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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Transactions of Materials Processing
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Journal DOI :
The Korean Society for Technology of Plasticity
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Volume & Issues
Volume 21, Issue 8 - Dec 2012
Volume 21, Issue 7 - Nov 2012
Volume 21, Issue 6 - Oct 2012
Volume 21, Issue 5 - Aug 2012
Volume 21, Issue 4 - Jul 2012
Volume 21, Issue 3 - Jun 2012
Volume 21, Issue 2 - Apr 2012
Volume 21, Issue 1 - Feb 2012
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The Temperature Dependent C-H/V Constitutive Modeling for Magnesium Alloy Sheet
Park, J.H. ; Lee, J.K. ; Kim, H.Y. ;
Transactions of Materials Processing, volume 21, issue 4, 2012, Pages 221~227
DOI : 10.5228/KSTP.2012.21.4.221
The automotive and electronic industries have seriously considered the use of magnesium alloys because of their excellent properties such as strength to weight ratio, EMI shielding capability, etc. However, it is difficult to form magnesium alloys at room temperature because of the mechanical deformation related to twinning. Hence, magnesium alloys are normally formed at elevated temperatures. In this study, a temperature dependent constitutive model, the C-H/V model, for the magnesium alloy AZ31B sheet is proposed. A hardening law based on nonlinear kinematic and H/V(Hollomon/Voce) hardening model is used to properly characterize the Bauschinger effect and the stabilization of the flow stress. Material parameters were determined from a series of uni-axial cyclic experiments(C-T-C) with the temperature ranging between 150 and
. The developed models are fit to experimental data and a comparison is made.
Closed-die Compaction of AZO Powder for FE Simulation of Powder Compaction
Kim, Y.B. ; Lee, J.S. ; Lee, S.M. ; Park, H.J. ; Lee, G.A. ;
Transactions of Materials Processing, volume 21, issue 4, 2012, Pages 228~233
DOI : 10.5228/KSTP.2012.21.4.228
In this study, powder compaction of AZO (alumina doped zinc oxide) powder was performed with a MTS 810 test system using a cylindrical die having a diameter of 10mm. Pressure-density curves were measured based on the load cell and displacement of the punch. The AZO powder compacts with various densities were formed to investigate the mechanical properties such as fracture stress of the AZO powder as a function of the compact density. Two types of compression tests were conducted in order to estimate the fracture stress using different loading paths: a diameteral compression test and a uniaxial compression test. The pressure-density curves of the AZO powder were obtained and the fracture stress of the compacted powders with various densities was estimated. The results show that the compact pressure dramatically increases as the density increases. Based on the experimental results, calibration of the modified Drucker-Prager/Cap model of the AZO powder for use in FE simulations was developed.
Study of Forming Properties for an Edge Thickening Model Using the Finite Element Method
Cho, C.D. ; Kim, Y.J. ;
Transactions of Materials Processing, volume 21, issue 4, 2012, Pages 234~239
DOI : 10.5228/KSTP.2012.21.4.234
This study examines the forming properties and forming loads needed to increase the edge thickness on the external face of a plate using finite element analysis(FEA). Recently, forming optimization techniques within FEA are being extensively used in designing the optimal forming conditions for processes like forging, extrusion, rolling, and spinning. Most of these existing forming operations involve reducing the volume per unit length, but research for increasing volume per unit length is not very extensive. For this study we chose an automotive engine flywheel which is a welded assembly of a plate and a gear with each component having a different thickness. We considered a forming technique to increase the thickness in order to allow the machining of the gear directly on the external face of plate alleviating the need for a weld. To study various forming techniques, we used the finite element method with the flow stress of material and incremental forming steps. We conclude from this study that the analysis of forming properties and forming loads by using the finite element analysis and testing is useful as a method to increase the thickness per unit length.
Texture Evolution of Extruded AZ80 Mg Alloy under Various Compressive Forming Conditions
Yoon, J.H. ; Lee, S.I. ; Lee, J.H. ; Park, S.H. ; Cho, J.H. ;
Transactions of Materials Processing, volume 21, issue 4, 2012, Pages 240~245
DOI : 10.5228/KSTP.2012.21.4.240
With the increasing demand for light-weight materials to reduce fuel consumption, the automobile industry has extensively studied magnesium alloys which are light weight metals. The intrinsic poor formability and poor ductility at ambient temperature due to the hexagonal close-packed (HCP) crystal structure and the associated insufficient number of independent slip systems restricts the practical usage of these alloys. Hot working of magnesium alloys using a forging or extrusion enables net-shape manufacturing with enhanced formability and ductility since there are several operative non-basal slip systems in addition to basal slip plane, which increases the workability. In this research, the thermomechanical properties of AZ80 Mg alloy were obtained by compression testing at the various temperatures and strain rates. Optical microscopy and EBSD were used to study the microstructural behavior such as misorientation distribution and dynamic recrystallization. The results were correlated to the hardening and the softening of the alloy. The experimental data in conjunction with a physical explanation provide the optimal conditions for net-shape forging under hot or warm temperatures through control of the grain refinement and the working conditions.
Quantitative Analysis of Mechano-luminescence and Its Mechanism in SAO
Timilsina, S. ; Lee, C.J. ; Jang, I.Y. ; Kim, J.S. ;
Transactions of Materials Processing, volume 21, issue 4, 2012, Pages 246~251
DOI : 10.5228/KSTP.2012.21.4.246
The mechanism for mechano-luminescence(ML) in SAO phosphor was investigated quantitatively by measuring the emission intensity under three different tensile conditions. It was found that the ML of SAO was strongly dependent on the dynamic loading rate rather than by the applied load itself. The mechano-luminescent emission in SAO was evaluated based on the trap-releasing process. It was found that the shape of the ML curve in the transient regime obtained from the rate equation has good agreement with the experimental data.
Prediction of Deformation Texture Based on a Three-Dimensional Crystal Plasticity Finite Element Method
Jung, K.H. ; Kim, D.K. ; Im, Y.T. ; Lee, Y.S. ;
Transactions of Materials Processing, volume 21, issue 4, 2012, Pages 252~257
DOI : 10.5228/KSTP.2012.21.4.252
Crystallographic texture evolution during forming processes has a significant effect on the anisotropic flow behavior of crystalline material. In this study, a crystal plasticity finite element method (CPFEM), which incorporates the crystal plasticity constitutive law into a three-dimensional finite element method, was used to investigate texture evolution of a face-centered-cubic material - an aluminum alloy. A rate-dependent polycrystalline theory was fully implemented within an in-house program, CAMPform3D. Each integration point in the element was considered to be a polycrystalline aggregate consisting of a large number of grains, and the deformation of each grain in the aggregate was assumed to be the same as the macroscopic deformation of the aggregate. The texture evolution during three different deformation modes - uniaxial tension, uniaxial compression, and plane strain compression - was investigated in terms of pole figures and compared to experimental data available in the literature.
Failure Prediction for an AZ31 Alloy Sheet during Warm Drawing using FEM Combined with Ductile Fracture Criteria
Kim, S.W. ; Lee, Y.S. ;
Transactions of Materials Processing, volume 21, issue 4, 2012, Pages 258~264
DOI : 10.5228/KSTP.2012.21.4.258
The forming failure of AZ31 alloy sheet during deep drawing processes was predicted by the FEM and ductile fracture criteria. Uniaxial tensile tests of round-notched specimens and FE simulations were performed to calculate the critical damage values for three ductile fracture criteria. The critical damage values for each criterion were expressed as a function of strain rate at various temperatures. In order to determine the best criterion for failure prediction, Erichsen cupping test under isothermal conditions at
were conducted. Based on the plastic deformation histories obtained from the FE analysis of the Erichsen cupping tests and the critical damage value curves, the initiation time and location of fracture were predicted under bi-axial tension deformation. The results indicate that the Cockcroft-Latham criterion had good agreement with the experimental data. In addition, the FE analysis combined with the criterion was applied to another deep drawing process using an irregular shaped blank and these additional results were verified with experimental tests.
Process Design of Multi-pass Shape Drawing Considering the Drawing Stress
Kim, S.M. ; Lee, S.K. ; Lee, C.J. ; Kim, B.M. ; Jeong, M.S. ; Kim, B.M. ;
Transactions of Materials Processing, volume 21, issue 4, 2012, Pages 265~270
DOI : 10.5228/KSTP.2012.21.4.265
In this study, a process design method for the multi-pass shape drawing is proposed with consideration of the drawing stress. First, the shape drawing load was calculated to evaluate the shape drawing stress, and the intermediate die shape was determined by using an electric field analysis and the average reduction ratio. In order to evaluate whether material yielding occurs at the die exit, the drawing stress was determined by using the calculated shape drawing load. Finally, FE-analysis and shape drawing experiments were conducted to validate the design of the multi-pass shape drawing process. From the results of the FE-analysis and shape drawing experiments, it was possible to produce a sound shape drawn product with the designed process. The dimensional tolerances of the product were within the allowable tolerances.