• 한국분말재료학회지
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• 제26권1호
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• pp.1-5
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• 2019

In this study, porous Mo-5 wt% Cu with unidirectionally aligned pores is prepared by freeze drying of camphene slurry with $MoO_3-CuO$ powders. Unidirectional freezing of camphene slurry with dispersion stability is conducted at $-25^{\circ}C$, and pores in the frozen specimens are generated by sublimation of the camphene crystals. The green bodies are hydrogen-reduced at $750^{\circ}C$ and sintered at $1000^{\circ}C$ for 1 h. X-ray diffraction analysis reveals that $MoO_3-CuO$ composite powders are completely converted to a Mo-and-Cu phase without any reaction phases by hydrogen reduction. The sintered bodies with the Mo-Cu phase show large and aligned parallel pores to the camphene growth direction as well as small pores in the internal walls of large pores. The pore size and porosity decrease with increasing composite powder content from 5 to 10 vol%. The change of pore characteristics is explained by the degree of powder rearrangement in slurry and the accumulation behavior of powders in the interdendritic spaces of solidified camphene.

• Composites Research
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• 제22권3호
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• pp.60-65
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• 2009

본 인구에서는 탄소섬유강화 복합재 구조물의 실제 사용조건인 환경에 따른 기계적 특성 연구를 수행하기 위하여, $[0_6]_T$, $[90_{12}]_T$, $[0_{16}]_T$, $[{\pm}45]_{5S}$, $[0/9012/0]_T$, $[0/45/-45/45/-45/0]_{3S}$의 실험을 통해, 복합재의 강도와 강성을 측정 하였다. 실험 결과, 환경조건에서 복합재의 파손 거동을 파악하고 설계관련 데이터베이스를 확보하였다. 저은 건조 조건에서 강도의 증가는 저온($-55^{\circ}C$)에서 섬유 촉은 모재의 취성 증가의 요인으로 분석된다. 고온다습 조건의 진단강도와 전단탄성계수 감소는 침투한 수분에 의해 섬유와 모재의 결합부의 물성이 저하한 것으로 분석된다.

• 대한치과보철학회지
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• 제40권5호
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• pp.429-440
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• 2002

Current dental restorations present a relatively weak resistance to fracture. Owing to their unique mechanical properties, fibre-reinforced polymers are now being considered. Unidirectional or woven continuous fibres, made of glass, polyethylene, carbon or Kevlar, have been evaluated. This study focused on the use of glass fibre knitted fabrics to reinforce acrylate resins, in order to investigate the possibility to construct single crowns as well as three unit bridges. Some points affecting the final composite system were tested ; 1) static strength, with focus on the stress transfer under a occlusal contact point ; 2) modelling of a three nit bridge ; 3) fatigue strength as a posterior three unit bridge material. The study demonstrated that knitted fabric reinforcements are showing an interesting compromise between stiffness, static strength for single crown. For three unit bridge applications in the posterior arch, however knitted glass fabric reinforcements were not strong enough in fatigue An additional reinforcement in the posterior arch fixed partial denture design was recommended.

• Composites Research
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• 제14권4호
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• pp.8-14
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• 2001

위성체 시스템은 발사 과정중에 매우 극심한 하중상태에 놓이게 된다. 따라서 위성체 시스템의 구조적 안정성을 보장하기 위하여 발사 과정중에 시스템에 발생할 수 있는 모든 하중상태에 대해서 위성체 시스템 모든 부분의 안전율 (M.S. : Margin of Safety)는 양의 값이 되어야 한다. 본 논문은 위성체 안테나 시스템의 동적 특성을 분석하기 위하여 모드해석을 수행하였고, 준정적 하중이 시스템에 부과될 때 응력해석 결과를 나타내었다. 위성체 시스템 제작에 사용된 샌드 위치 구조물에 대한 파손경향을 조사하였고, 샌드위치 구조물의 외피를 일방향 프리프레그를 다양한 각도로 적층하여 구성하였을 때 시스템의 거동변화를 관찰하였다.

• 한국재료학회지
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• 제23권9호
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• pp.531-536
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• 2013

This paper investigates the effect of prolonged high temperature exposure on concentric laminated $Al_2O_3-ZrO_2$ composites. An ultrafine scale microstructure with a cellular 7 layer concentric lamination with unidirectional alignment was fabricated by a multi-pass extrusion method. Each laminate in the microstructure was $2-3{\mu}m$ thick. An alternate lamina was composed of 75%$Al_2O_3$-(25%m-$ZrO_2$) and t-$ZrO_2$ ceramics. The composite was sintered at $1500^{\circ}C$ and subjected to $1450^{\circ}C$ temperature for 24 hours to 72 hours. We investigated the effect of long time high temperature exposure on the generation of residual stress and grain growth and their effect on the overall stability of the composites. The residual stress development and its subsequent effect on the microstructure with the edge cracking behavior mechanism were investigated. The residual stress in the concentric laminated microstructure causes extensive micro cracks in the t-$ZrO_2$ layer, despite the very thin laminate thickness. The material properties like Vickers hardness and fracture toughness were measured and evaluated along with the microstructure of the composites with prolonged high temperature exposure.

• Structural Engineering and Mechanics
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• 제50권6호
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• pp.773-796
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• 2014

This paper deals with free vibration analysis of continuous grading fiber reinforced (CGFR) and bi-directional FG annular sector plates on two-parameter elastic foundations under various boundary conditions, based on the three-dimensional theory of elasticity. The plates with simply supported radial edges and arbitrary boundary conditions on their circular edges are considered. A semi-analytical approach composed of differential quadrature method (DQM) and series solution is adopted to solve the equations of motion. Some new results for the natural frequencies of the plate are prepared, which include the effects of elastic coefficients of foundation, boundary conditions, material and geometrical parameters. Results indicate that the non-dimensional natural frequency parameter of a functionally graded fiber volume fraction is larger than that of a discrete laminated and close to that of a 2-layer. It results that the CGFR plate attains natural frequency higher than those of traditional discretely laminated composite ones and this can be a benefit when higher stiffness of the plate is the goal and that is due to the reduction in spatial mismatch of material properties. Moreover, it is shown that a graded ceramic volume fraction in two directions has a higher capability to reduce the natural frequency than conventional one-dimensional functionally graded material. The multidirectional graded material can likely be designed according to the actual requirement and it is a potential alternative to the unidirectional functionally graded material. The new results can be used as benchmark solutions for future researches.

• Steel and Composite Structures
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• 제33권6호
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• pp.865-875
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• 2019

The current article proposed to develop a geometrical model for the analysis and modelling of the uniaxial functionally graded structure using the higher-order displacement kinematics with and without the presence of porosity including the distribution. Additionally, the formulation is capable of modelling three different kinds of grading patterns i.e., Power-law, sigmoid and exponential distribution of the individual constituents through the thickness direction. Also, the model includes the distribution of porosity (even and uneven kind) through the panel thickness. The structural governing equation of the porous graded structure is obtained (Hamilton's principle) and solved mathematically by means of the isoparametric finite element technique. Initially, the linear frequency parameters are obtained for different geometrical configuration via own computer code. The comparison and the corresponding convergence studies are performed for the unidirectional FG structure for the validation purpose. Finally, the impact of different influencing parameters like aspect ratio (O), thickness ratio (S), curvature ratio (R/h), porosity index (λ), type of porosity (even or uneven), power-law exponent (n), boundary condition on the free vibration characteristics are obtained for the FG panel and discussed in details.

• Composites Research
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• 제24권5호
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• pp.1-8
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• 2011

본 논문은 필라멘트 와인딩 압력용기의 섬유 강도 크기 효과에 관한 이론 해석 및 시험 결과를 제시하였다. 첫 번째로, 카본-에폭시로 필라멘트 와인딩된 여러 크기의 후프 링 시험을 수행한 결과 섬유 강도의 크기 효과가 현저하게 나타났다. 다음으로, 해석적 방법으로 와이블 최약 파손 모델과 다 단계 연속 파손 모델을 이용한 파손 해석을 수행하여 후프 링 시험 결과 및 다른 문헌의 한 방향 복합재 시험 결과와 비교하였다. 해석 결과는 시험 결과와 비교하여 현저하게 낮은 섬유 강도 값들을 나타내었다. 본 논문에서는, 길이 방향의 크기 효과를 변경한 개선형 다단계 연속 파손 이론을 제시하였다. 개선형 다단계 연속 파손 이론으로부터 구한 섬유 강도 값들은 시험 결과들과 좋은 일치를 보였다.

• 한국생산제조학회지
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• 제26권2호
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• pp.185-192
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• 2017

In this paper, we reviewed major design parameters for a solid type of deployable antenna and its structural design. We performed modal analysis for a single reflector panel made of aluminum and CFRP (carbon fiber reinforced plastic) to confirm the appropriateness of selected materials. We then predicted the elastic modulus of CFRP using the principles of unidirectional composite elasticity stiffness predictions such as the ROM (Rule of Mixture) and HSR (Hart Smith 10% Rule). To optimize the shape of the antenna reflector, a structural stiffness analysis was performed using derived numerical optimization factors. Six structural stiffness analyses were performed using the constructed experimental design method. The resulting optimal shape conditions are proposed to meet the structural stiffness requirements while minimizing weight.

• 한국분말재료학회지
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• 제27권3호
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• pp.193-197
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• 2020

Porous Cu-14 wt% Co with aligned pores is produced by a freeze drying and sintering process. Unidirectional freezing of camphene slurry with CuO-Co₃O₄ powders is conducted, and pores in the frozen specimens are generated by sublimation of the camphene crystals. The dried bodies are hydrogen-reduced at 500℃ and sintered at 800℃ for 1 h. The reduction behavior of the CuO-Co₃O₄ powder mixture is analyzed using a temperature-programmed reduction method in an Ar-10% H₂ atmosphere. The sintered bodies show large and aligned parallel pores in the camphene growth direction. In addition, small pores are distributed around the internal walls of the large pores. The size and fraction of the pores decrease as the amount of solid powder added to the slurry increases. The change in pore characteristics according to the amount of the mixed powder is interpreted to be due to the rearrangement and accumulation behavior of the solid particles in the freezing process of the slurry.