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김종현,권동준,박종만,K. Lawrence DeVries 한국섬유공학회 2022 Fibers and polymers Vol.23 No.11
Adhesion of hybrid composite materials is essential in the manufacture of wind turbine blades. In the case of huge composite structures, however, the adhesive section between hybrid composite (GFRP, CFRP) was too thick, and it could be lead to decrease adhesion peroperty. In this research, adhesive properties were investigated with different adhesive thicknesses for glass fiber and carbon fiber reinforced hybrid composites. As the adhesive thickness increased, the lap shear strength (LSS) decreased in a rather exponential function. In addition, there were problems that as the thickness of the adhesive increases, voids easily formed inside the adhesive, and the thick adhesive layer had low resistance to bending. Even when the thick bonding section was formed with GFRP addition, added GFRP was deformed more in the bonding part upon the applied external stress. This could be because the interfacial stress was greater than that of the neat epoxy adhesive. It was monitored by 3D electrical resistance (ER) mapping of the CFRP substrate was used to evaluate the shear stress transfer of the bonding part and the CFRP substrate. The addition of GFRP to the epoxy adhesive can improve the adhesion and the resistance to shear failure for thick adhesive parts, such as wind turbine blades (WTB).
백영민,신평수,김종현,박하승,K. Lawrence DeVries,박종만 한국섬유공학회 2019 Fibers and polymers Vol.20 No.11
Currently, continuous polymer fibers are usually manufactured in versatile forms such as, aramid fiber. In thisstudy, continuous polycarbonate (PC) fiber having the uniform diameter was manufactured from a thermoplastic PC resinusing a twin screw extruder. Carbon nanotubes (CNTs) were uniformly dispersed in the PC resin, using a solvent dispersionmethod. The effect of CNT on the mechanical properties of PC fiber was analyzed statistically, using Weibull distribution, bysingle PC fiber tensile test. Dynamic contact angle was measured to compare the surface energies of PC fiber and PC-CNTfiber on the water droplet. The difference in the wetting patterns was also observed by injecting a solvent between two fibers. Tensile strength and Young’s modulus of the PC fiber was significantly increased by the addition of even a small amount ofCNT. This improvement can be attributed to the excellent reinforcing and stress transferring effects of the CNT filler. Composites were made of both types of PC film and PC fiber as a matrix and their impregnation properties were investigatedby inspection of photographs of their cross-sections. The mechanical properties of the two-types of composites were alsocompared by tensile testing. From the cross-sectional fractography and the permeated PC weight, PC fiber type exhibitedbetter impregnation property than the PC film type, and thus resulted in the improved tensile strength.
Jong-Hyun Kim,권동준,K. Lawrence DeVries,Joung-ManPark 한국섬유공학회 2022 Fibers and polymers Vol.23 No.6
This study improved the interfacial and mechanical properties of carbon fiber (CF) reinforced 5-ethylidene-2-norbornene (ENB) composites using the Ru catalyst coating method on CF for vacuum-assisted resin transfer molding(VARTM). Generally, the Ru catalyst added ENB was polymerized using mixing two materials. The interfacial andmechanical properties of the composites containing Ru catalyst coated carbon fabric were higher than those in which Rucatalyst was mixed in the ENB before being embedded in the CF fabric. It can be mainly due to the uniform or randomdispersion of Ru catalyst by two different manufacturing processes. The interfacial properties determined using themicrodroplet test, e.g., the surface energy and work of adhesion, Wa, were consistent with macro-mechanical properties. Fromthe T-peel test combined with electrical resistance (ER), the Ru catalyst coated CF fabric/ENB composite respondedreasonably well with high peeling strength. The different Ru catalyst processing methods resulted in different interfacial,mechanical, and electrical sensing properties, with the Ru catalyst coated CF composites typically having better properties. This study is about the Ru catalyst coated CF fabric, which can be applied to manufacture geometrically complex and largestructural composites and will help improve product manufacturing efficiency and quality.
박하승,신평수,김종현,백영민,권동준,이우일,K. Lawrence DeVries,박종만 한국섬유공학회 2018 Fibers and polymers Vol.19 No.9
Recently new poly-dicyclopentadiene (p-DCPD) has increasing been used for composites in military, aerospace, and transportation applications due to its favorable impact properties. In this work, the cross-linking density of p-DCPD with different post curing conditions was indirectly measured by thermal analysis using differential scanning calorimetry (DSC), weight variation accompanying swelling and density. The effects of the post curing conditions on mechanical properties of p- DCPD and glass fiber (GF)/p-DCPD were determined via tensile, Izod impact, and flexural tests at ambient and low temperatures (-20 oC). Interfacial properties were evaluated by fragmentation and cyclic loading tests. The work of adhesion was determined via Static contact angle using four solvents measurements, to provide the information on the differences in the interfacial properties between GF and p-DCPD. The change of cross-linking density by post curing of p-DCPD affected the mechanical and interfacial properties of GF/p-DCPD composites.
백영민,신평수,김종현,박하승,권동준,K. Lawrence DeVries,박종만 한국섬유공학회 2018 Fibers and polymers Vol.19 No.8
The mechanical and interfacial properties were evaluated for carbon fiber reinforced composites (CFRC) manufactured using thermally recycled waste carbon fiber and recycled polyethylene terephthalate (PET). The mechanical properties of the recycled fiber were determined and compared to those of neat fibers using the single-fiber tensile test. The surfaces of the recycled and neat carbon fiber were examined and compared using FE-SEM and dynamic contact angle measurements. A goal of the study was to determine the applicability of industrial use of recycled CF and/or recycled PET in CFRC. Mechanical properties were measured using short beam and tensile tests. These properties were observed to be correlated with crystallinity. The interfacial properties between the recycled carbon fibers and recycled PET were evaluated using the microdroplet test. At low temperature residual resin remained on the recycled CFs surface resulting relatively the low interfacial properties. At excessively high temperatures, oxidation occurred, on the CFs surface, which also resulting in relatively poor low mechanical properties. The optimal treatment condition was 500 oC, where the surface was relatively clean and the reduction in mechanical properties was minimized.
Ha-Seung Park,Pyeong-Su Shin,Jong-Hyun Kim,백영민,K. Lawrence DeVries,Joung-ManPark 한국섬유공학회 2020 Fibers and polymers Vol.21 No.7
This paper describes a new type of sensor that can monitor electrical signals for external stress or damage and heattransfer. It is composed of conductive pencil lead graphite, which is sensitive, affordable and easy-to-handle. This work wasto detect mechanical damages in composites using Pencil Lead Drawn Paper Sensor (PLDPS). To measure electricalresistance (ER) via bending, by narrowing the distance between glass plates attached with PLDPD, ER increased stepwisewhile ER decreased with widening the distance reversely. The PLDPS can easily change the shape in a rectangular vortex. ER change responded well in tensile and flexural tests, while it showed leveling off under cyclic compression. TwodimensionalER mapping was used during impact, drilling and heat transfer tests for detecting damage and thermal transfer. Compared to strain gauges, PLDPS can be applied inexpensively to detect damages successfully under various mechanicaltests.
Kwon, Dong-Jun,Choi, Jin-Yeong,Shin, Pyeong-Su,DeVries, K. Lawrence,Park, Joung-Man Taylor Francis 2016 ADVANCED COMPOSITE MATERIALS -ZEIST- Vol.25 No.6
<P>Dispersion and shape of nanoparticles, as well as interfacial conditions, add significantly to difficulties in composite manufacture. In the work reported here, an innovative method of recycling composites using out-of-date prepreg was investigated in which the carbon nanotube (CNT) on the prepreg was optimally coated. Nanocomposites utilizing the out-of-date prepreg were coated with CNT and fabricated by a sheet molding method. CNT nanofillers were observed to be uniformly dispersed on epoxy prepreg by spray coating. The mechanical and interfacial properties of these CNT coated nanocomposites were improved over those of more conventionally manufactured carbon fiber/epoxy composites. The CNT nanofillers were embedded at the epoxy and fiber interface, as a result of etching of the epoxy prepreg surface by a CNT dispersion solution which enhanced interfacial reactivity.</P>
신평수,Jong-Hyun Kim,Ha-Seung Park,백영민,이상일,K. Lawrence DeVries,박종만 한국섬유공학회 2020 Fibers and polymers Vol.21 No.2
Composites has been an area of active research for the past several decades due to their lightweight and good mechanical properties. However, the aging of fiber reinforced composites is a major issue due to exposure of thermal, waterand ultraviolet conditions. Continuous damage could bring about mechanical property degradation and damage at the interface. This is a comprehensive review on of aging effects in water, heat, ultraviolet etc. on composites and the changes in chemical, mechanical and interfacial properties, evaluated by nondestructive and micro-mechanic evaluations. It focuses particularly on composites with superior chemical, mechanical and interfacial properties, as well as good high resistance to aging, as these are considered to be important Structural materials. Types of composites and aging effects of aged composite by exposure to water, heat and ultraviolet radiation are explored. Based on these nondestructive and micro-mechanical evaluations methods are suggested to reduce the diverse ageing effects.
Ha-Seung Park,Pyeong-Su Shin,Jong-Hyun Kim,백영민,K. Lawrence DeVries,Joung-ManPark 한국섬유공학회 2020 Fibers and polymers Vol.21 No.7
A study was performed to utilize Pencil Lead Drawn Paper Sensor (PLDPS) as a strain and damage sensor bydrawing multiply Pencil Sensors on two paper types. To evaluate the optimal paper as a PLDPS substrate of two type papers,i.e., plain and Han papers were used. The stability and uniformity of the mechanical properties, were compared for the papertypes. Variability of electrical resistivity (ER) was also determined using four different types of pencil lead to make thePLDPS. In the evaluation of the properties of the PLDPS, for the different pencil lead types, the pencil lead weight wasdetermined by drawing multiple lines and the ER of neat pencil leads and PLDPS compared. Interfacial properties of thePLDPS with different pencil lead types were measured by a spreading test, which provides information on wetting andpermeability properties, using double distilled water. The sensitivity and uniformity of the pencil lead paper sensors made offour different pencil leads were compared in tensile loading. Plain paper was more suitable than Han Paper for use as thesubstrate of PLDPS. In addition, compared to other pencil leads, 6B, which exhibited low sensitivity but high uniformity, wasdetermined to be the most suitable pencil lead.