• Smart Structures and Systems
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• 제5권1호
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• pp.23-42
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• 2009

In order to reduce vibration or to control shape of structures made of metal or composites, piezoelectric materials have been extensively used since their discovery in 1880's. A recent trend is also seen to apply piezoelectric materials to flexible structures made of rubber-like materials. In this paper a non-linear finite element model using updated Lagrangian (UL) approach has been developed for static analysis of rubber-elastic material with surface-bonded piezoelectric patches. A compressible stain energy function has been used for modeling the rubber as hyperelastic material. For formulation of the nonlinear finite element model a twenty-node brick element is used. Four degrees of freedom u, v and w and electrical potential ${\varphi}$ per node are considered as the field variables. PVDF (polyvinylidene fluoride) patches are applied as sensors/actuators or sensors and actuators. The present model has been applied to bimorph PVDF cantilever beam to validate the formulation. It is then applied to study the smart rubber components under different boundary and loading conditions. The results predicted by the present formulation are compared with the analytical solutions as well as the available published results. Some results are given as new ones as no published solutions available in the literatures to the best of the authors' knowledge.

• 한국기계가공학회지
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• 제21권5호
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• pp.1-8
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• 2022

Fused deposition modeling (FDM), based on stacking a continuous filament of polymer or composite materials, is well matured and is thus widely used in additive manufacturing technology. To advance FDM-based 3D printing technology, the mechanical properties of additively manufactured composite materials must be improved. In this study, we proposed a novel FDM 3D printing process using metal wire-polymer composites, enabling enhanced mechanical properties. In addition, we developed a new type FDM filament of copper wire wrapped in nylon material for stable 3D printing without thermal damage during the printing process. After FDM printing of the copper wire-nylon composite filament, we conducted a tensile test to investigate the mechanical behavior of the printed composite materials. The experimental results confirmed that the tensile strength of the 3D-printed metal wire-polymer composites was higher than that of the conventional single polymer material. Thus, we expect that the FDM printing process developed in this study may be promising for high-load-bearing applications.

• Elastomers and Composites
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• 제58권4호
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• pp.208-215
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• 2023

In this study, the properties of polyurethane-polydimethylsiloxane (PU-PDMS) hybrid foams containing different types and contents of physical blowing agents (PBAs) were investigated. Two types of blowing agents, namely physical blowing agents and thermally expandable microspheres (TEM), were applied. The apparent density was measured using precisely cut foam samples, and the pore size was measured using image software. In addition, the microstructure of the foam was confirmed via scanning electron microscopy and transmission electron microscopy. The thermal conductivities related to the microstructures of the different foams were compared. When 0.5 phr of the hydrocarbon-based PBA was added, the apparent density and pore size of the foam were minimal; however, the pore size was larger than that of neat foam. In contrast, the addition of 3 phr of TEM effectively reduced both the apparent density and pore size of the PBAs. The increase in resin viscosity owing to TEM could enhance bubble production stability, leading to the formation of more uniform and smaller pores. These results indicate that TEM is a highly efficient PBA that can be employed to decrease the weight and pore size of PU-PDMS hybrid foams.

• 대한공업교육학회지
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• 제39권1호
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• pp.102-127
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• 2014

이 연구의 목적은 교사들의 스마트교육 수업능력 향상을 위하여, 스마트교육 교사연수 프로그램을 개발하는데 있으며, 이를 위하여 분석-설계-개발-실행-평가 의 다섯 단계로 구성된 스마트교육 교사연수 프로그램 개발 절차를 설정하였다. 프로그램의 구체적인 내용구성을 위하여 환경분석, 학습자분석, 과제분석을 실시하였고, 그 결과를 반영하여 스마트교육 이론과 실제, 스마트교육 플랫폼 활용, 스마트 교수 학습 솔루션, 스마트교육 학교교실 운영사례, 스마트교육실습과 스마트 디바이스 중독의 5개 주제와 12개의 학습과제를 설계하였다. 요구분석 및 설계 결과를 바탕으로 스마트교육 교사연수 프로그램의 교재와 수업매체를 개발하였으며, 개발된 프로그램은 교원연수기관으로 지정된 스마트교육 연구센터를 통하여 D시의 초등 및 중등교사 72명에게 적용하여 연수를 실시하였다. 연수결과에서 나타난 참여교사들의 평가와 전문가 협의를 통하여 스마트 교육 교사연수 프로그램을 완성하였다. 또한 프로그램 개발과정을 통해 나타난 스마트교육 교사연수 프로그램의 논의를 바탕으로 향후 스마트교육 교사연수 프로그램 개발을 위한 시사점을 제공하고자 하였다.

• 컴퓨터교육학회논문지
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• 제16권3호
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• pp.31-39
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• 2013

본 연구는 교수자와 학습자들이 소유하고 있는 여러 장치들을 활용한다는 개념을 이용하여 스마트러닝 환경을 지원할 수 있는 학습자 평가시스템을 개발하여 수업에 적용하였다. 또한, 인터페이스, 상호작용, 애플리케이션, 기술지원, 평가 영역을 통해 학습자의 만족도를 분석하였다. 개발된 시스템은 태블릿 PC와 스마트폰용 애플리케이션 프로그램, 프로젝터를 지원하는 전자교탁용 프로그램, 서버 프로그램으로 구성된다. 수업자료 및 학습자에 대한 평가, 피드백 자료는 모두 서버에 저장되며, 학습자는 이를 이용하여 스마트폰, 데스크탑 PC를 통해 학습하거나 수업에 대한 피드백을 실시간 받을 수 있게 하였다. 제안된 시스템을 이용할 경우 학습자의 학업성취도와 학습에 대한 흥미를 높일 수 있음을 보이고 있다.

• Smart Structures and Systems
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• 제16권3호
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• pp.555-577
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• 2015

In the work at hand, the development of a morphing flap, actuated through shape memory alloy load bearing elements, is described. Moving from aerodynamic specifications, prescribing the morphed shape enhancing the aerodynamic efficiency of the flap, a suitable actuation architecture was identified, able to affect the curvature. Each rib of the flap was split into three elastic elements, namely "cells", connected each others in serial way and providing the bending stiffness to the structure. The edges of each cell are linked to SMA elements, whose contraction induces rotation onto the cell itself with an increase of the local curvature of the flap airfoil. The cells are made of two metallic plates crossing each others to form a characteristic "X" configuration; a good flexibility and an acceptable stress concentration level was obtained non connecting the plates onto the crossing zone. After identifying the main design parameters of the structure (i.e. plates relative angle, thickness and depth, SMA length, cross section and connections to the cell) an optimization was performed, with the scope of enhancing the achievable rotation of the cell, its ability in absorbing the external aerodynamic loads and, at the same time, containing the stress level and the weight. The conceptual scheme of the architecture was then reinterpreted in view of a practical realization of the prototype. Implementation issues (SMA - cells connection and cells relative rotation to compensate the impressed inflection assuring the SMA pre-load) were considered. Through a detailed FE model the prototype morphing performance were investigated in presence of the most severe load conditions.

• ETRI Journal
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• 제32권3호
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• pp.414-421
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• 2010

The interconnection mechanisms of a smart anisotropic conductive adhesive (ACA) during processing have been characterized. For an understanding of chemorheological mechanisms between the fluxing polymer and solder powder, a thermal analysis as well as solder wetting and coalescence experiments were conducted. The compatibility between the viscosity of the fluxing polymer and melting temperature of solder was characterized to optimize the processing cycle. A fluxing agent was also used to remove the oxide layer performed on the surface of the solder. Based on these chemorheological phenomena of the fluxing polymer and solder, an optimum polymer system and its processing cycle were designed for high performance and reliability in an electrical interconnection system. In the present research, a bonding mechanism of the smart ACA with a polymer spacer ball to control the gap between both substrates is newly proposed and investigated. The solder powder was used as a conductive material instead of polymer-based spherical conductive particles in a conventional anisotropic conductive film.

• 한국소음진동공학회논문집
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• 제19권2호
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• pp.138-145
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• 2009

Structural vibration and noise are hot issues in underwater vehicles such as submarines for their survivability. Therefore, active vibration and noise control of submarine, which can be modeled as hull structure, have been conducted by the use of piezoelectric materials. Traditional piezoelectric materials are too brittle and not suitable to curved geometry such as hull structures. Therefore, advanced anisotropic piezocomposite actuator named as Macro-Fiber Composite(MFC), which can provide great flexibility, large induced strain and directional actuating force is adopted for this research. In this study, dynamic model of the smart hull structure is established and active vibration control performance of the smart hull structure is evaluated using optimally placed MFC. Actuating performance of MFC is evaluated by finite element analysis and dynamic modeling of the smart hull structure is derived by finite element method considering underwater condition. In order to suppress the vibration of hull structure, Linear Quadratic Gaussian(LQG) algorithm is adopted. After then active vibration control performance of the proposed smart hull structure is evaluated with computer simulation and experimental investigation in underwater. Structural vibration of the hull structure is decreased effectively by applying proper control voltages to the MFC actuators.

• 패션비즈니스
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• 제22권6호
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• pp.94-104
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• 2018

The objective of this study was to develop a wearable systems that protect users, based on sensors that are easy to use, from accidents caused by harmful gases in the operator's poor working environment or the risk of ultraviolet rays during outdoor activities. By developing smart wappen with Light Emitting Diode (LED) light alarm function including UV sensor and gas sensor and central processing unit, systems that are applied to daily wear and work clothes to explore the possibility of user-centered, harmful environment monitoring products in real time were proposed. Each sensor was applied to sportswear and work clothes and the wappen system consisted of lightweight and thin form as a whole. Wappen to cover the device had one sheet cover on the front and another cover from the inside to form a sandwich like formation. Wappen was made in the same form as regular clothes that doesn't damage the exterior then a removable wappen system was developed using Velcro and snap methods to enable the separation of device or the exchange of batteries. De-adhesion method can occur in two ways, from the outside and from the inside, so the design is selected depending on the application. This study shows the significance of the development of sensor-based smart clothing, in that it presented a universal model for users.

• Steel and Composite Structures
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• 제50권6호
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• pp.609-625
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• 2024

This paper presents an in-depth analysis of the nonlinear vibration of microbeams, with a particular emphasis on their application in sports monitoring systems. The research utilizes classical beam theory, modified couple stress theory, and von-Kármán nonlinear parameters to explore the behavior of microbeams. These microbeams are characterized by a non-uniform geometry, with materials that continuously change along the beam radius and a thickness that varies along the beam length. The main contribution lies in its exploration of the stability of smart sensors in sports structures, particularly those with non-uniform geometries. The research findings indicate that these non-uniform microbeams, when used in smart systems made of functionally graded temperature-dependent materials, can operate effectively in thermal environments. The smart system developed in this study demonstrates significant potential for use in sports applications, particularly in monitoring and gathering information. The insights gained from this research contribute to the understanding of the performance and optimization of microbeams in sports applications, particularly in the context of non-uniform geometries. This research, therefore, provides a foundation for the development of advanced, reliable, and efficient monitoring systems in sports applications.