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Ahmed, F.,Arshi, N.,Anwar, M.S.,Lee, S.H.,Byon, E.S.,Lyu, N.J.,Koo, B.H. Elsevier 2012 CURRENT APPLIED PHYSICS Vol.12 No.suppl2
We report the preparation of Zn<SUB>1-x</SUB>Ni<SUB>x</SUB>O nanorods through a chemical route using microwave irradiation. The obtained Zn<SUB>1-x</SUB>Ni<SUB>x</SUB>O nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Raman spectroscopy and magnetization measurements. XRD and TEM results showed that the Zn<SUB>1-x</SUB>Ni<SUB>x</SUB>O nanorods have single phase nature with wurtzite structure and Ni was successfully incorporated at Zn site into the ZnO. The shape of the nanorods changed from hexagon (length ~1.5 μm, diameter ~200 nm) to pencil like tip (length ~1 μm, diameter ~80 nm) by only changing the Ni content from 1% to 3% in ZnO. Concerning the Raman scattering spectra, the modification in the intensity of E<SUB>2</SUB><SUP>high</SUP> mode and sub-band edge emissions provides enough evidence for the existence of intrinsic defects associated with the O atoms. Magnetic measurement results revealed that Zn<SUB>1-x</SUB>Ni<SUB>x</SUB>O nanorods show the well-defined ferromagnetic features at room temperature and the value of M<SUB>s</SUB> increased with the increase of Ni concentration.
Deformation Analysis of Micro-Sized Material Using Strain Gradient Plasticity
Byon S.M.,Lee Young-Seog The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.5
To reflect the size effect of material $(1\sim15{\mu}m)$ during plastic deformation of polycrystalline copper, a constitutive equation which includes the strain gradient plasticity theory and intrinsic material length model is coupled with the finite element analysis and applied to plane strain deformation problem. The method of least square has been used to calculate the strain gradient at each element during deformation and the effect of distributed force on the strain gradient is investigated as well. It shows when material size is less than the intrinsic material length $(1.54{\mu}m)$, its deformation behavior is quite different compared with that computed from the conventional plasticity. The generation of strain gradient is greatly suppressed, but it appears again as the material size increases. Results also reveal that the strain gradient leads to deformation hardening. The distributed force plays a role to amplify the strain gradient distribution.
Strain gradient plasticity based finite element analysis of ultra-fine wire drawing process
S. M. Byon,C. H. Moon,Y. Lee 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.12
Steady-state rigid-plastic finite element analysis coupled with strain gradient plasticity theory has been performed to examine the size effect of material on its plastic deformation behavior and find an optimal semi-cone angle of die which minimizes the drawing energy in the ultra-fine wire drawing process. A stream-line tracing method was adopted to calculate strain component at each element and a strain surface function was introduced to compute the equivalent strain gradient of each element. Introduction of this function enables us to use an established FE code without renewal of its main structure. Hence, the constitutive equation in FE formulation is changed to couple the strain gradient plasticity. A series of FE simulation reveals that significant differences in drawing stress are observed when material size approaches its intrinsic material length. When the strain gradient plasticity theory is reflected on the steady-state FE analysis, the optimal semi-cone angle of the die is reduced by 30%. The variation of optimal semi-cone angle is attributable to considerable increment of homogeneous deformation when the material size reaches its intrinsic material length.
Byon, S.M.,Na, D.H.,Lee, Y. Elsevier 2009 Journal of materials processing technology Vol.209 No.9
<P><B>Abstract</B></P><P>We machined work roll with groove worn down as well as groove with no wear. We then performed a pilot hot rod rolling test at temperature of 1000°C using plain carbon steel (0.1% C) as the roll gap decreases from reference roll gap (6.5mm) to 3.5mm. To understand better the effect of roll gap (i.e., section height) adjustment on the exit cross sectional area (ECSA) variation of workpiece in a two-stand groove rolling process with wear is considered, we carried out a series of three dimensional finite element analysis. Results reveal that variation of ECSA is almost linearly proportional to roll gap change while the roll gap decreases from reference roll gap (6.5mm) to 3.5mm. In oval groove rolling, the exit cross sectional shape and area predicted by FEA is in a good agreement with those measured. In round groove rolling, however, some deviations between FEA and experiment are observed because of roll groove geometry coupled with cross sectional shape of incoming workpiece. In the two-stand groove rolling, the effect of roll gap adjustment at each stand on the exit cross section of workpiece is somewhat different, in comparison with single-stand groove rolling. The roll gap adjustment at the previous stand has a more influence on the ECSA of workpiece than that of the next stand.</P>
Deformation Analysis of Micro-Sized Material Using Strain Gradient Plasticity
S. M. Byon,Youngseog Lee 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.5
To reflect the size effect of material (1~15 ㎛) during plastic deformation of polycrystalline copper, a constitutive equation which includes the strain gradient plasticity theory and intrinsic material length model is coupled with the finite element analysis and applied to plane strain deformation problem. The method of least square has been used to calculate the strain gradient at each element during deformation and the effect of distributed force on the strain gradient is investigated as well. It shows when material size is less than the intrinsic material length (1.54 ㎛), its deformation behavior is quite different compared with that computed from the conventional plasticity. The generation of strain gradient is greatly suppressed, but it appears again as the material size increases. Results also reveal that the strain gradient leads to deformation hardening. The distributed force plays a role to amplify the strain gradient distribution.
A semi-analytical model for predicting the wear contour in rod rolling process
Byon, S.M.,Kim, S.I.,Lee, Y. Elsevier 2007 Journal of materials processing technology Vol.191 No.1-3
We developed a model which predicts wear contour of grooved roll in the oval-round (or round-oval) pass rolling process. The wear contour is computed by using the linear interpolation of the radius of curvature of an incoming workpiece, that of roll groove and a weighting function which takes into account roll tonnage. The roll wear contour is measured using an in situ roll wear contour reader developed by POSCO. Results show that predicted wear contours are in agreement with those obtained experimentally.