method. The simulations were carried out at different frictional conditions (friction factor m = 0, 0.1 and 0.2), pressing speeds (v = 2 and 20 mm/s), and pressing routes (A, B and C). The pressing speed influences more on the temperature rise of the AZ31 sample than the pressing route and friction condition. The initial temperature 293 K of the AZ31 alloy was increased up to 395 K for 20 mm/s pressing speed during the pressing. (c) 2008 Elsevier B.V. All rights reserved.X1111sciescopu
Densitication modelling for nanocrystalline metallic powders
No full textA model for densification of metallic powders is proposed. It involves viscoplastic constitutive equations based on dislocation density evolution and also accounts for effects of porosity using a pressure-dependent critical density yield criterion. The model was applied to the case of cold compaction of nanocrystalline copper under uniaxial compression conditions. Densification behaviour during powder compaction was simulated using an explicit integration method as applied to the dislocation density evolution and the variation of the relative density of the compact. The model was gauged by comparing the experimental data generated by cylindrical die compaction tests on Cu powder with the simulation results. The model accounts for the grain size and the deformation rate dependence on the densification process. The proposed densification model was implemented into a finite element code. The finite element method was applied to simulating room temperature die compaction of nanocrystalline Cu powder in order to investigate the densification behaviour. (C) 2003 Elsevier B.V. All rights reserved.X111112sciescopu
MULTI-SCALE FINITE ELEMENT SIMULATION OF SEVERE PLASTIC DEFORMATION
No full textThe technique of severe plastic deformation (SPD) enables one to produce metals and alloys with an ultrafine grain size of about 100 nm and less. As the mechanical properties of such ultrafine grained materials are governed by the plastic deformation during the SPD process, the understanding of the stress and strain development in a workpiece is very important for optimizing the SPD process design and for microstructural control. The objectives of this work is to present a constitutive model based on the dislocation density and dislocation cell evolution for large plastic strains as applied to equal channel angular pressing (ECAP). This paper briefly introduces the constitutive model and presents the results obtained with this model for ECAP by the finite element method.X11sciescopu
Biocomposite assemblies on gold surfaces for reagentless enzyme electrodes using functionalized dendrimers as the building block
No full textMicrostructure, grain growth, and hardness during annealing of nanocrystalline Cu powders synthesized via high energy mechanical milling
No full textIn this paper, the microstructure and hardness evolutions of commercially pure Cu subjected to high energy mechanical milling and subsequent annealing treatments in the temperature range of 400-700 degrees C are investigated. The results demonstrated the simultaneous occurrence of recovery, recrystallization, and grain growth during annealing of the nanocrystalline Cu. The volume fraction of the recrystallized grains estimated using the grain orientation spread exhibits lower values as a result of its dynamic recovery at higher temperatures. The normal grain growth in the range of 400-600 degrees C and significant abnormal grain growth at higher temperatures are observed during annealing. As a result of the abnormal grain growth, the microhardness value rapidly decreases for the sample annealed at 700 degrees C. An analysis of the grain growth kinetics using the parabolic equation in the temperature range of 400-600 degrees C reveals a time exponent of n approximate to 2.7 and an activation energy of 72.93 kJ/mol. The calculated activation energy for the grain growth in the nanocrystalline Cu is slightly less than the activation energy required for the lattice diffusion. This low activation energy results from the high microstrain as well as the Zener-pinning mechanism that arises from the finely dispersed impurities drag effect. (C) 2015 Elsevier Ltd. All rights reserved.11147sciescopu
Ring-Constraint High-Pressure Torsion Process
No full textIn this study, a constraint ring around a workpiece was employed in order to develop back pressure in addition to a compressive die pressure in high-pressure torsion (HPT) process. The influence of the constraint ring during the HPT process was analyzed using the finite element method and experimental analyses. Greater back pressure was developed when a ring of a stronger material enveloped the workpiece. In the experiments, fracture of a brittle material [e.g., La-based bulk metallic glass (BMG)], was limited even at large shear strain (similar to 315) during the ring-constraint HPT (RC-HPT) process due to reduced tensile stress at the edge of the deforming BMG workpiece. Furthermore, the RC-HPT process had beneficial effects on powder consolidation and bonding. The RC-HPT process exhibited smaller loss of material than did the conventional semi-constrained HPT process. The Cu disk produced by the powder RC-HPT had smaller grain sizes because back pressure generated more dislocations and finer grain size in the Cu workpiece.110sciescopu
Multiresolution motion estimation for wavelet-based moving-picture coding
No full textThe shift-variant property of the discrete wavelet transform (DWT) makes the motion estimation and compensation inefficient in the wavelet domain. In order to overcome the shift-variant property of the DWT, a low-band-shift (LBS) method has been developed. Using the LBS method in the wavelet domain, two motion estimation and compensation schemes are developed and evaluated. One scheme is the motion estimation and compensation using the LBS method with wavelet-block basis and the other is with band-by-band basis. Both schemes using the LBS method have superior performances to the conventional motion estimation methods in spatial domain or wavelet domain with respect to peak-noise-to-signal ratio (PSNR). The experiment results show that the proposed schemes have PSNR improvements of above 1.0 dB to the full-search method in spatial domain. (C) 2001 Elsevier Science B.V. All rights reserved
Vehicle structural collapse analysis using a finite element limit method
No full textThis paper discusses the collapse behaviour of vehicle structures under quasi-static loading conditions. The finite element limit analysis for three-dimensional structures is formulated based on the duality theorem in plasticity. The analysis considers sequential deformation of structures with work-hardening effects. The collapse analysis for an S-shaped frame is conducted using both the limit analysis program developed here and the commercial code ABAQUS. Results show a good agreement in load-carrying capacity and deformation mode predictions. Example studies also demonstrate that the method presented can be used to identify the weak part of a structure and change its design to enhance the load-carrying capacity and reduce vehicle passenger compartment distortions
Analysis of Three Dimensional Equal Chanel Angular Pressing by Using the Finite Element Method in Conjunction with the Dislocation Cell Based Constitutive Model
No full textDeformation behavior of pure aluminum during equal channel angular pressing (ECAP) was simulated using a three-dimensional version of the finite element method in conjunction with a constitutive model based on the dislocation density and cell evolution. The three-dimensional finite element analyses for the prediction of microstructural features, such as the variation of the dislocation density and the cell size with the number of ECAP, are reported. The calculated stress and strain and their distributions are also investigated for the route Bc ECAP processed pure aluminum. The results of finite element analyses are found to be in good agreement with experimental results for the dislocation cell size. Due to the accumulation of strain throughout the workpiece and an overall trend to saturation in cell size, a decrease of the difference in cell size with the number of passes (1 similar to 4) was predicted.X114sciescopuskc
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