• 대한치과보철학회지
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• 제55권3호
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• pp.305-310
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• 2017

최근, CAD/CAM 기술이 발전하면서 하이브리드 보철물의 제작에 이용되고 있다. Double scanning technique은 시적용 납의치와 주모형을 스캔 후 중첩하여, 가상 디자인의 현실화와 보철 기공 과정의 간소화를 이루었다. 본 증례에서는 금속 혹은 지르코니아 대신 고성능 중합체인 Polyetherketoneketone (Pekkton, Cendres+$M{\acute{e}}taux$, Biel, Switzerland)를 framework의 재료로 사용했으며, 콤포짓이나 세라믹 혹은 의치용 치아 대신 Polymethyl methacrylate (PMMA) 비니어링 치아(Visio-lign, Bredent, Senden, Germany)를 최종 보철물로 사용하였다. Pekkton과 Visio-lign을 사용한 본 증례에서 만족할만한 치료 결과와 환자의 만족을 얻었으며, 추후 주기적인 유지관리 및 평가가 필요할 것으로 사료된다.

• 한국정밀공학회지
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• 제26권7호
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• pp.44-50
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• 2009

High-pressured jetting is now widely used in the advanced cutting processes of polymers, metals, glass, ceramics and composite materials because of some advantages such as heatless and non-contacting cutting. Similarly to the focused laser beam machining, it is well known as a type of high-density energy processes. High-pressured jetting is going to be developed not only to minimize the cutting line width but also to achieve the short cutting time as soon as possible. However, the interaction behavior between a work piece and high-velocity abrasive particles during the high-pressured jet cutting makes the impact mechanism even more complicated. Conventional high-pressured jetting is still difficult to apply to precision cutting of micro-scaled thin work piece such as thin metal sheets, thin ceramic substrates, thin glass plates and TMM (Thin multi-layered materials). In this paper, we proposed the advanced high-pressured jetting technology by introducing a new abrasives supplying method and investigated the optimal process conditions of the cutting pressure, the cutting velocity and SOD (Standoff distance).

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.58.1-58.1
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• 2011

WC-Co and other similar cemented carbides have been widely used as hard materials in industrial cutting tools and as mould metals; and a number of techniques have been applied to improve its microstructural characteristics, hardness and ear resistance. Cobalt is used primarily to facilitate liquid phase sintering and acts as a matrix, i.e. a cementing phase between WC grains. A uniform distribution of metal phase in a ceramic is beneficial for improved mechanical properties of the composite. WC-Co, starting from initial powders, is vastly used for a variety of machining, cutting, drilling, and other applications because of its unique combination of high strength, high hardness, high toughness, and moderate modulus of elasticity, especially with fine grained WC and finely distributed cobalt. In this study, that started with two different compositions of initial powders, WC-7.5wt%Co and WC-12wt%Co with initial powder size being 1~3 ${\mu}m$, magnetic pulsed compaction followed by subsequent vacuum sintering were carried out to produce consolidated preforms. Magnetic Pulsed Compaction (MPC), a very short duration (~600 ${\mu}s$), high pressure (~4 Gpa), high-density preform molding method was used with varied pressure between 0.5 and 3.0 Gpa, in order to reach an initial high density that would help improve the sintering behavior. For both compositions and varied MPC pressure, before and after sintering, changes in microstructural behavior and mechanical properties were analyzed. With proper combination of MPC pressure and sintering, samples were obtained with better mechanical properties, densification and microstructural behavior, and considerably improved than other conventional processes.

• 한국결정성장학회지
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• 제22권6호
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• pp.279-285
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• 2012

BCP, Mg-BCP, Si-BCP 분말을 공침법(co-precipitation process)을 이용하여 합성하였다. 제조된 분말을 X-선 회절 분석(XRD), 적외선분광분석(FTIR)을 이용하여 특성을 분석하였다. Ca/P 몰 비율이 1.602인 칼슘 결손 아파타이트 공침물을 제조하여 $1000^{\circ}C$ 열처리 과정을 통하여 HAp와 ${\beta}$-TCP 상이 혼재된 BCP, Mg-BCP, Si-BCP을 합성할 수 있었다. 제조된 분말의 생체활성 거동을 평가하기 위하여 Hanks' Balanced Salt Solution(HBSS)에 침적시켜 시간에 따라 형상의 변화 및 결정상을 분석한 결과, BCP 분말에 비하여 금속 이온이 치환된 BCP 분말에서 빠른 생체활성을 관찰할 수 있었다. MTT assay를 통한 세포 성장률 평가에서모든 분말에서 시간 경과에 따라 독성을 나타내지 않았으며, 세포의 활성이 증가하였다.

• Steel and Composite Structures
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• 제19권2호
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• pp.369-384
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• 2015

This work presents a free vibration analysis of functionally graded metal-ceramic (FG) beams with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. For this purpose, a simple displacement field based on higher order shear deformation theory is implemented. The proposed theory is based on the assumption that the transverse displacements consist of bending and shear components in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments. The most interesting feature of this theory is that it accounts for a quadratic variation of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the beam without using shear correction factors. In addition, it has strong similarities with Euler-Bernoulli beam theory in some aspects such as equations of motion, boundary conditions, and stress resultant expressions. The rule of mixture is modified to describe and approximate material properties of the FG beams with porosity phases. By employing the Hamilton's principle, governing equations of motion for coupled axial-shear-flexural response are determined. The validity of the present theory is investigated by comparing some of the present results with those of the first-order and the other higher-order theories reported in the literature. Illustrative examples are given also to show the effects of varying gradients, porosity volume fraction, aspect ratios, and thickness to length ratios on the free vibration of the FG beams.

• Steel and Composite Structures
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• 제41권6호
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• pp.899-910
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• 2021

A 4-unknown shear deformation theory is applied to investigate the vibration of functionally graded plates under thermal environment. The plate is fabricated from a functionally graded material mixed of ceramic and metal with continuously varying material properties through the plate thickness. Three types of thermal loadings, uniform, linear and nonlinear temperature rises along the plate thickness are taken into account. The present theory contains four unknown functions as against five or more in other higher order shear deformation theories. The through-the-thickness distributions of transverse shear stresses of the plate are considered to vary parabolically and vanish at upper and lower surfaces. The present model does not require any problem dependent shear correction factor. Analytical solutions for the free vibration analysis are derived based on Fourier series that satisfy the boundary conditions (Navier's method). Benchmark solutions are firstly considered to evaluate the accuracy of the proposed model. Comparisons with the solutions available in literature revealed the good capabilities of the present model for the simulations of vibration responses of FG plates. Some parametric studies are carried out for the frequency analysis by varying the volume fraction profile and the temperature distribution across the plate thickness.

• Steel and Composite Structures
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• 제43권6호
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• pp.821-837
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• 2022

This research is devoted to study the effects of humidity and temperature on the bending behavior of functionally graded (FG) ceramic-metal porous plates resting on Pasternak elastic foundation using a quasi-3D hyperbolic shear deformation theory developed recently. The present plate theory with only four unknowns, takes into account both transverse shear and normal deformations and satisfies the zero traction boundary conditions on the surfaces of the functionally graded plate without using shear correction factors. Material properties of porous FG plate are defined by rule of the mixture with an additional term of porosity in the through-thickness direction. The governing differential equations are obtained using the "principle of virtual work". Analytically, the Navier method is used to solve the equations that govern a simply supported FG porous plate. The obtained results are checked by comparing the results determined for the perfect and imperfect FG plates with those available in the scientific literature. Effects due to material index, porosity factors, moisture and thermal loads, foundation rigidities, geometric ratios on the FG porous plate are all examined. Finally, this research will help us to design advanced functionally graded materials to ensure better durability and efficiency for hygro-thermal environments.

• Steel and Composite Structures
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• 제45권5호
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• pp.729-747
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• 2022

The critical buckling loads and buckling modes of bi-directional functionally graded porous unified higher order shear plate with elastic foundation are investigated. A mathematical model based on neutral axis rather than midplane is developed in comprehensive way for the first time in this article. The material constituents form ceramic and metal are graded through thickness and axial direction by the power function distribution. The voids and cavities inside the material are proposed by three different porosity models through the thickness of plate. The constitutive parameters and force resultants are evaluated relative to the neutral axis. Unified higher order shear plate theories are used to satisfy the zero-shear strain/stress at the top and bottom surfaces. The governing equilibrium equations of bi-directional functionally graded porous unified plate (BDFGPUP) are derived by Hamilton's principle. The equilibrium equations in the form of coupled variable coefficients partial differential equations is solved by using numerical differential integral quadrature method (DIQM). The validation of the present model is presented and compared with previous works for bucking. Deviation in buckling loads for both mid-plane and neutral plane are developed and discussed. The numerical results prove that the shear functions, distribution indices, boundary conditions, elastic foundation and porosity type have significant influence on buckling stability of BDFGPUP. The current mathematical model may be used in design and analysis of BDFGPU used in nuclear, mechanical, aerospace, and naval application.

• 공업화학
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• 제34권3호
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• pp.221-225
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• 2023

셀룰로오스는 자연의 다양한 공급원에서 쉽게 얻을 수 있는 가장 일반적인 천연 고분자이다. 셀룰로오스의 한 형태인 나노셀룰로오스는 셀룰로오스를 처리해 쉽게 얻을 수 있으며, 그 고유 물성이 상당히 우수하여 광범위한 산업 응용 분야에 사용이 가능하다. 이러한 나노 셀룰로오스는 금속 및 세라믹 필러를 포함하는 고분자 복합재료를 능가하는 뛰어난 기계적 물성 및 열적 안정성을 제공하며, 지속가능한 환경 친화적인 복합소재이다. 이러한 특성을 기반으로 필러, 포장지, 에너지, 의료, 코팅산업 등 다양한 분야에서 광범위하게 연구되고 있다. 본 리뷰에서는 나노셀룰로오스 및 나노복합소재 개발 그리고 응용분야에 대한 연구동향에 대해 고찰해보았다.

• Steel and Composite Structures
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• 제50권3호
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• pp.299-318
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• 2024

The main objective of this paper is to compute the far-field acoustic radiation (sound radiation) of functionally graded plates (FGM) loaded by sinusoidally varying point load subjected to the arbitrary boundary condition is carried out. The governing differential equations for thin functionally graded plates (FGM) are derived using classical plate theory (CPT) and Rayleigh integral using the elemental radiator approach. Four cases, segregated on power-law index k=0,1,5,10, are studied. A novel approach is illustrated to compute sound fields of vibrating FGM plates using the physical neutral surface with an elemental radiator approach. The material properties of the FGM plate for all cases are calculated considering the power law indexes. An in-house MATLAB code is written to compute the natural frequencies, normal surface velocities, and sound radiation fields are analytically calculated using semi-analytical formulation. Ansys is used to validate the computed sound power level. The parametric effects of the power law index, modulus ratios, different constituent of FGM plates, boundary conditions, damping loss factor on the sound power level, and radiation efficiency is illustrated. This work is the benchmark approach that clearly explains how to calculate acoustic fields using a solid layered FGM model in ANSYS ACT. It shows that it is possible to asymptotically stabilize the structure by controlling the intermittent layers' stiffness. It is found that sound fields radiated by the elemental radiators approach in MATLAB, ANSYS and literatures are in good agreement. The main novelty of this research is that the FGM plate is analyzed in the low-frequency range, where the stiffness-controlled region governs the whole analysis. It is concluded that a clamped mono-ceramic FGM plate radiates a lesser sound power level and higher radiation efficiency than a mono-metallic or metal-rich FGM plate due to higher stiffness. It is found that change in damping loss factor does not affect the same constituents of FGM plates but has significant effects on the different constituents of FGM plates.