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- 저자 : Daw (검색결과 46 건)
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Springback prediction of the vee bending process for high-strength steel sheets
Daw-Kwei Leu,Zhi-Wei Zhuang 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.3
The precise prediction of springback is a key to assessing the accuracy of part geometry in sheet bending. A simplified approach is developed by considering the thickness ratio, normal anisotropy, and the strain-hardening exponent to estimate the springback of vee bending based on elementary bending theory. Accordingly, a series of experiments is performed to verify the numerical simulation. The calculation of the springback angle agrees well with the experiment, which reflects the reliability of the proposed model. The effects of process parameters such as punch radius, material strength, and sheet thickness on the springback angle are experimentally tested to determine the dominant parameters for reducing the springback angle in the sheet bending process for high-strength steel sheets. Moreover, the effects of the thickness ratio, normal anisotropy, and the strain-hardening exponent on the springback angle in the vee bending process for high-strength steel sheets are theoretically studied. Therefore, improving understanding on and control of the springback reduction of the vee bending process in practical applications is possible.
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Controlling the Properties of OPEFB/PLA Polymer Composite by Using Fe2O3 for Microwave Applications
Daw Mohammad Abdalhadi,Zulkifly Abbas,Ahmad Fahad Ahmad,Khamirul Amin Matori,Fahmiruddin Esa 한국섬유공학회 2018 Fibers and polymers Vol.19 No.7
Microwave-absorptive polymer composite materials provide protection against interference to communication systems caused by microwave-inducing devices. Microwave-absorptive polymer composites were prepared from polylactic acid (PLA) biocomposite blended with oil palm empty fruit bunch (OPEFB) fiber and commercial Iron oxide (Fe2O3) as filler using the melt-blending method. The composites characterization was carried out using the scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The coefficient of reflection S11 and coefficient of transmission S21 of the composites for various Fe2O3 filler percentages were determined using a rectangular waveguide in connection with microwave vector network analyser (HP/Agilent model PNA N5227). These coefficients were then used to calculate microwave-absorption properties (in decibels). XRD analysis showed that increasing amounts of reinforced material (Fe2O3) reduces the crystallinity of the composites. SEM data indicated that Fe2O3 filler ratio increased in the composites, and adhesion to the cellulose fiber grew gradually until the highest percentage of filler was added. The complex relative permittivity and relative permeability were obtained within the broad frequency range of 8-12 GHz at room temperature for various percentages of filler and were measured by the transmission/reflection method using a vector network analyser. Fe2O3 embedment in OPEFB/PLA was observed to have resulted in enhancing the dielectric and magnetic properties. The values of permittivity and permeability increased with increasing Fe2O3 filler content. Theoretical simulation studied the relation between ε' and ε" of the relative complex permittivity in terms of Cole-Cole dispersion law. The result indicated that the processes of Debye relaxation in Fe2O3/OPEFB/PLA, the unique dielectric characteristics of Fe2O3 cannot be accounted for by both the Debye dipolar relaxation and natural resonance. Results further showed that the material transmission, reflection, and absorption properties could be controlled by changing the percentage of Fe2O3 filler in the composites.
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Daw-Kwei Leu 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.6
This work presents an indentation model of the Brinell hardness test, which is a rigid ball-deformable plane contact model (RB-DP model), to elucidate the sliding friction mechanism of sheet metal forming. In the proposed model, the friction force can be defined as a combination of shear (shearing effect) and plough (ploughing effect) forces. The real contact area ratio α is determined from the RBDP model under sliding condition. Moreover, the lateral contact area ratio / A_c A_r can be specified as a function of the real contact area ratio α . Based on Meyer’s law and Hertz contact problem, the maximum contact area ratio α_u , a limiting condition of the real contact area ratio α , can be described as a function of the strain hardening exponent n. Additionally, a limiting condition applies: the strain hardening exponent n must be less than 0.64 in the present model. The present friction model reveals that the friction coefficient μ_d is a function of strain hardening exponent n, the real contact area ratio α and the maximum contact area ratio α_u . The calculated friction coefficient μ_d agrees with the published experimental results.
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Daw Debottam,Sebait Riya,Biswas Chandan 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.10
Rotationally aligned, two-dimensional (2D), transition-metal dichalcogenides (TMDs) exhibit unique electronic, optical, and optoelectronic properties compared to random stacking. Rotationally aligned graphene stacking was demonstrated previously for numerous exotic phenomena, such as superconductivity, resonant tunneling, and moiré pattern. However, rotationally aligned dry-transfer techniques of TMDs, have yet to be demonstrated. Here, we show a simple method of selective cutting of a few-layer tungsten diselenide (WSe2) flake and rotationally aligning it by using dry-transfer stacking. The dry transfer techniques used for this study were adapted to maintain low sample contamination, a high-quality interface, a low number of defects. A combination of viscoelastic and thermoelastic materials was used for the TMD pickup and release to facilitate the rotationally aligned stacking. Aligned WSe2 stacks were characterized by Raman and photoluminescence spectroscopy to evaluate the integrity of the fabricated stack. This study highlights the possibility of using a rotationally aligned, artificial stacking method for exfoliated TMD materials for future electronic and optoelectronic applications.
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Daw-Kwei Leu 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.1
In this study, a series of experiments are performed to characterize the asymmetric V-die bending process for a High-strength steel(HSS) sheet. The main challenge in asymmetric V-die bending is positional deviation of the bending point during bending, given by amagnitude and a direction of deviation of the bending point. The effects of process parameters, such as radii of the punch head and thedie shoulder, on the positional deviation of the bending point were experimentally examined to identify those that govern the deviation ofthe bending point in an asymmetric bending process. This work improves our understanding of deviations of the bending point, and canbe used for developing process design guidelines for asymmetric bending of high-strength steel sheets to produce precise, asymmetricallybent parts.
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Daw-Kwei Leu 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.8
This work evaluates the friction coefficient using the model of plastic hemispherical contact against a rigid flat. The fractional profile of an ellipsoid is utilized to describe the deformed hemispherical shape, and simultaneously define the contact area ratio. Particularly, an adhesion factor is defined to assess the junction ability of asperity adhesion under compressive loading. Additionally, the complex process of contact is assumed as a series of contact states changing from fracture to shearing. The friction coefficient, which obeys the constant friction law, is then derived as a function of interference and strain hardening exponent via adhesion theory. Finally, a comparison of friction coefficient is made with the published experiment, showing that the calculated value is larger than the experimental value. Some practical conclusions are presented and a conceptual understanding of contact friction is provided.
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Daw-Tung Lin,Kuan-Yu Wu 보안공학연구지원센터 2016 International Journal of Multimedia and Ubiquitous Vol.11 No.3
Seamless object tracking in wide area is an important and yet challenging issue of intelligent visual surveillance multi-camera collaboration tracking approach has been becoming attractive. In this work, a flexible and integrated system is constructed for object tracking using multiple cameras either with overlapping fields of views (FOVs), non-overlapping FOVs or mixed configurations for wide areas surveillance. The Kalman filter is applied for object tracking in a single camera and object motion prediction is implemented across blind regions for non-overlapping FOVs. Furthermore, a client and server architecture is constituted using TCP/IP network. The FOV lines are used to guide camera switching. In addition, we integrate various features for object matching. Finally, this system can track objects in a wide area no matter the FOVs are overlapping, non-overlapping or mixed situations.
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Responses of Eukaryotic Cells to Oxidative Stress
Dawes, Ian W. The Korean Society for Applied Biological Chemistr 2000 Journal of Applied Biological Chemistry (J. Appl. Vol.43 No.4
Oxidative stress is implicated in a number of diseases, in ageing of organisms, and in damage to plants that have been exposed to freezing and thawing or water stress. From the perspective of yeast as a model eukaryotic system, this article reviews the systems that are involved in the cellular responses to exposure to reactive oxygen species (ROS) generated during aerobic growth of the organism. The discussion includes the defense systems involved, the ability of cells to adapt to ROS treatment, cell-division cycle delay and the systems regulating gene expression that are activated by oxidative stress.
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