• Composites Research
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• v.31 no.6
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• pp.421-428
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• 2018

In order to optimize the prepreg compression molding (PCM) process, the forming simulation is required to cope with any problems that may be raised during the process. For the improvement of simulation accuracy, the input data of material property should be measured accurately. However, most studies assume that the compressive properties of the prepreg are identical to the tensile properties without quantifying them separately. Therefore, in this study, the in - plane compressive properties of the prepreg are presented to improve the accuracy of the forming simulation. As a result, the compressive modulus of the fibers was measured to be about $10^{-2}$ times lower than the tensile modulus. Also we designed a square-cup mold with a tilting angle of $110^{\circ}$ to simulate the prepreg formability during the high temperature compression mold process. Shear angles were measured at each corner, which were compared with the simulation results. It was observed that the simulation results using the accurate compressive properties of the prepreg showed a similar trend with the experimental results. It was confirmed that the measured data of the in-plane compression property improved the accuracy of the forming simulation results.

• Journal of the Korea Institute of Building Construction
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• v.19 no.2
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• pp.113-121
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• 2019

Single walled carbon nanotube (SWCNT) has been used as a material for reinforcing various advanced materials because it has superior mechanical properties. However, pure SWCNT that does not have any functional group has a hydrophobic character, and exists as bundles due to the strong Van der Waals attraction between each SWCNT. Due to these reasons, it is very difficult to disperse SWCNTs in the water. In this work, in order to use SWCNT for production of cementitious composites, SWCNT was first dispersed in water to make an aqueous solution. Sodium deoxycholate (DOC) and Sodium dodecyl sulfate (SDS) were chosen as surfactants, and the dosage of DOC and SDS were 2wt% and 1wt%, respectively. Sonication and ultracentrifugation were applied to separate each SWCNT and impurities. Using such processed SWCNT solutions, cement paste was prepared and its shear stress vs. strain rate relationship was studied. The yield stress and plastic viscosity of cement paste were obtained using Bingham model. According to the results in this work, cement pastes made with DOC and SDS showed similar rheological behavior to that of air entrained cement paste. While cement paste made with DOC 2 wt.% SWCNT solution showed similar rheological behavior to that of plain cement paste, cement paste made with SDS 1 wt.% SWCNT solution showed different rheological behavior showing much less yield stress than plain cement paste.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.2
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• pp.54-60
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• 2019

Recently, various composite materials for additive manufacturing are interested to expand the application field of 3D printing. 3D printing technique was mainly developed using polymer, and ceramic materials for 3D printing are still in the early stage of research due to the requirement of high solid content and post treatment process. In this study, silica particles with various diameters were surface treated with silane coupling agent, and synthesized as silica composite with photopolymer to apply DLP 3D printing process. DLP is an additive manufacturing technology, which has high accuracy and applicability of various composite materials. The rheological behavior of silica composite was analyzed with various solid contents. After DLP 3D printing was performed using silica composites, the printing accuracy of the 3D printed specimen was less than about 3 % to compare with digital data and he bending strength was 34.3 MPa at the solid content of 80 wt%.

• Composites Research
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• v.35 no.3
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• pp.147-152
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• 2022

Low-temperature characteristics according to internal temperature conditions during rotational molding of Type 4 pressure vessel liners were studied in this paper. Since rotational molding has a sensitive effect on the formability of the liner depending on the temperature conditions, the temperature conditions for the polyamide used should be accurately set. The structural changes of polyamide as the liner material was analyzed the surface by atomic force microscope (AFM), and the crystallinity measured with a differential scanning calorimeter (DSC) is used to evaluate the change of the mechanical strength value at low temperature. In addition, the formability of the liner was confirmed by observation of the yellow index inside the liner. As a result, as the melting range of the internal temperature becomes wider, the yellow index shows a lower value, and the elongation and impact characteristics at low temperatures are improved. It was also confirmed that the structure of the polyamide was uniform and the crystallinity was high by AFM and DSC. These experimental results contribute to the improvement of characteristics at low temperatures due to changes in temperature conditions during rotational molding.

• Composites Research
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• v.35 no.6
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• pp.378-393
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• 2022

As an emerging power generation technology, triboelectric nanogenerators (TENGs) have received increasing attention due to their boundless promise in energy harvesting and self-powered sensing applications. The recent rise of soft robotics has sparked widespread enthusiasm for developing flexible and soft sensors and actuators. TENGs have been regarded as promising power sources for driving actuators and self-powered sensors, providing a unique approach for the development of soft robots with soft sensors and actuators. In this review, TENG-based soft robots with different morphologies and different functions are introduced. Among them, the design of biomimetic soft robots that imitate the structure, surface morphology, material properties, and sensing/generating mechanisms of nature has greatly benefited in improving the performance of TENGs. In addition, various bionic soft robots have been well improved compared to previous driving methods due to the simple structure, self-powering characteristics, and tunable output of TENGs. Furthermore, we provide a comprehensive review of various studies within specific areas of TENG-enabled soft robotics applications. We first explore various recently developed TENG-based soft robots and a comparative analysis of various device structures, surface morphologies, and nature-inspired materials, and the resulting improvements in TENG performance. Various ubiquitous sensing principles and generation mechanisms used in nature and their analogous artificial TENG designs are demonstrated. Finally, biomimetic applications of TENG enabled in tactile displays as well as in wearable devices, artificial electronic skin and other devices are discussed. System designs, challenges and prospects of TENGs-based sensing and actuation devices in the practical application of soft robotics are analyzed.

• Composites Research
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• v.35 no.6
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• pp.447-455
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• 2022

Currently, the problem of pollution of the marine environment by microplastics is emerging seriously internationally. In this study, to develop a lightweight portable microplastic collection device, the types and number of microplastics in 21 coastal areas nationwide in Korea were investigated. And CFRP (Carbon Fiber Reinforced Plastic), GFRP (Glass Fiber Reinforced Plastic), ABS (Acrylonitrile Butadiene Styrene copolymer) and aluminum were applied for design and analysis of microplastic collection device to have the durability, corrosion resistance and lightweight. As a result of sample collection and classification from the shore, it was confirmed that microplastics were distributed the most in Hamdeok beach, and the polystyrene was found to be mainly distributed microplastics. Particle information through coastal field survey and CFD (Computational Fluid Dynamics) analysis were used to analyze the flow rate and distribution of particles such as sand and impurities, which were applied to the structural analysis of the cyclone device using the finite element method. As a result of structural analysis considering the particle impact inside the cyclone device, the structural safety was examined as remarkable in the order of CFRP, GFRP, aluminum, and ABS. In the view of weight reduction, CFRP could be reduced in weight by 53%, GFRP by 47%, and ABS by 61% compared to aluminum for the cyclone device.

• Composites Research
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• v.35 no.5
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• pp.347-358
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• 2022

Carbon fiber is an excellent structural material, which has been proven in many industries, and the shipbuilding industry is no exception. In particular, in advanced maritime countries, special ships of the Navy and Coast Guard with carbon fiber composite hulls have already been deployed. In Korea, carbon fiber composite materials have been applied to a 10-ton class leisure craft or a 30-ton class patrol, but no research has been done on a hundred of tons or more vessels. In this study, the feasibility study of a 500-ton patrol vessel with a carbon fiber composite hull was conducted through an analysis of similar cases abroad. As a result, it was recognized that the developed hull can be reduced in weight by about 21% to 25% compared to the existing aluminum or FRP hull. It was also confirmed that this light-weight effect can induce the improvement of the maximum speed and the improvement of the operating range via simulations.

• Composites Research
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• v.36 no.1
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• pp.16-24
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• 2023

This paper presents a multi-scale progressive fatigue damage model incorporating the model for interfacial debonding between fibers and matrix. The micromechanics model for the progressive interface debonding was adopted, which defined the four different interface phases: (1) perfectly bonded fibers; (2) mild imperfect interface; (3) severe imperfect interface; and (4) completely debonded fibers. As the number of cycles increases, the progressive transition from the perfectly bonded state to the completely debonded fiber state occurs. Eshelby's tensor for each imperfect state is calculated by the linear spring model for a damaged interface, and effective elastic properties are obtained using the multi-phase homogenization method. The fatigue damage evolution formulas for fiber, matrix and interface were proposed to demonstrate the fatigue behavior of CFRP laminates under cyclic loading. The material parameters for the fiber/matrix fatigue damage were characterized using the chaotic firefly algorithm. The model was implemented into the UMAT subroutine of ABAQUS, and successfully validated with flat-bar UD laminate specimens ([0]₈,[90]₈, [30]₁₆) of AS4/3501-6 graphite/epoxy composite.

• Korean Chemical Engineering Research
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• v.61 no.1
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• pp.32-38
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• 2023

In this study, the electrochemical properties of dopamine coated silicon/silicon carbide/carbon(Si/SiC/C) composite materials were investigated to improve cycle stability and rate performance of silicon-based anode active material for lithium-ion batteries. After synthesizing CTAB/SiO₂ using the Stöber method, the Si/SiC composites were prepared through the magnesium thermal reduction method with NaCl as heat absorbent. Then, carbon coated Si/SiC anode materials were synthesized through polymerization of dopamine. The physical properties of the prepared Si/SiC/C anode materials were analyzed by SEM, TEM, XRD and BET. Also the electrochemical performance were investigated by cycle stability, rate performance, cyclic voltammetry and EIS test of lithium-ion batteries in 1 M LiPF₆ (EC: DEC = 1:1 vol%) electrolyte. The prepared 1-Si/SiC showed a discharge capacity of 633 mAh/g and 1-Si/SiC/C had a discharge capacity of 877 mAh/g at 0.1 C after 100 cycles. Therefore, it was confirmed that cycle stability was improved through dopamine coating. In addition, the anode materials were obtain a high capacity of 576 mAh/g at 5 C and a capacity recovery of 99.9% at 0.1 C/0.1 C.

• Composites Research
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• v.21 no.6
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• pp.8-14
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• 2008

Lighting system of road is an essential structure used for the safety of pedestrians and vehicles. Most of the lighting pole is made with steel which is vulnerable under corrosive environment. To overcome such corrosion problems, stainless steel and iron steel are used, but they are usually manufactured by hand which is not efficient. Due to their high strength and stiffness, when there is car collision with the lighting pole structure the safety of driver may not be ensured. Hence, the development of new-type lighting pole system which is easy to adjust the right on the road, lengthen the service life, and reduce the maintenance, is necessary. Lighting pole made with aluminum alloy is high in strength per unit weight, is strong against corrosive environment, and is easy to construct due to flexibility and right weight. But, because the strength and stiffness of the material is lower than that of steel, the structural safety and serviceability of the system can be a problem. To mitigate the structural problem associated with conventional lighting pole system, experimental investigation is conducted on the conventional lighting pole and rib reinforced aluminum alloy lighting pole, respectively. By comparison of results, it was found that the rib reinforced Mg-Si aluminum alloy lighting pole is efficiently applicable to the lighting pole system of road.