• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.165-165
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• 2014

In this study, we demonstrated that the soft lithographic patterning processing of chemical vapor deposition (CVD) graphene and rGO sheets as large scale, low cost, high quality and simplicity for future industrial applications. Recently, a previous study has reported that single layer graphene grown via CVD was patterned and transferred to a target surface by controlling the surface energy of the polydimethylsiloxane (PDMS) stamp [1]. Using this approach, the surface of a relief-patterned elastomeric stamp was functionalized with hydrophilic dimethylsulfoxide (DMSO) molecules to enhance the surface energy of the stamp and to remove the graphene-based layer from the initial substrate and transfer it to a target surface [2]. Further, we developed a soft lithographic patterning process via surface energy modification for advanced graphene-based flexible devices such as transistors or simple and efficient chemical sensor consisting of reduced graphene oxide (rGO) and a metallic nanoparticle composite. A flexible graphene-based device on a biocompatible silk fibroin substrate, which is attachable to an arbitrary target surface, was also successfully fabricated.

• 한국구조물진단유지관리공학회 논문집
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• 제17권1호
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• pp.37-45
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• 2013

본 연구에서는 다양한 RC 슬래브의 접촉 발파 실험을 수행하여 내폭 성능을 평가하였다. RC 슬래브의 내폭 성능 향상을 위해 섬유 보강과 외부 CFRP 시트 보강을 도입하였다. 폭발하중 실험은 $2,000{\times}1,000{\times}100mm$ RC 슬래브를 제작하였고, 일반 콘크리트와 강섬유 보강 콘크리트, 하이브리드 PVA 섬유 보강 시멘트 복합체, 초고성능 콘크리트를 적용하였다. 접촉 발파로 생긴 RC 슬래브의 손상 정도를 크레틀, 스폴과 브리치의 직경과 깊이로 평가하였다. 실험 결과를 LS-DYNA 유한요소해석 프로그램과 Morishita 등의 예측식으로 검증하고 비교분석하였다. 분석 결과, LS-DYNA 프로그램을 이용하여 크레틀, 스폴, 브리치의 직경 및 깊이에 대한 개략적인 예측이 가능하며, 폭발하중 하에서 손상부의 거시적 거동을 모사함으로써 부재의 파괴 이력을 나타낼 수 있었다. 국부 손상에 대한 세가지 예측식이 소개되어 있으나 경험식으로써의 한계가 존재하며, 이에 대한 추가 연구가 필요하다고 판단된다.

• 공업화학
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• 제7권3호
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• pp.424-432
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• 1996

열가소성 고분자 복합재료 개발을 위하여 매트릭스수지로는 폴리프로필렌(PPF) 섬유를 사용하고 유기계 강화섬유로 비닐론(VF), 아라미드(KF) 및 나일론(PAF) 섬유 등을 사용하여 복합매트를 얻은다음 압축 성형하여 고분자 복합재료를 제조하였다. 제조한 고분자 복합재료의 충격 특성 및 형태학적 특성 등을 측정하였다. 아이조드충격강도는 VF/PP가 크며, 고속충격특성은 KF/PP계가 약간 크게 나타났다. Ductility Index(Dl)는 VF/PP>KF/PP>PAF/PP 순으로 나타났으며 VF/PP의 최대 DI값은 섬유중량분율이 20%일 때 2.43이었다. 유기섬유 충전률은 20~30%가 최적값이었으며 SEM 관찰로 섬유분산상태 및 배향성은 양호함을 확인하였다. 결론적으로 VF/PP 복합재료가 KF/PP 및 PAF/PP 복합재료에 비해 계면접착력이 가장 우수하였다.

• 한국전기전자재료학회논문지
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• 제28권12호
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• pp.792-796
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• 2015

With high integration of electronic components, power inductors are also miniaturized. Recently, thick film processes for small size power inductors were developed and commercialized. However, the thick film process to prepare soft magnetic green sheets was not reported enough. In this study, we used Fe-Si magnetic and CIP (carbonyl iron powders) as starting materials to lead to a bimodal particle size distribution in the sheet. We proposed a newly developed 'Modified slurry preparation process' to get well dispersed condition even at high solid contents. Using the new process, it was possible to prepare a well dispersed slurry over 70 vol% of solid. BYK-103 was better than BYK-111 as dispersant in this slurry and the optimum amount was 0.6 wt%. The optimized slurry was formed into a sheet by tape casting process and then the sheet was laminated. We conformed that small size powder, large size powder, and epoxy resin were well dispersed in the green sheet.

• 자원리싸이클링
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• 제17권3호
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• pp.10-20
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• 2008

농업용 폐비닐의 재활용에 대한 무기충진재의 거동을 연구하기 위하여 한국환경자원공사 시화 및 정읍공장에서 세척된 PE fluff들을 각각 사용하였다. 먼저 PE 플러프에 무기충진재인 탄산칼슘과 칼펫을 배합비율별로 혼합하여 용융 압출을 통한 시험용 펠렛들을 제조한 후 프레스 몰딩을 거쳐 시료별로 시험용 시트들을 제작하였다. 이들 무기충진 복합재의 기계적 특성인 인장, 굴곡, Izod 충격시험을 실시하였고, 열적 특성인 열변형온도, vicat 연화온도, 용융흐름지수(MFI)를 시험 및 분석을 하였다. 또한 플라스틱 내부에서 무기충진재의 분산성 및 wetting정도를 확인하기 위하여 SEM을 통해 모폴로지를 조사하였다. 이들 결과로부터 물리적인 측면과 경제적인 관점에서 재생 PE와 무기충진재의 최적 배합비들을 얻었다.

• Steel and Composite Structures
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• 제33권5호
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• pp.717-727
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• 2019

This paper is motivated by the lack of studies in the technical literature concerning to vibration analysis of a single-layered graphene sheet (SLGS) with corner cutout based on the nonlocal elasticity model framework of classical Kirchhoff thin plate. An isogeometric analysis (IGA) based upon non-uniform rational B-spline (NURBS) is employed for approximation of the L-shape SLGS deflection field. Trimming technique is employed to create the cutout in geometry of L-shape plate. The L-shape plate is assumed to be Free (F) in the straight edges of cutout while any arbitrary boundary conditions are applied to the other four straight edges including Simply supported (S), Clamped (C) and Free (F). The Numerical studies are carried out to express the influences of the nonlocal parameter, cutout dimensions, boundary conditions and mode numbers on the variations of the natural frequencies of SLGS. It is precisely shown that these parameters have considerable effects on the free vibration behavior of the system. In addition, numerical results are validated and compared with those achieved using other analysis, where an excellent agreement is found. The effectiveness and the accuracy of the present IGA approach have been demonstrated and it is shown that the IGA is efficient, robust and accurate in terms of nanoplate problems. This study serves as a benchmark for assessing the validity of numerical methods used to analyze the single-layered graphene sheet with corner cutout.

• Computers and Concrete
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• 제23권1호
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• pp.61-68
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• 2019

This paper presents a computational rational model to predict the ultimate and optimized load capacity of reinforced concrete (RC) beams strengthened by a combination of longitudinal and transverse fiber reinforced polymer (FRP) composite plates/sheets (flexure and shear strengthening system). Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. A high performance concrete, known as polymer concrete, made up of natural aggregates and an orthophthalic polyester binder, reinforced with non-metallic bars (glass reinforced polymer) has been studied. The material is described at micro and macro level, presenting the key physical and mechanical properties using different experimental techniques. Furthermore, a full description of non-metallic bars is presented to evaluate its structural expectancies, embedded in the polymer concrete matrix. In this paper, the mechanism of mechanical interaction of smooth and lugged FRP rods with concrete is presented. A general modeling and application of various elements are demonstrated. The contact parameters are defined and the procedures of calculation and evaluation of contact parameters are introduced. The method of calibration of the calculated parameters is presented. Finally, the numerical results are obtained for different bond parameters which show a good agreement with experimental results reported in literature.

• Journal of the Korean Wood Science and Technology
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• 제50권2호
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• pp.134-147
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• 2022

The objective of this study is to determine the effect of fiber direction arrangement and layer composition of hybrid bamboo laminate boards on the physical and mechanical properties. The raw material used was tali bamboo (Gigantochloa apus (J.A. & J.H. Schultes) Kurs) rope in the form of flat sheets (zephyr) and falcata veneer (Paraserianthes falcataria (L) Nielsen). Zephyr bamboo was arranged in three layers using water-based isocyanate polymer (WBPI) with a glue spread rate of 300 g/m². There were variations in the substitution of the core layer with falcata veneers (hybrid) as much as two layers and using a glue spread rate of 170 g/m². The laminated bamboo board was cold-pressed at a pressure of 22.2 kgf/cm² for 1 h, and the physical and mechanical properties were evaluated. The results showed that the arrangement of the fiber direction significantly affected the dimensional stability, modulus of rupture, modulus of elasticity, shear strength, and screw withdrawal strength. However, the composition of the layers had no significant effect on the physical and mechanical properties. The bonding quality of bamboo laminate boards with WBPI was considered to be quite good, as shown by the absence of delamination in all test samples. The bamboo hybrid laminate board can be an alternative based on the physical and mechanical properties that can meet laminated board standards.

• Steel and Composite Structures
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• 제46권1호
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• pp.1-13
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• 2023

Elastic bending of imperfect functionally graded sandwich plates (FGSPs) laying on the Winkler-Pasternak foundation and subjected to sinusoidal loads is analyzed. The analyses have been established using the quasi-3D sinusoidal shear deformation model. In this theory, the number of unknowns is condensed to only five unknowns using integral-undefined terms without requiring any correction shear factor. Moreover, the current constituent material properties of the middle layer is considered homogeneous and isotropic. But those of the top and bottom face sheets of the graded porous sandwich plate (FGSP) are supposed to vary regularly and continuously in the direction of thickness according to the trigonometric volume fraction's model. The corresponding equilibrium equations of FGSPs with simply supported edges are derived via the static version of the Hamilton's principle. The differential equations of the system are resolved via Navier's method for various schemes of FGSPs. The current study examine the impact of the material index, porosity, side-to-thickness ratio, aspect ratio, and the Winkler-Pasternak foundation on the displacements, axial and shear stresses of the sandwich structure.

• Steel and Composite Structures
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• 제51권1호
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• pp.73-91
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• 2024

This paper has focused on presenting vibration analysis of trapezoidal sandwich plates with a damaged core and FG wavy CNT-reinforced face sheets. A damage model is introduced to provide an analytical description of an irreversible rheological process that causes the decay of the mechanical properties, in terms of engineering constants. An isotropic damage is considered for the core of the sandwich structure. The classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The First-order shear deformation theory of plate is utilized to establish governing partial differential equations and boundary conditions for the trapezoidal plate. The governing equations together with related boundary conditions are discretized using a mapping-generalized differential quadrature (GDQ) method in spatial domain. Then natural frequencies of the trapezoidal sandwich plates are obtained using GDQ method. Validity of the current study is evaluated by comparing its numerical results with those available in the literature. After demonstrating the convergence and accuracy of the method, different parametric studies for laminated trapezoidal structure including carbon nanotubes waviness (0≤w≤1), CNT aspect ratio (0≤AR≤4000), face sheet to core thickness ratio (0.1 ≤ ${\frac{h_f}{h_c}}$ ≤ 0.5), trapezoidal side angles (30° ≤ α, β ≤ 90°) and damaged parameter (0 ≤ D < 1) are carried out. It is explicated that the damaged core and weight fraction, carbon nanotubes (CNTs) waviness and CNT aspect ratio can significantly affect the vibrational behavior of the sandwich structure. Results show that by increasing the values of waviness index (w), normalized natural frequency of the structure decreases, and the straight CNT (w=0) gives the highest frequency. For an overall comprehension on vibration of laminated trapezoidal plates, some selected vibration mode shapes were graphically represented in this study.