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Flow Behaviour and Constitutive Modelling of a Ferritic Stainless Steel at Elevated Temperatures
Jingwei Zhao,Zhengyi Jiang,Guoqing Zu,Wei Du,Xin Zhang,Laizhu Jiang 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.3
The flow behaviour of a ferritic stainless steel (FSS) was investigated by a Gleeble 3500 thermal-mechanical test simulator over the temperature range of 900-1100 °C and strain rate range of 1-50 s -1 . Empirical and phenomenological constitutive models were established, and a comparative study was made on the predictability of them. The results indicate that the flow stress decreases with increasing the temperature and decreasing the strain rate. High strain rate may cause a drop in flow stress after a peak value due to the adiabatic heating. The Zener-Hollomon parameter depends linearly on the flow stress, and decreases with raising the temperature and reducing the strain rate. Significant deviations occur in the prediction of flow stress by the Johnson-Cook (JC) model, indicating that the JC model cannot accurately track the flow behaviour of the FSS during hot deformation. Both the multiple-linear and the Arrhenius-type models can track the flow behaviour very well under the whole hot working conditions, and have much higher accuracy in predicting the flow behaviour than that of the JC model. The multiple-linear model is recommended in the current work due to its simpler structure and less time needed for solving the equations relative to the Arrhenius-type model.
The evaluation of cellular immune function in elderly patients with systemic lupus erythematosus
Kun Men,Yu Chen,Jingwei Zhang,Dianjun Wei 대한내과학회 2019 The Korean Journal of Internal Medicine Vol.34 No.4
Background/Aims: To evaluate cellular immune function in systemic lupus erythematosus (SLE) patients over 60 years old, the association between antinuclear antibody (ANA) titers and the ratio of CD4+/CD8+ was analyzed in this study. The distribution of ANAs and extractable nuclear antibodies (ENAs) in a healthy elderly population was also investigated. Methods: Serum ANA titers were assayed by indirect immunofluorescence (IIF) and the CD4+/CD8+ T-cell ratio was determined by flow cytometry in 76 SLE patients and 30 healthy control individuals. IIF of cytoplasm and nuclear and nucleolar staining were performed on samples taken from 286 healthy elderly individuals. ENA levels were determined using a strip enzyme immunoassay among patients that tested positive for ANAs. Results: ANA titers were negative in the 30 control individuals, but were positive in the 76 SLE patients. Based on ANA titers, the SLE patients were stratified to low (≤ 1:320), medium (1:640 to 1:1,280), and high (≥ 1:2,560) titer groups. The average CD4+/CD8+ ratio of the SLE group was significantly lower than that of the control group. Among the 286 healthy elderly volunteers, 59 (20.63%) tested positive for ANAs. A homogeneous pattern was present in 47.46% of those 59 patients and a granule pattern in the karyoplasm was present in 33.90%. Furthermore, of the 59 patients, ENAs immunoassay was positive in 18 (30.51%); Sjogren syndrome-related antigen A (SSA)/52 kd and Sjogren syndrome antigen B (SSB)/La were the two major antibodies. Conclusions: The significantly lower CD4+/CD8+ ratio among SLE patients over 60 years old is associated with deregulated immune responses and the development of SLE. A low ANA titer (1:160) is common in healthy elders, emphasizing the importance of considering age when determining if the evaluation of ANA titers is to be included in autoimmune disease diagnosis.
High Temperature Oxidation Behaviour of Ferritic Stainless Steel SUS 430 in Humid Air
Xiawei Cheng,Zhengyi Jiang,Dongbin Wei,Jingwei Zhao,Brian J. Monaghan,Raymond J. Longbottom,Laizhu Jiang 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.2
The high temperature oxidation behaviour of ferritic stainless steel SUS 430 was investigated over the temperaturerange from 1000 to 1150 °C in humid air containing 18% water vapour. Isothermal thermogravimetricanalyses were performed to study the oxidation kinetics. The microstructure, composition and thickness ofthe oxide scale formed were investigated via optical microscopy (OM), X-ray diffraction and a scanning electronmicroscope equipped with an energy dispersive spectrometer. The results indicate that breakaway oxidationoccurs at all temperatures and that its onset is accelerated by increasing temperature. The growth rate of themultilayer oxide scale follows a parabolic law with apparent activation energy of 240.69 kJ/mol, and theformation of FeO is decreased when the temperature is higher than 1120°C. The inner oxide scale, Fe-Cr spinel,grows mainly inward and internal oxidation is observed even in a short oxidation test at 1150°C for 105 s. The mechanism of high temperature oxidation of SUS 430 in humid air containing 18% water vapour is discussed.
Localized Surface Plasmon Resonance Properties of Concentric Dual-Ring Nanodisk
Haiwei Mu,Jianxin Wang,Qiang Liu,Wei Liu,Xianli Li,Jingwei Lv,Chao Liu,Famei Wang,Tao Sun,Paul K. Chu 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2019 NANO Vol.14 No.6
The extinction spectral properties based on localized surface plasmon resonance (LSPR) of the concentric dual-ring nanodisk (CDRN) structure are investigated by discrete dipole approximation (DDA) and plasmon hybridization theory. The CDRN nanostructure shows flexible tunable multipole resonances in the near-infrared regime and the coupled resonance wavelengths depend on the structural parameters of the nanostructure, which has great potential in multichannel LSPR-based bio-sensing applications.
김동호,조일현,송동길,Hua Zheng,Li, Jingwei,Zhu, Jiawen,Huang, Xing,Yan, Wei,Xu, Zhen 서울대학교 교육연구소 2021 Asia Pacific Education Review Vol.22 No.2
The self-paced nature of asynchronous online learning (AOL) is recognized as an obstacle that disrupts student success in the learning environment. Without on-time interventions provided by instructors, students find it challenging to use learning strategies tailored to the learning environment, and their use of self-regulated learning (SRL) strategies has been regarded one of the key indicators of success in AOL. To examine how student SRL strategies are associated with their video engagement trajectory and learning outcomes, we used student video engagement data collected at multiple time points. Participants were 159 students who were taking a self-paced asynchronous online statistics course. Results revealed that student video engagement was found to increase over time and student management strategies contributed to the upward change. We also found that the growth of engagement predicted student achievement in the course. Our findings shed light on instructional strategies to support students in AOL contexts.
Effect of Temperature and Strain Rate on the Hot Deformation Behaviour of Ferritic Stainless Steel
Guoqing Zu,Yukuan Lu,Yi Yan,Xiaoming Zhang,Jingwei Zhao,Wei Du,Xu Ran,Zhengyi Jiang 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.2
The fow behaviour and microstructure characteristics of a ferritic stainless steel were investigated using plain strain compression test on a Gleeble 3500 thermo-mechanical test simulator with a hydrawedge system in the temperature range of850–1100 °C and strain rate range of 0.1–50 s−1. The phenomenological constitutive model and the relationship betweenthe Zener–Hollomon (Z) parameter and fow stress were established. The results reveal that the fow softening phenomenonoccurs at high strain rate, which is caused by the coupling efect of the adiabatic heating and dynamic recrystallisation (DRX). New grains nucleate preferentially at the original grain boundaries by strain-induced grain boundary migration. With anincrease of temperature or strain rate, a part of new grains form in the interior of deformed grains. The DRX grain size andfraction increase with the increase of temperature, however, exhibit a non-linear relationship with strain rate.
A Study on Optimum Design Method of Gear Transmission System for Wind Turbine
Jing Wei,Cheng Lv,Wei Sun,Xiang Liu,Yang Wang 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.
As the key components of wind turbine, the weight of gear transmission system becomes larger and larger with the increasing power of wind turbine. Lightweight and high reliability has been the developing tendency for planetary gear transmission system for working reliability and reducing costs. A coupled nonlinear dynamics modeling for planetary gear transmission system in wind turbine is established after comprehensive considering these non-linear factors associated with time-varying mesh stiffness, dynamic transmission error, gear mesh impact and input varying load. Load factors of planetary gear transmission system are induced from the coupled nonlinear dynamics modeling. Then a novel optimum design approach including lightweight and reliability as constraints is presented. The optimization results show that the reliability of original parameters is higher than that of the optimized parameters,while the volume of planetary gear transmission system can greatly be decreased with the overall system reliability requirements.
Effects of dynamic transmission errors and vibration stability in helical gears
Jing Wei,Pan Gao,Xinglong Hu,Wei Sun,Jing Zeng 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.6
Transmission error is an important reason for instability in helical gears. A six-degree-of-freedom dynamic model coupled flexional,torsional and axial motion of a helical gear transmission system, which includes time varying mesh stiffness, bearing supporting stiffness,mesh damping and backlash, is developed, after taking into account the dynamic characteristics and vibration responses of helical gear inthree dimensions. Influences of involute contact ratio, bearing supporting stiffness, mesh damping and backlash on the dynamic transmissionerrors and vibration stability of the helical gear system are investigated using numerical simulation technique. The effects on dynamictransmission errors and stabilities by contact ratio, supporting stiffness and mesh damping as well as gear backlash are analyzed. The intrinsic relationship between above parameters and dynamic transmission errors and stabilities for helical gear system are presented. The stable and unstable regions under different parameters are given. The results in this paper can be helpful to the dynamic and stabledesign of a helical gear transmission system.