Browsing by Author "Hung, CH"

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A mixed lubrication model for computer simulation of extrusion processes
(2000-10-01)
Hsu , TC
;
Li, YM
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
A mixed lubrication/friction model for extrusion process is developed in the present research. The model combines a rigid-plasticity finite element code to simulate the interface condition between the tooling and workpiece in the extrusion operation. The influence of surface roughness on lubricant flow is treated by using the average Reynolds equation. The active lubrication regime and appropriate friction factor were determined from the current local values of interface variables such as mean lubricant film thickness and workpiece and tooling roughness, in addition to the more traditional external variables such as interface pressure, node sliding velocity and strain rate of the workpiece. Numerical results using the coupled code include friction stress and normal pressure under different lubrication conditions are compared with experimental investigation. The discrepancy is very small and the proposed model proved to be very efficient in predicting interface friction condition in the extrusion processes.
A novel low-temperature growth and characterization of single crystal ZnO nanorods
(2003-12-20)
Hung, CH
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
One-dimensional (1D) single crystal ZnO nanorods directly grown on ZnO nanostructured substrates by soft chemical method is proposed. Employing a novel two steps procedure, the ZnO nanorods with a diameter about 45 nm can be successfully grown on substrate in aqueous solution at attractive low temperature in 90 degreesC, permitting large-scale fabrication with a relatively low cost and a potential application in optoelectronic nanodevices. The structures, appearances and optical properties of ZnO nanorods also have been characterized. (C) 2003 Elsevier B.V. All rights reserved.
A study on seamless tube in the planetary rolling process
(2002-02-28)
Shih, CK
;
Hsu, RQ
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
In this paper, the finite element method and the dual-stream functions upper bound method are selected to analyze the tube rolling process with a planetary rolling mill. Three-dimensional elastic-plastic finite element simulations with special emphasis on the determination of the roller profile and realistic contact conditions between the rollers, workpiece and mandrel are used to reveal the deformation characteristics of seamless tube during the rolling process. In addition, the kinematically admissible velocity field of the deforming tube is described in terms of two stream functions so that the velocity components of the deforming tube can be obtained through the upper bound analysis. In both analysis methods, the equation of meshing is used to determine the contact condition between the rollers and the workpiece. The results from both methods with different variables are observed and compared. (C) 2002 Elsevier Science B.V. All rights reserved.
Combinational AE-AF system with fuzzy climbing search servo
(2006-01-01)
Chen, CY
;
Tseng, CY
;
Hung, CH
;
Yin, IC
;
Wang, SJ
This paper presents a combinational system, which can perform the functionalities of Auto Focus (AF) and Auto Exposure (A-E) at the same time in a very efficient manner. At the first step, this system uses a DOG (Difference of Gaussian) filter to measure image's contrast and sharpness simultaneously. Then, a fuzzy logic-based scheme is proposed for the adjustment of focus and exposure. This system can be easily implemented with low hardware complexity.
Combinational AE-AF system with fuzzy climbing search servo - art. no. 60690B
(2006)
Chen, CY
;
Tseng, CY
;
Hung, CH
;
Yin, IC
;
Wang, SJ
This paper presents a combinational system, which can perform the functionalities of Auto Focus (AF) and Auto Exposure (A-E) at the same time in a very efficient manner. At the first step, this system uses a DOG (Difference of Gaussian) filter to measure image's contrast and sharpness simultaneously. Then, a fuzzy logic-based scheme is proposed for the adjustment of focus and exposure. This system can be easily implemented with low hardware complexity.
Effect of side chain alkyl length on the electroluminescence characteristics of carbazole-based light emitting polymers
(2001-09-28)
Chao, CS
;
Whang, WT
;
Hung, CH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Three carbazole-based copolymers with different long side chains were synthesized using the Wittig reaction. These three copolymers and model compound were characterized by nuclear magnetic resonance (NMR) spectroscopy to determine the cis/trans ratio. The cis/ trans ratios decrease with the side chain length due to the variation in the degree of steric hindrance in the Wittig reaction. They affect the electroluminescence (EL) characteristics of the carbazole-based light emitting polymers. As the length of the side chain increases the wavelength of the emitted light increases proportionally whereas a decrease in the threshold voltages, 5.2, 4.8, 2.5 V was observed. However, EL intensity at same applied voltage creases with the length of the side chain. The energy levels of these three copolymers were also investigated to account for the phenomenon.
Effect of surface stabilization of nanoparticles on luminescent characteristics in ZnO/poly(hydroxyethyl methacrylate) nanohybrid films
(2005-01-14)
Hung, CH
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Highly transparent and stable luminescent ZnO/poly(hydroxyethyl methacrylate) nanocomposites have been synthesized via a nanoparticle surface modified method. 3-(Trimethoxysilyl)propyl methacrylate (TPM) was used as the stabilizing agent in a simple, mild sol-gel route to prepare TPM-modified ZnO nanoparticles. The existence of TPM on the nanoparticle surface effectively promotes the stability of colloidal ZnO nanoparticles and the compatibility between the inorganic nanoparticles and the organic matrix in the solid nanohybrid. The resulting ZnO/PHEMA nanocomposites with TPM-modified nanoparticles have better dispersibility and controllable luminescent properties. The characteristics of TPM-modified and unmodified ZnO nanoparticles have been studied by ultraviolet-visible (UV-vis) absorption spectroscopy, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and (1)H NMR spectroscopy.
Effect of the polyimide structure and ZnO concentration on the morphology and characteristics of polyimide/ZnO nanohybrid films
(2005-01-21)
Hsu, SC
;
Whang, WT
;
Hung, CH
;
Chiang, PC
;
Hsiao, KN
A series of polyimide/ZnO nanohybrid films with different ZnO content were prepared from a rigid pyromellitic dianhydride-4,4'-diaminodiphenyl ether (PMDA-ODA) polyimide (PI) and a flexible 3,3,4,4-benzophenonetetracarboxylic acid dianhydride-4,4'-diaminodiphenyl ether (BTDA-ODA) PI with ZnO nanoparticles (3-4 nm). Fourier-transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) depict that the ZnO nanoparticles function as a physical cross-linking agent with PI through hydrogen bonding between the OH on the ZnO nanoparticles and the C=O of the imide groups. ZnO nanoparticles in the rigid PMDA-ODA matrix cause a larger percentage decrease in the coefficient of linear thermal expansion (CTE) than in the flexible BTDA-ODA matrix. The BTDA-ODA/ZnO hybrid films have two transition peaks in dynamic mechanical tan curves, but PMDA-ODA/ZnO hybrid films only have one transition peak. Thermogravimetric analysis reveals that ZnO decreases the thermal degradation temperature (T-d) in both hybrid films, but less so in PMDA-ODA/ZnO films. Trans-mission electron microscopy (TEM) images reveal that the rigid matrix induces larger particle size (30-40 nm) compared to the flexible matrix (10-15 nm).
Experimental and numerical analyses on three-roll planetary rolling process
(2003-12-10)
Shih, CK
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
This study conducts experiments on a planetary three-roll experimental apparatus and uses plasticine as the working material. Certain rolling characteristics were observed and compared with the data from finite element simulation, which include diameter of workpieces after deformation, the pitch length and threaded angle of spiral marks, and the cavity at the leading end of rolled plasticine. The comparison confirms the correctness of the simulation model for PSW. (C) 2003 Elsevier B.V. All rights reserved.
Finite element analysis and optimization of springback reduction: The ''double-bend'' technique
(1996-04-01)
Shu, JS
;
Hung, CH
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
According to the double-bend technique, springback can be reduced if the U-channel is unbent and bent again at a new site. Thus springback is a function of both the forming die gap and the plate opening. The purpose of this research is first to use the finite element method to analyze the relationship between springback and the forming variables, and then to combine an optmization technique with the finite element analysis to find the optimum forming parameters to reduce the springback. The solutions are compared with experimental data in the literature.
Finite element analysis and optimization on springback reduction
(1999-03-01)
Chou, IN
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
Several springback reduction techniques used in the U-channel bending processes were analyzed with the finite element method, which included are bottoming, pinching die, spanking and movement techniques. The relationship between the amount of springback and the forming parameters in each technique was first established through finite element simulations, and then the optimization analysis was coupled with the finite element analysis to find the optimum forming parameters for each springback reduction technique. (C) 1998 Elsevier Science Ltd. All rights reserved.
Integration of finite element analysis and optimum design on gear systems
(2002-01-01)
Li, CH
;
Chiou, HS
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Hung, CH
;
Chang, YY
;
Yen, CC
This work establishes a batch module called "integration of finite element analysis and optimum design" by taking gear systems as testing examples. This batch module consists of I-DEAS, ABAQUS/Standard and MOST software, which serve as the preprocessor, the numerical solver and the optimizer, respectively. A simple and practical method was developed, by which this module was enabled to search for contact nodes and elements and to automatically define the contact surfaces for contact analysis. A simple gear-pair system and a complete planetary gear system were successively used as testing examples for this integrated module. The module will automatically construct the geometrical model, analyze contact stress and solve for the optimal solutions when gearing parameters are input. The results are expected to enhance the technology of gear system design. (C) 2002 Elsevier Science B.V. All rights reserved.
Low-temperature solution approach toward highly aligned ZnO nanotip arrays
(2004-07-15)
Hung, CH
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Highly aligned and free-standing ZnO nanotip arrays grown on the ZnO films by soft chemical method are proposed. X-ray diffraction analysis shows that the ZnO nanotips are hexagonal wurtzite structure, and the c-axes of nanotips are perfectly along the substrate surface normal. HRTEM demonstrates the ZnO nanotip to be a single crystal. Room temperature photoluminescence of the ZnO nanotips has a strong UV emission band at 378 nm. The field emission of ZnO nanotip arrays shows a turn-on field of about 10.8 V/mum at a current density of 0.1 muA/cm and emission current density up to about 1 mA/cm(2) at a bias field of 19.5 V/mum. The mild technique for fabricating ZnO nanotip arrays is believed to open novel possibilities for nanoscale optoelectronic device applications. (C) 2004 Elsevier B.V. All rights reserved.
Temperature and thermal deformation analysis on scrolls of scroll compressor
(2005-08-01)
Lin, CC
;
Chang, YC
;
Liang, KY
;
Hung, CH
;
機械工程學系
The thermal deformation of scrolls significantly affects the hermetic property between scrolls, and thus affects the efficiency of the scroll compressor. An accurate temperature distribution on scrolls must be obtained before the thermal deformation of scrolls can be analyzed. The temperature inside real scrolls in the steady state was experimentally measured. Then, reasonable thermal boundary conditions were applied to perform a heat transfer analysis to determine the temperature distribution on scrolls. Then, the distribution of the thermal deformation on scrolls was analyzed. Finally, fixed and orbiting scrolls were engaged with each other and analyses were performed to determine the stress and deformation distributions at the orbital angle that the maximum compression ratio happens. (c) 2004 Elsevier Ltd. All rights reserved.
The computer simulation of lubricated cold rolling processes
(2001-04-01)
Hsu, TC
;
Wu, HM
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
A realistic friction model for lubricated cold rolling process with front and back tension is developed. The model combines a rigid-plasticity finite element code with a lubrication analysis. The rolls al-e assumed to be rigid and uniform deformation and isothermal conditions al e assumed to prevail. The surface roughness effect an lubricant flow is included by using a average Reynolds equation. The active lubrication regime and appropriate friction factor can then be expressed in terms of internal interface variables in addition to the more traditional external variables. These internal variables include mean lubricant film thickness, workpiece roughness and roll roughness. The external variables are interface pressure and sliding speed. Numerical results using the coupled code such as roll separating force and roll torque under different rolling conditions are compared with experimental investigation. The simulation results are in good agreement with experimental data.
The design and development of a hydrostatic extrusion apparatus
(2000-08-31)
Hung, JC
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Hung, CH
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機械工程學系
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Department of Mechanical Engineering
The purpose of this research is to design and construct an experimental hydrostatic extrusion apparatus which has a maximum working pressure of 10 000 kg/cm(2). and to reduce the cost of this extrusion apparatus. The high-pressure extrusion container has been designed with two-layer pyramidal cylinders, and the material used was SKD61 which is cheap and readily available. Different materials and designs for high-pressure seals were tested and analyzed for the best combination performance. Problems in the extrusion processes using this device a ere analyzed and solved, which increased the reliability of the device. The results of extrusion experiments have established that this device is practicable, (C) 2000 Published by Elsevier Science S.A.
The finite element analysis on planetary rolling process
(2001-06-15)
Shih, CK
;
Hung, CH
;
Hsu, RQ
;
機械工程學系
;
Department of Mechanical Engineering
This paper is focused on using the finite element method to simulate and analyze the planetary rolling process. First, a basic geometric model of the planetary rolling mill that considers roll profiles and offset angle of the rolls was constructed. Then, a three-dimensional elastic-plastic finite element simulation was used to analyze both the deformation characteristics of this process and the distributions of stress and strain in the workpieces. During simulations, an algorithm called Equation of Meshing was proposed by which the initial contact conditions between the rollers and the workpiece were successfully derived. Finally, an optimum design method was integrated into this analysis for seeking the best design variables in order to reduce the cavity conditions in the leading end of milled steel rods. (C) 2001 Elsevier Science B.V. All rights reserved.
The finite-element study on extrusion of powder/solid composite clad rods
(1999-11-01)
Chou, IN
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
This paper is concerned with the extrusion process of powder/metal composite clad rods. In this study, the finite-element model established in previous work was used to analyze the effects of various forming parameters, which included the extrusion ratio, the semi-die angle, the radius of the core and the material of the sleeve in extrusion processes. The finite-element results gave the consolidation condition, the stability of the powdered core and the maximum extrusion load for various forming parameters. Experiments were carried out, the results being in good agreement with the finite-element predictions. From the results of analysis, the effects of each forming parameter were determined. (C) 1999 Elsevier Science S.A. All rights reserved.
The influence of ultrasonic-vibration on hot upsetting of aluminum alloy
(2005-08-01)
Hung, JC
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
The traditional ultrasonic apparatus cannot be operated at high temperature, explaining why the effect of ultrasonic-vibration on high temperature metal forming has seldom been addressed in literature. This study establishes an ultrasonic-vibration hot upsetting system. A cooling mechanism is used to solve the problem of high temperature. The effects of temperature and strain rate during ultrasonic-vibration on the upsetting of aluminum alloy were explored using this new system. Experimental results indicate that ultrasonic-vibration can considerably reduces the compressive forces during hot upsetting. The reducing effect on compressive forces decreases while the temperature increases. The strain rate does not significantly affect the reducing effect on compressive forces. (c) 2005 Elsevier B.V. All rights reserved.
Three-dimensional finite element analysis of sheet-metal bending with complex die geometry
(1997-08-01)
Chou, IN
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
The purpose of this research was to and manufacturing processing conditions that would prevent the occurrence of fractures in a sheet-metal bending product. The finite element code ABAQUS was used to analyze the tensile strain at the particular point where fractures frequently occur. First an optimal combination of factors was sought using the method of controlling parameters. The analysis showed that the three factors, r(2), r(4), and the coefficient of friction, which are typical controlling factors, cannot be used to reduce the tensile strain at the critical point efficiently. A preform design was then applied to solve the problem of fracturing. By using a two-step bending operation, we successfully moved the highest tensile strain away from the critical point and also reduced the magnitude of this strain.