• Journal of the Korean Society for Precision Engineering
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• v.33 no.10
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• pp.875-880
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• 2016

In this study, we proposed an effective and simple way to directly generate wrinkle patterns on a curved surface. A curved surface was prepared using a 3D printer and an UV (Ultraviolet)-lighting system was utilized to weakly polymerize the UV-curable thin resin layer coated on the surface, resulting in a gradient of material properties in the layer thickness. Subsequently, a thermal curing process was conducted to generate microscale wrinkles by compressive forces that were generated during complete curing. Wrinkle shapes from 5, 15, 25 sec of UV-light exposure were compared. With increasing UV-exposure, the line-width of wrinkles became thicker due to much higher strength of skin zone. The results indicated that the proposed fabrication process could be utilized for surface modification in diverse research fields.

• Journal of Astronomy and Space Sciences
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• v.31 no.2
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• pp.131-140
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• 2014

Lava caves could be useful as outposts for the human exploration of the Moon. Lava caves or lava tubes are formed when the external surface of the lava flows cools more quickly to make a hardened crust over subsurface lava flows. The lava flow eventually ceases and drains out of the tube, leaving an empty space. The frail part of the ceiling of lava tube could collapse to expose the entrance to the lava tubes which is called a pit crater. Several pit craters with the diameter of around 100 meters have been found by analyzing the data of SELENE and LRO lunar missions. It is hard to use these pit craters for outposts since these are too large in scale. In this study, small scale pit craters which are fit for outposts have been investigated using the NAC image data of LROC. Several topographic patterns which are believed to be lunar caves have been found and the similar pit craters of the Earth were compared and analyzed to identify caves. For this analysis, the image data of satellites and aerial photographs are collected and classified to construct a database. Several pit craters analogous to lunar pit craters were derived and a morphological pit crater model was generated using the 3D printer based on this database.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.24-27
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• 2001

Nowadays, increasing demand of the customized products has led to an increased usage of rapid prototyping in the product development. However, the acquisition price of a rapid prototyping equipment is still too high that not every body can afford to buy one. To offer a wide access to the users who need physical prototypes, a connection of the rapid prototyping equipment to the Internet is a viable step. It would allow a large group of customers all over the world to use the manufacturing capability of a service provider offering this kind of manufacturing service. To realize how such an e-manufacturing concept can look like, a LOM-type 3D printer developed at KIST has been used as test site and connected to the Internet. A possible user can log on to the server of the equipment and view his STL file and start the building operation from a remote place. To see whether the operation runs properly, a CCD camera is used to transmit the actual state of operation online. The result so far proves the feasibility of rapid prototyping on the Internet as well as an order-adaptive manufacturing system via web.

• Journal of Korean society of Dental Hygiene
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• v.18 no.5
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• pp.729-740
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• 2018

Objectives: The purpose of this study was to investigate the factors affecting robot utilization in the education of pre-dental hygienists. Methods: A self-reported questionnaire was completed by 238 dental hygiene students studying in the Daejeon, Chungcheong, and Jeolla provinces during the period March 1-31, 2017. Results: Future oral health education media had high selection of 'movies,' 'video,' '3D printer,' 'robot,' and 'drone' In general education and oral health education, robots were appropriate as educators, assistant teachers, and media. This group had high levels of interest, experience, attitude, and learning scope of robots. Robot utilization education showed a significant positive correlation with the 'interest,' 'experience,' 'attitude,' and 'learning' subfactors (p<0.01). Factors influencing robot utilization education were the relationships among actual experience of robot, learning of robot production, social influence of robot, emotional exchange with robot, and the predictive power was 25.5% (p<0.05). Conclusions: Oral health education curricula using robots should be developed considering the emotional exchange and social influence between educator and learner.

• Journal of the Korean Society of Visualization
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• v.16 no.2
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• pp.45-52
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• 2018

The tangential and axial cyclones were fabricated using a 3D printer and the total collecting efficiency, cut-diameter, and pressure drop characteristics of the two types of cyclones with the same inlet area were investigated experimentally. The results show that the total collecting efficiency tends to increase as the inlet velocity increases. However, at a 20m/s condition of the tangential cyclone, the collected particles were re-entrained to the ascending vortex flow, resulting in a decrease of the total collecting efficiency. In the axial cyclone, the cross-sectional area is designed to increase at the inlet and the velocity is reduced, so that the re-entrainment effect does not appear in this study. The pressure loss of the tangential cyclone was larger than that of the axial cyclone. The cut-diameter tends to decrease with increasing the inlet velocity in two types of cyclones, except for the 20m/s condition of the tangential cyclone.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.5
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• pp.103-111
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• 2008

This study proposes a technique to estimate the material property of a paper by using an experimental methods and commercial CAE software. Under gravitation, if one side of the paper is attached to the ground, the opposite side of paper is largely deformed, and vibrates freely. Since the paper has an orthotropic characteristic due to its treatment, the deformations in two orthogonal directions of the dry paper are different. An experimental method to measure the static deformation of the paper introduces this phenomenon. And dynamic behavior, frequency of free vibration is measured. And then. virtual prototypes that can represent the static and dynamic behavior are modeled by using the commercial CAE software $RecurDyn^{MT}$/MTT3D, which has been widely used by the printer makers. While comparing the deformation and frequency from the experiment and simulation, a design optimization technique in the commercial CAE software of R-INOPL, $RecurDyn^{TM}$/AutoDesign is used to estimate the material property such as Young's modulus, shear modulus and density of the paper.

• International Journal of Aerospace System Engineering
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• v.5 no.2
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• pp.1-7
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• 2018

This study examines the history of Korean aviation industry and presents the investment strategy based on the evidence and the 4th industrial revolution. Looking at the evolution of the Korean aviation industry and its technological development will be a great help to support industrial and technological innovation in the future. The modern aviation industry is divided into stages of development, focusing on maintenance of equipment introduced in advanced countries, localization through license assembly, production of products based on technology, and international joint development. The development of aeronautics technology has been progressing towards a general improvement of economic efficiency, aircraft safety efficiency through environmental-friendliness, unmanned operation, and downsizing. The Korea Aerospace Research Institute has secured key technologies through development of several aircrafts such as Experimental Aircraft Kachi, EXPO Unmanned Airship, Twin-engine Composite Aircraft, Canard Aircraft, Multi-Purpose Stratosphere unmanned-airship, Medium Aerostats, Smart UAV, Surion, EAV-2H, KC-100, and OPV. The development strategy is discussed at the level of the evidence-based investment strategy that is currently being discussed, and so the investment priorities in aircraft is high. Current drone usage and development direction are not only producing parts using 3D printer, but also autonomous flight, communication (IoT, 5G), information processing (big data, machine learning). Therefore, the aviation industry is expected to lead the fourth industrial revolution.

• Smart Structures and Systems
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• v.30 no.1
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• pp.35-47
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• 2022

Data-driven engineering is crucial for information delivery between design, fabrication, assembly, and maintenance of prefabricated structures. Design for manufacturing and assembly (DfMA) is a critical methodology for prefabricated bridge structures. In this study, a novel concept of digital engineering model that combined existing knowledge of DfMA with object-oriented parametric modeling technologies was developed. Three-dimensional (3D) geometry models and their data models for each phase of a construction project were defined for information delivery. Digital design models were used for conceptual design, including aesthetic consideration and possible variation during fabrication and assembly. The seismic performance of a bridge pier was evaluated by linking the design parameters to the calculated moment-curvature curves. Control parameters were selected to consider the tolerance control and revision of the digital models. Digitalized fabrication of the prefabricated members was realized using the digital fabrication model with G-code for a concrete printer or a robot. The fabrication error was evaluated and the design digital models were updated. The revised fabrication models were used in the preassembly simulation to guarantee constructability. For the maintenance of the bridge, the as-built information was defined for the prefabricated bridge piers. The results of this process revealed that data-driven information delivery is crucial for lifecycle management of prefabricated bridge piers.

• Journal of the Korean Society of Visualization
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• v.21 no.1
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• pp.110-118
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• 2023

Characterizing the extensional rheological properties of non-Newtonian fluids is crucial in many industrial processes, such as inkjet printing, injection molding, and fiber engineering. However, educational institutions and research laboratories with budget constraints have limited access to an expensive commercial extensional rheometer. In this study, we developed a custom-made extensional rheometer using a CO₂ laser cutting machine and 3D printer. Furthermore, we utilized a smartphone with a low-cost microscopic lens for achieving a high spatial resolution of images. The aqueous polyethylene-oxide (PEO) solutions and a Boger fluid were prepared to characterize their extensional properties. A transition from a visco-capillary to an elasto-capillary regime was observed clearly through the developed rheometer. The extensional relaxation time and viscosity of the aqueous PEO solutions with a zero-shear viscosity of over 300 mPa·s could be quantified in the elasto-capillary regime. The extensional properties of the solutions with relatively small zero shear viscosity could be calculated using a smartphone's slow-motion feature with increasing temporal resolution of the images.

• Transactions of Materials Processing
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• v.32 no.1
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• pp.28-34
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• 2023

In this research, a representative volume element (RVE)-based FE Model is presented to estimate the mechanical properties of additively manufactured continuous fiber-reinforced composites with different fiber orientations. To construct the model, an ABAQUS Python script has been implemented to produce matrix and fiber in the desired orientations at the RVE. A script has also been developed to apply the periodic boundary conditions to the RVE. Experimental tests were conducted to validate the numerical models. Tensile specimens with the fiber directions aligned in the 0, 45, and 90 degrees to the loading direction were manufactured using a continuous fiber 3D printer and tensile tests were performed in the three directions. Tensile tests were also simulated using the RVE models. The predicted Young's moduli compared well with the measurements: the Young's modulus prediction accuracy values were 83.73, 97.70, and 92.92 percent for the specimens in the 0, 45, and 90 degrees, respectively. The proposed method with periodic boundary conditions precisely evaluated the elastic properties of additively manufactured continuous fiber-reinforced composites with complex microstructures.