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섬유부피분율 증가와 공극 감소를 위한 VARTM 공정의 대기압 제어에 관한 연구
곽성훈 ( Seong-hun Kwak ),김태준 ( Tae-jun Kim ),탁윤학 ( Yun-hak Tak ),권성일 ( Sung-il Kwon ),이재현 ( Jea-hyun Lee ),김상용 ( Sang-yong Kim ),이종천 ( Jong-cheon Lee ) 한국복합재료학회 2021 Composites research Vol.34 No.2
VARTM(Vacuum-assisted resin transfer molding) 공정은 OoA(Out of Autoclave)에 속하는 저가형 공정기술로 다양한 분야에 널리 사용되어 왔다. 그러나 오토클레이브 공정보다 품질이 낮아 고신뢰성이 요구되는 항공산업에는 적용하기 어려웠다. VARTM 공정의 주요 문제는 오토클레이브 대비 낮은 섬유부피분율과 높은 Void 함량에 의한 기계적 물성의 손실이었다. 따라서 많은 연구자들이 Void를 줄이고 섬유부피분율을 높일 수 있는 연구를 수행해 왔다. 이러한 연구의 흐름에 따라 본 연구에서는 수지 주입 과정 중 대기압을 제어하는 방법이 섬유부피분율을 높이고 Void를 감소시킬 수 있는지 검토하였다. 신뢰성 평가는 Void와 연관성이 있는 압축강도시험, 섬유부피분율 분석, 광학현미경 촬영을 통해 확인하였다. 결과적으로 VARTM 공정에서 수지 주입과정 중 대기압을 단계별로 높이는 방법이 섬유부피분율 증가와 Void 감소에 직접적인 효과가 있음을 확인하였다. VARTM (Vacuum-assisted resin transfer molding) process is a low-cost process technology and affiliated with OoA (Out of Autoclave). Besides, it has been widely used in various fields. However, because of its lower quality than the autoclave process, it isn't easy to apply the VARTM process to the aerospace industry, which requires high reliability. The main problem of the VARTM process is the loss of mechanical properties due to the low fiber volume fraction and high void content in comparison to the autoclave. Therefore, many researchers have studied to reduce void and increase fiber volume fraction. This study examines whether the method of controlling atmospheric pressure could increase the fiber volume fraction and reduce void during the resin impregnation process. Reliability evaluation was confirmed by compressive strength test, fiber volume fraction analysis, and optical microscopy. As a result, it was confirmed that increasing the atmospheric pressure step by step in the VARTM process of impregnating the preform with resin effectively increases the fiber volume fraction and reduces void.
Study on the unidirectional compaction of terminal cables in the CICC joint
남현일,이호진,박재학,홍계원 한국초전도학회 2002 Progress in superconductivity Vol.3 No.2
The void volume fraction of cables is one of the effective parameters to characterize the joints of superconducting magnet. Because electrical resistance and cooling stability in the CICC (Cable-in-Conduit Conductors) joint are governed by the void volume fraction, it should be controlled constantly in the termination of cable. The change of cross-section shape in the cable was fecund during the unidirectional compaction of terminal sleeve. The non-uniform thickness of the sleeve after compaction is expected because the loading is not taxi-symmetric, and the plastic flow is also not axi-symmetric. The CICC was compacted from 45% void volume fraction to 15% by using two-piece compaction jig, which could be pressed mini-directionally. Commercial code, ABAQUS, was used to analyze the plastic flow in the sleeve during the unidirectional compaction. The increment of radius of curvature of compaction jig could minimize the change of the deformed shape of cables. The calculated results were agreed with the experimental observations.
일축 압축하중 하 다공성 폴리우레탄폼의 재료비선형 거동 및 미세구조 변화
이은선,고태식,이치승,Lee, Eun Sun,Goh, Tae Sik,Lee, Chi-Seung 한국재료학회 2017 한국재료학회지 Vol.27 No.12
Porous materials such as polymeric foam are widely adopted in engineering and biomedical fields. Porous materials often exhibit complex nonlinear behaviors and are sensitive to material and environmental factors including cell size and shape, amount of porosity, and temperature, which are influenced by the type of base materials, reinforcements, method of fabrication, etc. Hence, the material characteristics of porous materials such as compressive stress-strain behavior and void volume fraction according to aforementioned factors should be precisely identified. In this study, unconfined uniaxial compressive test for two types of closed-cell structure polyurethane foam, namely, 0.16 and $0.32g/cm^3$ of densities were carried out. In addition, the void volume fraction of three different domains, namely, center, surface and buckling regions under various compressive strains (10 %, 30 %, 50 % and 70 %) were quantitatively observed using Micro 3D Computed Tomography(micro-CT) scanning system. Based on the experimental results, the relationship between compressive strain and void volume fraction with respect to cell size, density and boundary condition were investigated.
전기저항 측정을 통한 재료의 소성 변형시의 연속적 공극 체적 분율 측정에 관한 연구
안준영(Jun-Young Ahn),장택진(Taek-Jin Jang),이성진(Sung-Jin Lee),윤경재(Kyung Jae Yun),김종봉(Jong-Bong Kim) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
The tensile test is widely used to predict the hardening and fracture behavior of materials. But it cannot predict the accurate fracture behavior generated by the effect of microstructures such as void growth and coalescence. In this study, the electrical resistance during tensile test was measured and the actual cross-sectional area of materials without void is calculated to predict fracture behavior more precisely. The measured resistance was compared with the resistance calculated using the volume constancy assumption. Moreover, the evolutionary volume fraction without void was derived by using the measured electrical resistance. Finally, the evolutionary void volume fraction could be calculated.
Maruyama, Toshio,Ueda, Mitsutoshi The Korean Ceramic Society 2010 한국세라믹학회지 Vol.47 No.1
When metal oxides are exposed to chemical potential gradients, ions are driven to diffusive mass transport. During this transport process, the divergence of ionic fluxes offers the formation/annihilation of oxides. Therefore, the divergence of ionic flux may play an important role in the void formation in oxides. Kinetic equations were derived for describing chemical potential distribution, ionic fluxes and their divergence in oxides. The divergence was found to be the measure of void formation. Defect chemistry in scales is directly related to the sign of divergence and gives an indication of the void formation behavior. The quantitative estimation on the void formation was successfully applied to a growing magnetite scale in high temperature oxidation of iron at 823 K.
Toshio Maruyama,Mitsutoshi Ueda 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.1
When metal oxides are exposed to chemical potential gradients, ions are driven to diffusive mass transport. During this transport process, the divergence of ionic fluxes offers the formation/annihilation of oxides. Therefore, the divergence of ionic flux may play an important role in the void formation in oxides. Kinetic equations were derived for describing chemical potential distribution, ionic fluxes and their divergence in oxides. The divergence was found to be the measure of void formation. Defect chemistry in scales is directly related to the sign of divergence and gives an indication of the void formation behavior. The quantitative estimation on the void formation was successfully applied to a growing magnetite scale in high temperature oxidation of iron at 823 K.
Suhas Badakere Gopalakrishna,Chidanand Kishor Mangrulkar,Kiran Kumar Kapse Umashankar,Sathyabhama Alangar 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.4
The subcooled flow boiling (SFB) of a water-ethanol mixture are relevant in operating heat-dissipating devices, such as smaller catalytic reactors, electronic apparatus, and hybrid electric vehicle battery components. The operative temperature should always be at a sustainable value to evade the failure or breakdown of these heat-dissipating devices. To cool these devices, a water-ethanol mixture is used as a coolant. The forced convective as well as SFB heat transfer coefficients (HTCs) for the water-ethanol mixture are estimated numerically using the volume of fluid method in a rectangular channel with dimensions of 15 mm×15 mm× 150 mm. During SFB, the liquid-vapor interaction is examined by solving the bubble void fraction (BVF). For the discretization process, the Crank-Nicholson implicit method (scheme) is used, and the convective equation for the BVF is converted to an algebraic equation. The corrector predictor equation procedure is used for solving the BVF. The thermodynamic and thermophysical parameters related to subcooled boiling are estimated upon the incorporation of the bubble void fraction (α) using the mixture rule. These parameters are then incorporated into the x-momentum equation as well as into the energy equation for finding the fluid temperature, velocity, and pressure drop values. From the estimated values of temperature, subcooled flow boiling HTC is obtained. The estimated values of HTC can predict well compared with that of empirical equations. Moreover, mass flux plays a vital role in the forced convective region, while heat flux has a crucial role in the SFB region for the improvement of HTC.
Carlos Andres Espinosa Dominguez,Honorio Ortiz Hernández,Helvio Mollinedo,Orlando Susarrey Huerta,Hilario Hernández Moreno 한국고분자학회 2023 폴리머 Vol.47 No.1
The manufacturing process of composite materials is crucial in determining their final quality and mechanical and physical properties. Although manufacturing defects affecting mechanical properties cannot be entirely eliminated, some process parameters can be improved to reduce them, and solutions without increasing manufacturing costs are sought. Currently, research on aramid fibers and epoxy resin is booming; thus, this study aims to apply the vacuum bag process with epoxy matrix and aramid fiber reinforcement, focusing on the manufacturing process parameters. Herein, a procedure for the hand lay-up of aramid impregnated with resin and the vacuum bag method for a composite laminate is described. Some variations and improvements in the vacuum bag technique were applied, improving the breathable layers in the mold to enhance the extraction of gases and promote a homogenous pressure distribution. ASTM procedures were performed to obtain the density and constituent content of the composite material, resulting in a fiber volume fraction of 0.606, a resin volume fraction of 0.294, and a porosity volume fraction of 0.098.