Dynamics modeling and modal experimental study of high speed motorized spindle

Yunsong Li,Xiaoan Chen,Peng Zhang,Jinming Zhou 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.3

This paper presents a dynamical model of high speed motorized spindles in free state and work state. In the free state, the housing is modeled as a rotor with equivalent masses including bearing pedestals, motor stator and rear end cover. As a consequence, a double rotor dynamics can be modeled for high speed motorized spindles by a bearing element which connects the housing and bearing pedestals. In the work state, the housing is fixed and the system becomes a bearing-rotor dynamical model. An excitation-measurement test in the free state is designed to analyze the cross spectral density and auto spectral density of input and output signals. Then the frequency response function of system and coherence function of input and output signals which are used to analyze the inherent characteristics of the double-rotor model can be obtained. The other vibration test in the work state is designed to research the dynamical supporting characteristics of bearings and the effects from bearings on the inherent characteristics of the system. The good agreement between the experimental data and theoretical results indicates that the dynamical model in two states is capable of accurately predicting the dynamic behavior of high speed motorized spindles.

Performance of Microtextured Tools Fabricated by Inductively Coupled Plasma Etching in Dry Cutting Tests on Medium Carbon Steel Workpieces

Yunsong Lian,Huifeng Chen,Chenliang Mu 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.2

Microtextures were successfully fabricated on the rake face of the cemented carbide (WC/TiC/Co) tools through inductively coupled plasma etching technology. Two types of microtextured tools were designed and fabricated. Their performance in cutting the AISI 1045 medium carbon steel was tested and compared to that of conventional non-textured tools. The comparison involved cutting forces, cutting temperature, friction coefficient, tool wear, chip adhesion, and machined workpiece surface roughness. The results show that microtextures on the rake face of the cutting tool can make the cutting process more stable than a conventional non-textured tool, and different textures may be suitable for different ranges of the cutting speed. In the latter range 100–200 m/min, microtextures significantly reduce the cutting force, cutting temperature, friction coefficient at the tool–chip interface, while the anti-adhesion property of textured tools and the surface quality of machined workpieces attain their maximal values. The effectiveness of textures is shown to be affected by chip adhesion and blockage resulting from derivative cutting, which appears at high cutting speeds. Moreover, the violation of the structural integrity of textures and their damage can strongly deteriorate the cutting process at low cutting speeds.

Experimental Investigation and Mechanism Analysis of Tungsten Disulfide Soft Coated Micro-Nano Textured Self-Lubricating Dry Cutting Tools

Yunsong Lian,Huifeng Chen,Chenliang Mu,Jianxin Deng,Shuting Lei 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.5 No.2

A new dry cutting tool named WS2 soft coated Micro-Nano textured self-lubricating dry cutting tool (WTT tool) is developed and tested. Dry turning tests have been carried out on 45# quenched and tempered steel with a WTT tool and three other types of alternative tools. The machining performance was assessed in terms of the cutting forces, cutting temperature, friction coefficient at the tool-chip interface, chip deformation, tool wear, and the surface roughness of the machined workpiece. The results show that the WTT tool has the best cutting performance among all the tools tested under the same cutting conditions. Through theoretical analysis and experimental results, the mechanisms of the WTT tool in improving cutting performance were put forward. Meanwhile, the effect of Micro-Nano texture and WS2 soft coating on the cutting forces and the cutting temperature is analyzed. It can be concluded that the WTT tool can effectively improve the anti-adhesion and wear-resistance properties and increase the tool life.

Output decoupling modeling of a XY flexure-based compliant manipulator

Yunsong Du,Tie-Min Li 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.1

This paper presents the coupling stiffness modeling of an XY flexure-based manipulator. Stiffness/compliance equations for compliant mechanisms are first obtained. According to a simplified spring model, the input stiffness and coupling stiffness of the proposed manipulator consisting of outer and inner kinematic chains are then derived. This simplified spring model is composed of four parallel chains, such as the left, lower, upper and right parallel chain. Subsequently, the external force/moment and the output displacement of the manipulator are analyzed by using finite element analysis (FEA). Finally, a prototype of the manipulator is fabricated. Its motion range and the corresponding cross-coupling displacements are measured, and thus the cross-coupling ratios can be derived. It demonstrates that the manipulator possesses good decoupling characteristic, and the proposed theoretical model is reasonable and accurate.

Dynamic analysis of a flexure-based compliant stage

Yunsong Du,Tie-Min Li,Guohua Gao 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.11

This paper presents the dynamic analysis of a flexure-based compliant stage. The dynamic model is first obtained, after which the equivalent masses of the flexure hinge, including the axial equivalent mass, the bending equivalent mass, and the shear equivalent mass, are derived. According to this method, the equivalent mass components of the proposed stage are derived by accumulating those of the output platform, input platform, and flexure hinges. Finally, to verify the validity of the proposed method, the first two resonant frequencies and the corresponding mode shapes are analyzed by using finite element analysis (FEA). An experimental platform is fabricated, and experimental results and FEA values appear to be in accordance with the theoretical calculations. This result demonstrates that the dynamic model and equivalent mass are accurate. The dynamic model provides an effective method for calculating equivalent masses, and dynamic characteristics can be precisely estimated from the corresponding analytical models.

H₂O Adsorption/Desorption in MOF-74: <i>Ab Initio</i> Molecular Dynamics and Experiments

Li, Yunsong,Wang, Xinjiang,Xu, Dongyan,Chung, Jae Dong,Kaviany, Massoud,Huang, Baoling American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.23

<P>Using density functional theory based molecular dynamics with the tight-binding approximation and experimental characterization, the H<SUB>2</SUB>O vapor adsorption/desorption processes in Zn-MOF-74 and the corresponding influence on the lattice dynamics were investigated. It was found that the Zn sites are preferred for H<SUB>2</SUB>O adsorption, and they even allow for the adsorption of multiple H<SUB>2</SUB>O molecules on the same site, making it possible to form stable H<SUB>2</SUB>O cluster at low temperatures. The adsorption heats of different adsorption processes were predicted, and the possibility of H<SUB>2</SUB>O cluster formation under vapor exposure at low and room temperatures was explored. The first adsorbed H<SUB>2</SUB>O can only be dissociated at elevated temperatures, therefore reducing the cyclic uptake near the room temperature. The vibrational spectra of the lattice and adsorbed H<SUB>2</SUB>O were also calculated using molecular dynamics simulation to illuminate the variation of lattice dynamics during the adsorption. The framework was found to be stable after water vapor exposure near room temperature but may start to collapse at around 570 K. X-ray diffraction and H<SUB>2</SUB>O adsorption isotherm measurements have been conducted to verify the theoretical predictions, and good agreements are found.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-23/acs.jpcc.5b02069/production/images/medium/jp-2015-02069m_0008.gif'></P>

Helium Bubble Formation in Neutron Absorber Material Irradiated in Spent Nuclear Fuel Pool

Jung, Yunsong,Kim, Kiyoung,Ahn, Sangjoon AMERICAN NUCLEAR SOCIETY 2018 Transactions of the American Nuclear Society Vol.119 No.-

Populist Terrorist Activities and their Impact in Pakistan

Bo Tu,Bingfeng Fu,Yunsong Zhou,Daitong Liang 한국정치사회연구소 2020 한국과 국제사회 Vol.4 No.1

In Pakistan, there are various types of populist organizations, among which some extreme populist organizations such as those in Baluchistan, Sindh, Gilgit and other regions have become extreme and taken on a certain terrorist nature because of Pakistan s history and politics as well as the long tradition of Pakistan s domestic terrorism. These extremist populist organizations have not only posed a threat to Pakistan s national security and development, but also hindered the strengthening of both China-Pakistan bilateral relations and the cooperation around the Belt and Road Initiative. The specific organizational structure of these extreme populist groups and the impact of their terrorist activities on both Pakistan and the rest of the world deserve attention in the academic community. By adopting a literature review approach, in this paper, Pakistan’s domestic populist organizations are sorted reasonably, the structure of extreme populist organizations is clarified accordingly, and the influence of their terrorist activities is noted emphatically. The conclusion drawn is that Pakistan’s domestic extreme populist groups have not only severely constrained Pakistan’s economic development and lowered the people’s living standards, but also hindered the strengthening of Pakistan’s diplomatic relations with neighboring countries, thus worsening Pakistan’s domestic political environment and impeding its integration into the trend of globalization. 파키스탄의 포퓰리즘 조직은 몇 가지 유형으로 나눌 수 있다, 그 중에 극단적 포퓰리즘 조직의 예를 들면 발루치스탄(Baluchistan), 신드(Sindh), 길기트(Gilgit) 등 지역의 포퓰리즘조직은 역사적, 정치적 원인으로 테러리즘 성질을 가지고 있다. 이러한 극단적 포퓰리즘 조직들은 파키스탄의 국가 안보 및 발전에 영향을 줄 뿐만 아니라 중-파 양국관계 및 “일대일로”를 중심으로 한 협력에도 영향을 준다. 이 조직들이 어떻게 형성되었는지, 어떤 특징을 갖고 있는지를 연구하고 구체적으로 파키스탄 및 국제사회에 어떠한 영향을 미치는가가 학계의 관심사이다. 본 논문은 문헌연구를 통해 파키스탄의 포퓰리즘조직을 분류하고, 조직구성 및 그들의 테러리즘활동이 미치는 영향을 연구하였다. 극단적 포퓰리즘조직들은 파키스탄의 국내정치환경을 악화시키고 본국의 국제화를 지연시킨다. 이와 더불어 파키스탄의 경제성장발전과 국민생활 수준의 향상을 저해시키고 있다. 또한 주변국가간의 외교관계도 악화시키고 있다는 점도 도출하였다.

솔레노이드 밸브의 신뢰성 향상을 고려한 제어 시스템 개발

황순철(Suncheol Hwang),남윤송(Yunsong Nam),오상응(Sangeung Oh),정재훈(Jaehoon Jung),이종철(Jongcheol Lee) 한국항공우주학회 2022 한국항공우주학회 학술발표회 논문집 Vol.2022 No.11

Fabrication and thermal conductivity of CeO₂-Ce₃Si₂ composite

Ahn, Jungsu,Kim, Gyeonghun,Jung, Yunsong,Ahn, Sangjoon Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.2

Various compositions of CeO₂-Ce₃Si₂ (0, 10, 30, 50, and 100 wt%Ce₃Si₂) composites were fabricated using conventional sintering and spark plasma sintering. Lower relative density, enhanced interdiffusion of oxygen and silicon, and silicide agglomerations from the congruent melting of Ce₃Si₂ at 1390 ℃ were only observed from conventionally-sintered pellets. Thermal conductivity of spark plasma sintered CeO₂-Ce₃Si₂ composites was calculated from the measured thermal diffusivity, specific heat, and density, which exhibited dense (>90 %TD) and homogeneous microstructure. The composite with 50 wt%Ce₃Si₂ exhibited 55% higher thermal conductivity than CeO₂ at 500 ℃, and 81% higher at 1000 ℃.