Preparation and properties of Al-Al2O3 metal ceramics via powder metallurgy methods

Jieguang Song,Xiuqin Wang,Lin Chen,Cailiang Pang,Jia Zhang,Weiguo Shi,Songlin Guo,Xianzhong Wang,Ruihua Wang 한양대학교 세라믹연구소 2018 Journal of Ceramic Processing Research Vol.19 No.1

Metal ceramics are outstanding new engineering materials that offer the advantages of both ceramics and metals. In this study,Al-Al2O3 metal ceramics were prepared through powder metallurgy methods, and the densification and properties of theprepared metal ceramics were investigated to gain insights into the preparation of high-performance cermet materials. Resultsrevealed that as the forming pressure was increased, the relative density of the ceramics increased, whereas their electricalresistivity decreased. The relative density increased with increasing sintering temperature up to 700 oC and decreased beyond700 oC, whereas the electrical resistivity exhibited an opposite trend. The relative density increased with increasing Al content,whereas the electrical resistivity displayed an opposite trend. Under optimal technological parameters of 700 oC sinteringtemperature, < 20MPa forming pressure, and 75 wt% Al content, Al-Al2O3 metal ceramics with a high relative density(97.52%) and a low electrical resistivity (101.34 Ω·m) were successfully prepared.

Computational Studies on Mesh Stiffness of Paralleled Helical Beveloid Gear Pair

Ruihua Sun,Chaosheng Song,Caichao Zhu,Yawen Wang,Xingyu Yang 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.1

Considering the asymmetrical left and right tooth profiles including the transient curve at the tooth root region and the varying thickness along the axial direction due to the cone angle, we build the accurate profile curve model including the transient curve at the tooth root of helical beveloid gear with machining parameters to solve the problem of non-applicability of real digital model. According to the feature of gear shape varying along tooth width direction, we introduced the slicing method and derived its grouping formula. Finally, the efficient and accurate slicing-based mesh stiff ness calculation model of paralleled helical beveloid gears was proposed using potential energy theory. Then, mesh stiff ness was calculated using finite element contact model for comparison and verification. Finally, the impacts of macro geometry parameters including cone angle, normal pressure angle, helix angle, tooth width and addendum coefficient on single and total mesh stiff ness were analyzed. The calculated mesh stiff ness correlates well with the results from FEM with the maximum peak error is 4.8%. Results show that the tooth width shows an obvious incremental impact on average total mesh stiff ness. When the pressure angle, helix angle, cone angle and addendum coefficient increase, the average total mesh stiff ness increases first and then decreases. For the fluctuating value, it increases as the tooth width, helix angle and cone angle increase. However, the pressure angle and addendum coefficient show an opposite impact on the fluctuating value.

Friele Color Matching Model of Digital Rotor Spinning Viscose Mélange Fabric

Ruihua Yang,Kanglei Zhang,Zhuo Wang 한국섬유공학회 2022 Fibers and polymers Vol.23 No.4

Digital rotor spinning involves spinning fibers that have been dope-dyed together with one of several differenthues in a manner that enables the color tuning of the resultant yarn. A small inventory of colored fibers provides access to awide gamut of shades and production of textiles in a variety of colorways. To overcome the issues with the current intelligentcolor matching system for digital rotor spinning viscose melange yarn, in this study, a digital rotor spinning frame was used tospin selected red, yellow, and blue dope-dyed viscose staple fibers into 66 types of melange yarns at a ratio gradient of 10 %. The corresponding yarns were knitted as fabric samples, and then a Datacolor650 spectrophotometer was used to performcolor testing and record the experimental data. The parameter σ of the Friele model was assigned within [0,1]. The optimalvalue of σ was 0.134 when the average color difference of the bi-component melange sample was minimal, which was usedfor the construction of a color matching system based on the Friele model. In addition, this study verifies the obtained optimalvalue of σ using the full-spectrum color matching method. The average error between the predicted ratio and actual ratio ofthe three-component melange sample was 10.21 %, while the predicted average color difference was 0.4561. This indicatesthat the empirical parameters of the Friele model obtained in this study yield a good prediction accuracy of digital rotorspinning viscose melange products.

The Fracture Property of Biodegradated Natural Fiber Reinforced Composites

Renliang Wang,Jun Hee Song,Ruihua Hu,Ho Chel Yoon,Ngakan Putu Gede Suardana,Yon Jig Kim,Jae-kyoo Lim 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3

Biodegradable natural composite is enormously applied in industrial production. The present work is concerned with effect of chemical treatment on the fracture study of natural fiber reinforced PLA. The fibers were from hemp and rice straw contrastively. The elastic modulus and tensile strength of PLA were2300 ㎫ and 32 ㎫ respectively. The chemical treated fibers and non-treated fibers were used as reinforcement to improve the mechanical properties. Chopped fibers, the component of unidirectional fiber composites, were made by hand and deposited together with PLA films layer by layer in the compression mold. The properties of tensile strength and elastic modulus performed stable in 35 wt% natural fiber composites. The rice straw fiber composites performed good stabilities especially in 50 wt% ones. The SEM showed a typical matrix failure in the morphology observation. Both hemp fiber and rice straw fiber presented good properties in their own ways.

Finite-time Issue of Discrete-time Linear Switched Systems With Partial Finite-time Unstable Modes Based on an Inverse Weighted Switching Scheme

Yunpeng Zhan,Ruihua Wang,Shumin Fei 제어·로봇·시스템학회 2024 International Journal of Control, Automation, and Vol.22 No.2

The work proposes a multiple convex Lyapunov function and an inverse weighted switching scheme to investigate the finite-time stability and finite-time boundedness for a class of discrete-time switched linear systems with partial finite-time unstable modes. A multiple convex Lyapunov function is put forth by constructing a convex combination of positive definite matrices, which can relax the restricted conditions of the Lyapunov function and make it carry more decision variables than traditional Lyapunov function methods. Besides, the inverse weighted switching scheme is devised by summing the reciprocal of each dwell time with weighting coefficients, by which tighter dwell time bounds are ensured. On the basis of the new Lyapunov function and switching scheme, the finitetime control for a class of switched linear systems with partial finite-time unstable modes is addressed. Different from other researches that require all subsystems to be controllable, we only require the existence of one controllable subsystem. In the end, two numerical examples and a tunnel diode circuit example are provided to verify the effectiveness of the developed results.

Migration Characteristics and Potential Ecological Environment Evaluation of Metal Elements in Surface Soil

Fei Liu,Zhong Yang,Ruihua Yang,Ruifeng Wang,Jianhai Zhou 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.5

In view of the excessive heavy metals in soil will affect the quality of crops and the personal safety of local residents, in order to analyze and evaluate the migration characteristics and potential ecological risks of heavy metals in soil in the study area, the heavy metal content, pH, regional distribution, correlation, migration characteristics, enrichment state and potential risk in 0 − 1 m soil depth were tested and analyzed. The results show that the distribution of most metal elements is closely related to pH in the soil. The contents of elements As, Cr and Hg in the soil of the study area change in an “L” shape along with the buried depth, that is, the contents of As, Cr and Hg increase generally along with the buried depth of the soil, and the contents of elements Cd and Pb decrease along with the buried depth. By analyzing the enrichment degree of heavy metals and evaluating the ecological risk degree, it can be concluded that only element Hg is moderately enriched in the soil layer of 0 − 0.4 m and Cd is the main ecological risk factor, and the potential ecological risk degree of Yuyao is between slight and moderate ecological risks.

Fabrication of Novel CuO Films with Nanoparticles-Aggregated Sphere-Like Clusters on ITO and Their Nonenzymatic Glucose Sensing Applications

Fang Sun,Hongwei Jiang,Ruihua Zhu,Dan Wang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.2

In this work, novel nanoparticles-aggregated CuO sphere-like clusters were successfully synthesized on indium tin oxide (ITO) glass through a facile two-step procedure consisting of the fabrication of Cu2O films directly grown on ITO surface by electrodeposition, and subsequent calcinations of Cu2O films leading to the formation of CuO films. The morphology and structure of as-synthesized samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the size of nanoparticles constituting sphere-like clusters structure obtained at 200℃ is much smaller than that of obtained at other temperature, which can provide large surface area for catalytic reaction. The CuO/ITO electrode was applied to detect glucose by cyclic voltammetry (CV) and amperometric detection (i - t). It was found that the obtained CuO films modified ITO electrode exhibited a much higher electrocatalytic activity for the oxidation of glucose in an alkaline medium through heat treatment of 200℃. A favorable performance with a high sensitivity of 1841.5544 µA mM-1 cm-2 to glucose ranging from 1.0 x 10-6 M to 5.0 x 10-4 M, a low operating potential of 0.35V versus Ag/AgCl and a fast amperometric response (within 3 s) were achieved on such CuO/ITO electrode. It also showed outstanding long-term stability and good reproducibility. Notably, poisoning by chloride ions and interference from ascorbic acid, uric acid and acetaminophen were negligible. Therefore, the nanoparticles-aggregated CuO sphere-like clusters would be a promising candidate electrode material for the development of nonenzymatic glucose sensors.

Mechanical properties of biodegradable coconut fibre reinforced polylactic acid composite

Kim Yon Jig(김연직),Phan Quoc Thai(판꾹타이),Renliang Wang(왕렌리앙),Jun Yong Choi(최준용),Ruihua Hu(후루이화),Jae Kyoo Lim(임재규) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6

In the recent years, the use of natural fiber as reinforcements in polymer composites for replacing synthetic fiber is rapidly increased. Coconut is growing in some tropical countries such as Vietnam, Thailand, India... especially, it is very cheap and infinite resource. Polylactic acid (PLA) is a biodegradable thermoplastic polymer, which was used extensively in recent years because the biodegradable composites are friendly with environment. This study is concerned with the mechanical properties of coconut fiber (coir) reinforced PLA composite. The coconut fiber reinforced PLA composite was manufactured by heating compression mold with different contents of coconut fiber. The tensile test and bending test will be carried out to verify the mechanical properties of composite and the effect of coconut contents to them.

Sintering densification and properties of Al2O3/Al cermet materials via powder metallurgy method

Jieguang Song,Yue Liu,Cailiang Pang,Jia Zhang,Lin Chen,Xiling Zhang,Songlin Guo,Xianzhong Wang,Ruihua Wang,Aixia Chen 한양대학교 세라믹연구소 2018 Journal of Ceramic Processing Research Vol.19 No.2

Cermet materials are important new engineering materials with combined advantages of ceramics and metals. In this study,Al2O3/Al cermet materials were prepared through powder metallurgy. The effect of sintering technology on the properties ofAl2O3/Al cermet materials was analyzed as basis for preparing high-performance cermet materials. Results showed that whenthe sintering temperature was increased from 700 oC to 1000 oC under holding time for 1 h, the densification degree and hardnessof Al2O3/Al cermet materials decreased and the electric resistivity increased. In the microstructure of Al2O3/Al cermet materials,Al particles were larger and continuously distributed, whereas the Al2O3 particles were smaller and discontinuously distributed. When the holding time was increased under sintering temperature of 700 oC, the densification degree and hardness of Al2O3/Alcermet materials also increased, and the electric resistivity decreased. When 25 wt% Al2O3/Al cermet materials were sintered at700 oC for 3 h, the densification degree was higher, with hardness of 2203 HV and electric resistivity of 0.0159 Ω • m.