http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
초내열 합금 Alloy718의 저주기 피로시험에서 반복연화 및 R=X (X=0,-1)효과
최병학,신수근,신정근,김선화,윤기봉,염종택,박노광 국립7개대학공동논문집간행위원회 2005 공업기술연구 Vol.5 No.-
The LCF properties for R=0 as tension-tension and R=-1 as tension-compression were examined in DA alloy718. While the hysteresis loops composed of ?ε_(t), ?ε_(p) and ?σ were figured with similaity in both of R=0 and R=-1, the loops of R=0 were continuely going down along the stress axis during cyclic fatigue progressing. It was caused by Bauschinger effect, which includes a tendancy for stress recovering as an amount of compression stress. The phenomena of cyclic softening in both of R=0 and R=1 seem to be caused by planar slip of dislocations, which was accompanied by shearing the γ'/γ" precipitates during the cyclic fatigue test.
Ring-rolling design for a large-scale ring product of Ti–6Al–4V alloy
Yeom, Jong Taek,Kim, Jeoung Han,Park, Nho Kwang,Choi, Seung Sik,Lee, Chong Soo Elsevier 2007 Journal of materials processing technology Vol. No.
<P><B>Abstract</B></P><P>The ring-rolling design for a large-scale ring product of Ti–6Al–4V alloy was investigated by a calculation method and FEM analysis. The ring-rolling design includes geometry design (rolled ring dimensions, blank and billet size, etc.) and optimization of process variables. The design criteria are to achieve minimal forming loads, uniform distributions of strain and temperature, and defect-free ring products. In order to predict the forming defects such as the flow localization or instability, shear bands and surface cracks, the processing-map approach considering flow instability was used with FEM simulation. The experimental analysis based on the flow instability map approach was carried out to predict the formation of rolling defects in plane-rolled Ti–6Al–4V rings. An optimum process design to obtain sound Ti–6Al–4V rings without forming defects was suggested and its validation was made by the comparison between the experimental data and FE analysis results.</P>
Finite-element analysis of microstructure evolution in the cogging of an Alloy 718 ingot
Yeom, Jong Taek,Lee, Chong Soo,Kim, Jeoung Han,Park, Nho-Kwang Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>Microstructural changes during the cogging of an Alloy 718 ignot processed by (vacuum induction melting)/(vacuum arc re-melting) were predicted using the combined approach of three-dimensional finite element simulation and modeling for the recrystallization and grain growth. In order to establish recrystallization and grain growth models for Alloy 718 ingot, hot compression and isothermal heat treatment tests were carried out at different temperatures and strain rates. The constitutive equations for metadynamic and static-recrystallization behavior were generated using the experimental data collected from various references. From the experimental results, it was found that the dissolution temperature of δ-phase (Ni<SUB>3</SUB>Nb) played an important role in the microstructural refinement of Alloy 718 ingot. The predicted grain size and its distribution were compared with the microstructures of the cogged billet, and the reliability of the prediction was discussed.</P>
Creep Strain and Creep-Life Prediction for Alloy 718 Using the Omega Method
Yeom, Jong-Taek,Kim, Jong-Yup,Na, Young-Sang,Park, Nho-Kwang 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.6
The creep behavior of Alloy 718 was investigated in relation to the MPCs omega (Ω) method. To evaluate the creep model and determine material parameters, constant load creep tests were performed at different initial stresses in a temperature range between 550 ℃ and 700 ℃. The imaginary initial strain rate (ε_(o) ) and omega (Ω), considered to be important variables in the model, were expressed as a function of initial stress and temperature. For these variables, power-law and hyperbolic sine-law equations were used as constitutive equations for the creep of Alloy 718. To consider the effect of γ" coarsening leading to a radical drop of tensile strength and creep strength at temperatures above 650 ℃, different material constants at the temperatures above 650 ℃ were applied. The reliability of the models was investigated in relation to the creep curve and creep life.
Ring-Rolling Design of Yaw Ring for Wind Turbines
Jong-Taek Yeom,Jeoung Han Kim,Jae-Keun Hong,Jin Mo Lee,Kook Joo Kim,Tae Ok Kim,Nam Yong Kim,Hi Sang Chang 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.3
In this work, a ring-rolling process to formulate ring-shaped components for a wind turbine is designed bymeans of a simulation and in an experimental approach. The target of the ring-rolling design is a yaw ringwith an outer diameter of approximately 3,130 mm. The ring-rolling design includes the design of the geometryand the optimization of the process variables. A calculation method was used for the geometry design, in thiscase for the initial billet and the pre-form (or blank) sizes, and for the final rolled ring shape. Also, a deformationmap-based approach was utilized to determine the initial ring-rolling temperature and feed rate of themandrel. A three-dimensional finite element method was used to predict the formation of rolling defects and thedeformed shape in the ring-rolled components. The design criteria are to achieve uniform distributions of thestrains and temperatures as well as defect-free ring-shaped components. Finally, an optimum process design toobtain a sound large-scale yaw ring without defects is proposed. It is validated by comparisons betweenthe experimental data and the FE analysis results.
Characterization of Friction Welding for IN713LC and AISI 4140 Steel
Yeom, Jong Taek,Park, J.H.,Lee, J.W.,Park, Nho Kwang Trans Tech Publications, Ltd. 2004 Materials science forum Vol.449 No.-
<P>Friction welding of dissimilar materials, Ni-base superalloy IN713LC and oil-quench plus tempered AISI 4140 steel, was investigated. Friction welding was carried out with various process variables such as friction pressure and time. The quality of welded joints was tested by applying bending stresses in an appropriate jig. Microstructures of the heat-affected zone (HAZ) were investigated along with micro-hardness tests over the friction weld joints. DEFORM-2D FE code was used to simulate the effect of welding variables in friction welding process on the distributions of the state variables such as strain, strain rate and temperature. The formation of the metal burr during the friction welding process was successfully simulated, and the temperature distribution in the heat-affected zone indicated a good agreement with the variation of the microstructures in the HAZ.</P>
Process Design of Profile Ring Rolling for Turbine Diaphragm Using FEM Simulation
Yeom, Jong Taek,Jung, Eun Jeoung,Kim, Jeoung Han,Lee, Dong Geun,Park, Nho Kwang,Choi, Seung Sik,Lee, Chong Soo Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.345-346 No.-
<P>The process design of profile ring rolling for a large-scale turbine diaphragm was made using the calculation method and three dimensional finite element method (FEM). The design criteria are to achieve uniform distributions of strain and temperature, and defect-free profiled ring products. Based on the compression test results of the low alloy steel, deformation processing map was generated using the combination of the dynamic materials model (DMM) and stable or unstable forming criteria. The processing map was used to determine the optimum ring rolling temperature and feed rate of the mandrel. FEM analysis was simulated to predict the formation of rolling defects and deformed shape in the profile ring rolled diaphragm product. Finally, optimum process design to obtain a sound large-scale turbine diaphragm without forming defects was suggested and its validation was made by the comparison between the experimental data and FE analysis results.</P>
Anisotropic twinning and slip behaviors and their relative activities in rolled alpha-phase titanium
Won, Jong Woo,Choi, Seong-Woo,Yeom, Jong-Taek,Hyun, Young-Taek,Lee, Chong Soo,Park, Sung Hyuk Elsevier Sequoia 2017 Materials science & engineering Structural materia Vol.698 No.-
<P><B>Abstract</B></P> <P>Loading-direction-dependent anisotropic behaviors of twinning and dislocation slip of rolled alpha-phase titanium (<I>α</I>-Ti) were investigated via uniaxial compression tests performed along three orthogonal directions (the rolling direction (RD), transverse direction (TD), and normal direction (ND)). The initial texture with basal poles inclined at ~30° from the ND toward the TD caused the angle relationship between the <I>c</I>-axis and the loading axis, which governed the Schmid factor (SF) for twinning and slip systems, to differ with the applied loading direction. Analyses of the SF and Taylor axis along with electron backscatter diffraction measurements revealed the dominant deformation mechanisms to be {10-12} twinning and prismatic slip under compression along the RD and TD and {11-22} twinning and basal slip under compression along the ND. Calculation of twinning strain and analysis of the in-grain lattice rotation angle revealed that the relative contribution of twinning to deformation increased in the order of ND>RD>TD, but that of prismatic slip decreased in the order of ND<RD<TD. These results demonstrate that activations of twinning and slip systems and their relative activities vary significantly with the applied deformation direction owing to the preferred crystallographic orientation of the initial material.</P>