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Non‑associated and Non‑quadratic Characteristics in Plastic Anisotropy of Automotive Lightweight Sheet Metals

Automotive Innovation 2023年第3期6卷 364-378页

作者： Yong Hou Junying Min myoung‑gyu lee Department of Materials Science and Engineering and RIAM Seoul National UniversitySeoul 08826South Korea School of Mechanical Engineering Tongji UniversityShanghai 201804China

Lightweight sheet metals are highly desirable for automotive applications due to their exceptional strength-to-density *** accurate description of the pronounced plastic anisotropy exhibited by these materials in finite element analysis requires advanced plasticity *** recent years,significant efforts have been devoted to developing plasticity models and numeri-cal analysis methods based on the non-associated flow rule(non-AFR).In this work,a newly proposed coupled quadratic and non-quadratic model under non-AFR is utilized to comprehensively investigate the non-associated and non-quadratic characteristics during the yielding of three lightweight sheet metals,i.e.,dual-phase steel DP980,TRIP-assisted steel QP980,and aluminum alloy *** materials are subjected to various proportional loading paths,including uniaxial tensile tests with a 15°increment,uniaxial compressive tests with a 45°increment,in-plane torsion tests,and biaxial tensile tests using laser-deposited arm-strengthened cruciform *** show that the non-AFR approach provides an effective means for accurately modeling the yield behavior,including yield stresses and the direction of plastic strain rates,simultaneously,utilizing two separate functions and a simple calibration *** introduction of the non-quadratic plastic potential reduces the average errors in angle when predicting plastic strain directions by the quadratic plastic potential ***,for DP980,the average error is reduced from 3.1°to 0.9°,for QP980 it is reduced from 6.1°to 3.9°,and for AA5754-O it is reduced from 7.0°to 0.2°.This highlights the importance of considering the non-quadratic characteristic in plasticity modeling,especially for aluminum alloys such as AA5754-O.

关键词： Yield behavior Non-associated flow rule Non-quadratic Lightweight sheet metal

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Characteristics of surface and subsurface of formed thread parts by axial-infeed thread rolling process

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Chinese Journal of Aeronautics 2023年第3期36卷 471-481页

作者： Shuowen ZHANG Dawei ZHANG Shengdun ZHAO Fei JIANG myoung-gyu lee Xi’an Key Laboratory of Intelligent Equipment and Control School of Mechanical EngineeringXi’an Jiaotong UniversityXi’an 710049China Department of Materials Science and Engineering Seoul National University08826 SeoulRepublic of Korea

The thread rolling process has been widely applied to manufacture high-performance thread *** this process,the evolutions of surface and subsurface are frequently introduced,which affect the working performance of manufactured *** this study,an axial-infeed thread rolling process(ATRP)is employed,and the macro-meso surface characteristics under different lubrications and operating conditions are ***,the distributions of microstructure and hardness on the subsurface of formed tooth are analyzed in detail,along with the study of stress state and yield strength *** is found that the MoS_(2)grease is more effective in reducing the surface roughness and defects than the lubrication oil and water-base graphite during the ATRP *** rolling speed improves the quality of surface morphology and can reduce the surface *** the subsurface of bottom and flank,intensive shear stress occurs in a narrow region,resulting in the elongation and refinement of the grains and increasing the low angle grain boundary *** on the grain size and plastic strain,the yield strength is *** maximum yield strength and hardness on the bottom of formed tooth are improved by 41.2% and 39.4%,respectively.

关键词： ATRP Lubrication Surface characteristics Microstructure distribution Hardness improvement Grain size

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Does friction contribute to formability improvement using servo press?

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Friction 2023年第5期11卷 820-835页

作者： Kali PRASAD Aishwary GUPTA Hariharan KRISHNASWAMY Uday CHAKKINGAL Dilip K.BANERJEE myoung-gyu lee Department of Mechanical Engineering Indian Institute of Technology MadrasChennai 600036India Department of Materials Science and Engineering Seoul National UniversitySeoul 08826Republic of Korea Department of Metallurgical and Materials Engineering Indian Institute of Technology MadrasChennai 600036India Material Measurement Laboratory National Institute of Standards and Technology(NIST)Gaithersburg 20899USA

Servo press forming machines are advanced forming systems that are capable of imparting interrupted punch motion,resulting in enhanced room temperature *** exact mechanism of the formability improvement is not yet *** contribution of interrupted motion in the ductility improvement has been studied through stress relaxation phenomena in uniaxial tensile(UT)***,the reason for improved formability observed when employing servo press is complicated due to the additional contribution from frictional *** the present work,an attempt is made to decouple the friction effect on formability improvement *** improved formability is studied using a hole expansion test(HET).The limit of forming during hole expansion is modeled using the Hosford–Coulomb(HC)damage criteria,which is implemented as a user subroutine in a commercial explicit finite element(FE)*** the contribution of stress relaxation is accounted for in the evolution of the damage variable during interrupted ***,the difference between simulation and experimental hole expansion ratio(HER)can be used to decouple the friction effect from the overall formability improvement during hole *** improvement in HER due to stress relaxation and friction effect is *** study showed that the model effectively captures the hole expansion deformation process in both monotonic and interrupted loading *** to stress relaxation,friction effect played a major role during interrupted HET.

关键词： servo press hole expansion test(HET) dual phase steel finite element(FE)analysis Hosford-Coulomb(HC)ductile fracture model

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Texture modification and mechanical properties of AZ31 magnesium alloy sheet subjected to equal channel angular bending

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Journal of Materials Science & Technology 2021年第8期67卷 211-225页

作者： Shuai-Feng Chen Hong-Wu Song Ming Cheng Ce Zheng Shi-Hong Zhang myoung-gyu lee Institute of Metal Research Chinese Academy of SciencesShenyang110016China Department of Materials Science and Engineering&Research Institute of Advanced Materials(RJAM) Seoul National UniversitySeoul08826Republic of Korea University of Chinese Academy of Sciences Beijing100049China

Analysis of the recently proposed equal channel angular bending(ECAB)process is provided on thin hotrolled AZ31 magnesium alloy *** particular,effects of deformation temperature and strain path on the texture evolution and mechanical properties are systematically investigated under single pass ECAB at various temperatures and multi-pass ECAB process that involves changes in strain *** is found that simultaneous activation of multiple twinning types is successfully introduced during ECAB,which results in obvious tilted component of basal *** to the domination of extension twins,weaker basal textures are detected after both single pass ECAB at 150℃and three cross passes ECAB at 200℃.After annealing,the basal texture is further weakened via twin-related recrystallization and the annealed microstructure is featured with mixture of basal and non-basal orientated ***,the effect of grain orientation on the mode of plastic deformation and the roles of grain orientation and grain boundary on the local strain accommodation are coherently *** study reveals that over 60%increase of uniform elongation with marginal reduction of tensile strength less than 5%can be achieved for single pass ECAB at 150℃and three cross passes ECAB at 200℃,which is the result of larger fraction of grains favored with extension twinning and better local strain accommodation.

关键词： Equal channel angular bending Magnesium alloy Thin sheet Texture Grain boundary Mechanical properties

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Enhancing the Robustness of Rib-Groove Filling and Strain Homogeneity in the Isothermal Forging of Titanium Alloy Multi-Rib Components

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Chinese Journal of Mechanical Engineering 2024年第5期 472-499页

作者： Tong Ding Ke Wei Yong Hou Xianjuan Dong Long Huang myoung-gyu lee School of Aeronautical Manufacturing Engineering Nanchang Hangkong University Department of Materials Science and Engineering & RIAM Seoul National University

Isothermal forging stands as an effective technology for the production of large-scale titanium alloy multi-rib components. However, challenges have persisted, including die underfilling and strain concentration due to the complex material flow and heterogeneous deformation within the forging die cavity. While approaches centered on optimized billet designs have mitigated these challenges, uncertainties in process parameters continue to introduce unacceptable variations in forming accuracy and stability. To tackle this issue, this study introduced a multi-objective robust optimization approach for billet design, accounting for the multi-rib eigenstructure and potential uncertainties. The approach includes finite element(FE) modeling for analyzing the die-filling and strain inhomogeneity within the multi-rib eigenstructure. Furthermore, it integrated image acquisition perception and feed back technologies(IAPF) for real-time monitoring of material flow and filling sequences within die rib-grooves, validating the accuracy of the FE modeling. By incorporating dimensional parameters of the billet and uncertainty factors, including friction, draft angle, forming temperature, speed, and deviations in billet and die, quantitative analyses on the rib-groove filling and strain inhomogeneity with fluctuation were conducted. Subsequently, a dual-response surface model was developed for statistical analysis of the cavity filling and strain homogeneity. Finally, the robust optimization was processed using a non-dominated sorting genetic algorithm II(NSGA-II) and validated using the IAPF technologies. The proposed approach enables robust design enhancements for rib-groove filling and strain homogeneity in titanium alloy multi-rib components.

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Mechanical properties of high-strength concrete subjected to high temperature by stressed test

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中国有色金属学会会刊：英文版 2009年第B9期19卷 128-133页

作者： gyu-Yong KIM Young-Sun KIM Tae-gyu lee Division of Architecture Engineering Chun gnam National University

Recently, the effects of high temperature on compressive strength and elastic modulus of high strength concrete were experimentally investigated. The present study is aimed to study the effect of elevated temperatures ranging from 20 ℃ to 700 ℃ on the material mechanical properties of high-strength concrete of 40, 60 and 80 MPa grade. During the strength test, the specimens are subjected to a 25% of ultimate compressive strength at room temperature and sustained during heating, and when the target temperature is reached, the specimens are loaded to failure. The tests were conducted at various temperatures (20-700 ℃) for concretes made with W/B ratios of 46%, 32% and 25%, respectively. The results show that the relative values of compressive strength and elastic modulus decrease with increasing compressive strength grade of specimen.

关键词：高强混凝土高温作用力学性能测试抗压强度温度升高弹性模量强度试验

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Application of an Artificial Neural Network for a Direct Estimation of Atmospheric Instability from a Next-Generation Imager

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Advances in Atmospheric Sciences 2016年第2期33卷 221-232页

作者： Su Jeong lee myoung-Hwan AHN Yeonjin lee Department of Atmospheric Science and Engineering Ewha Women’s University

Atmospheric instability information derived from satellites plays an important role in short-term weather forecasting, especially the forecasting of severe convective storms. For the next generation of weather satellites for Korea＇s multi-purpose geostationary satellite program, a new imaging instrument has been developed. Although this imaging instrument is not de- signed to perform full sounding missions and its capability is limited, its multi-spectral infrared channels provide information on vertical sounding. To take full advantage of the observation data from the much improved spatiotemporal resolution of the imager, the feasibility of an artificial neural network approach for the derivation of the atmospheric instability is investigated. The multi-layer perceptron model with a feed-forward and back-propagation training algorithm shows quite a sensitive re- sponse to the selection of the training dataset and model architecture. Through an extensive performance test with a carefully selected training dataset of 7197 independent profiles, the model architectures are selected to be 12, 5000, and 0.3 for the number of hidden nodes, number of epochs, and learning rate, respectively. The selected model gives a mean absolute error, RMSE, and correlation coefficient of 330 J kg-1, 420 J kg-1, and 0.9, respectively. The feasibility is further demonstrated via application of the model to real observation data from a similar instrument that has comparable observation channels with the planned imager.

关键词： CAPE artificial neural network instability geostationary imager

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Crown Fuel Characteristics and Carbon Emission from Japanese Red Pine Stands Burned by Crown Fire in Mt. Palgong, South Korea

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Journal of Mountain Science 2012年第5期9卷 656-664页

作者： Byungdoo lee myoung Soo WON Yohan lee Myung Bo lee Division of Forest Disaster Management Korea Forest Research Institute College of Forestry Oregon State University

Carbon emissions from forest fires are considered an important factor of ecosystem carbon balance and global climate change. Carbon emissions from Japanese red pine stands （Pinus densiflora S. et Z.） burned by crown fire were estimated at Mt. Palgong in Daegu Metropolitan City, and crown fuel characteristics, including crown bulk density, crown base height, and fuel moisture content of Japanese red pine, were analyzed. Total biomass combusted was calculated by subtracting the biomass of burned stands from that of unburned stands exhibiting similar stand structures and site environments. Ten trees in the unburned area and five trees in the burned area were cut by using direct harvesting techniques to estimate crown layer biomass. All biomass sampled was oven-dried and weighed. The dry weight ratios of stems, branches, and needles were 7o%, 21%, and 9%, respectively. The available fuel load susceptible to combustion during the crown fire spread was equivalent to 55% of the crown layer biomass. The crown bulk density was 0.24 kg/m3 on average. The estimated amount of CO2 was 23,454 kg CO2/ha for the crown layer. These results will be useful for calculating the amount of CO2 emitted from forest fires and for developing a forest carbon model in P. densiflora forests.

关键词： Biomass burning Crown fire Fuelcharacteristics Bulk density Pinus densiflora

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RADIALLY SYMMETRIC SOLUTIONS FOR QUASILINEAR ELLIPTIC EQUATIONS INVOLVING NONHOMOGENEOUS OPERATORS IN AN ORLICZ-SOBOLEV SPACE SETTING

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Acta Mathematica Scientia 2020年第6期40卷 1679-1699页

作者： Jae-myoung KIM Yun-Ho KIM Jongrak lee Department of Mathematics Education Andong National UniversityAndong 36729Republic of Korea Department of Mathematics Education Sangmyung UniversitySeoul 03016Republic of Korea Department of Mathematics Jeju National UniversityJeju 63243Republic of Korea

We investigate the following elliptic equations:⎧⎩⎨−M(∫R Nϕ(|∇u|2)dx)div(ϕ′(|∇u|2)∇u)+|u|α−2 u=λh(x,u),u(x)→0,as|x|→∞,in R N,where N≥2,1 详细信息

We investigate the following elliptic equations:⎧⎩⎨−M(∫R Nϕ(|∇u|2)dx)div(ϕ′(|∇u|2)∇u)+|u|α−2 u=λh(x,u),u(x)→0,as|x|→∞,in R N,where N≥2,1

关键词： radial solution quasilinear elliptic equations variational methods Orlicz-Sobolev spaces

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Rolling Stability Enhancement via Balancing Tail for a Water-running Robot

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Journal of Bionic Engineering 2015年第3期12卷 395-405页

作者： Hyungyu Kim Dong gyu lee TaeWon Seo School of Mechanical Engineering Yeungnam University Gyeongsan 712-749 Republic of Korea

Running on water produces very energy-efficient and fast motion in water environments. Many studies have been performed to develop bio-inspired water-running robots. To achieve good performance, the lifting force is very important for a robot to be able to run on water. The loss of lifting force is associated with the rolling stability of the robot on water. The purpose of this study is to improve the rolling stability of a water-running robot through the periodic motion of a balancing tail. Kinematic analysis was performed to calculate the motions of the legs and the tail, and static analysis was performed to calculate the balancing effect of the tail motion. A numerical model was suggested to determine the dynamic performance of the robotic platform based on kinematic and static results. A simulation based on the numerical model was performed, and the results were compared with empirical data from a robot prototype. The simulation results are in good agreement with the experimental data in terms of rolling stability The lifting force has only a slight effect. The results of this study can be used as a guideline for designing a stable water-running robot.

关键词： water-running robot balancing tail rolling stability lifting force basilisk lizard

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