• Composites Research
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• v.32 no.3
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• pp.148-157
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• 2019

In this study, $C_f/SiC$, $SiC_f/SiC$ and $C_f-SiC_f/SiC$ ceramic composites reinforcing carbon fiber, SiC fiber and hybrid fiber were fabricated by hybrid TGCVI and PIP process. After the thermal shock cycle, 3-point bending and Oxy-Acetylene torch test, their mechanical behavior, oxidation and erosion resistance were evaluated. The $C_f/SiC$ composite showed a decrease in mechanical property along with increasing temperature, a pseudo-ductile fracture mode and a large quantity of erosion. The $SiC_f/SiC$ composite exhibited stronger mechanical property and lower erosion rate compared to the $C_f/SiC$, but brittle fracture mode. On the other hand, hybrid type of $C_f-SiC_f/SiC$ composite gave the best mechanical property, more ductile failure mode than the $SiC_f/SiC$, and lower erosion rate than the $C_f/SiC$. During the Oxy-Acetylene torch test, the $SiO_2$ formed by reaction of the SiC matrix with oxygen prevented further oxidation or erosion of the fibers for $C_f-SiC_f/SiC$ and $SiC_f/SiC$ composites particularly. In conclusion, if a hybrid composite with low porosity is prepared, this material is expected to have high applicability as a high temperature thermo-structural composite under high temperature oxidation atmosphere by improving low mechanical property due to the oxidation of $C_f/SiC$ and brittle fracture mode of $SiC_f/SiC$ composite.

• Korean Journal of Heritage: History & Science
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• v.39
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• pp.243-280
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• 2006

At the Bujang-ri Site, Seosan, South Chungcheong Province, around 220 archaeological features, including semi-subterranean houses and pits of Bronze Age and semi-subterranean houses, pits, and burials of Baekje period had been identified and investigated. In Particular, mound burials No. 5 of 13 of Baekje mound burials yielding a gilt-bronze cap along with other valuable artifacts drew international scholarly attention. The gilt-bronze cap from the mound burial No. 5 is a significant archaeological data not only in the study of Baekje archaeology but also in the study of international affairs and exchange at that time. At the time of exposure, the gilt-bronze cap was already broken into a number of pieces and seriously damaged by corrosion, and hardening and urethane foam were necessary in the process of collecting its pieces. Ahead of main conservational treatments on cap, X-ray photograph and CT(computerizes tomography) were taken in order to examine interior structure of the cap and to decide appropriate treatments. In the five layers identified in the profile of cap, a textile layer was set between a metal and a layerof bark of paper birch for avoiding direct contact of the metal and the bark of paper birch. Analyses were executed for examining textile layer and a layer of fibroid material. According to microscopic analysis, while the textile layer consisted of the simplest plain fabric with one fold among three kinds of textile structures, the layer of fibroid material was mixed with two or three kinds of fibers. A comparative analysis with standard sample using FT-IR (Fourier Transform Infrared Spectroscopy) announced that both textiles and fabrics were hemp. Analysis of kind of the paper birch resulted in barks of paper birch with 15 fold. A metallographic microscope, SEM, and WDS were used for the analysis of microscopic structures of plated metal pieces. While amalgam plating was treated as a plating method, the thickness of the plated layer, a barometer of plating technique, was ranged from $1.72{\mu}m$ to $8.67{\mu}m$. The degree of purity of gold (Au) used in plating was 98% in average, and less than 1% of silver (Ag) was included.

• Science of Emotion and Sensibility
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• v.24 no.1
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• pp.105-114
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• 2021

This study determines the differences between Korean female university students and their Chinese counterparts residing in Korea by evaluating the subjective sensation and tactile preference in fabrics for casual shirts. Seven types of white causal shirt fabrics were selected as specimens from those available in spring and autumn shirt collection. The fabrics were made from various fibers (cotton 100%, polyester 100%, flax 100%, polyester 80%/cotton 20%, polyester 65%/cotton 35%, polyester 50%/cotton 45%/spandex 5%, and polyester 50%/modal 50%). Forty Korean and Chinese female university students subjectively assessed the subjective sensation of fabrics used for casual shirts. Participants were asked to observe the seven types of fabrics and complete the questionnaire. The subjective sensation to be assessed for white casual shirt fabrics was classified into the following four factors: smoothness, lightness, softness, and stretchiness. Subjective sensation factors showed partially significant differences by nationality. Korean female students evaluated cotton fabric as being light, whereas their Chinese counterparts evaluated the polyester/cotton/spandex blended fabric as light. Korean female students evaluated polyester/modal blended fabric as being stretchable. The tactile preference for fiber composition of the fabrics showed partially significant differences by nationality. Korean female students preferred cotton 80%/polyester 20% blended fabric, polyester 50%/cotton 45%/spandex 5% blended fabric, and flax 100% fabric. The subjective sensation of the fabrics had different effects on preferences by nationality. Smoothness and softness had positive effects on preferences for the fabrics of Korean students. However, smoothness, softness, and stretchiness had positive effects on the preferences of Chinese students. The subjective sensation and tactile preference for casual shirt fabrics showed a difference between Korean female students and their Chinese counterparts. Therefore, when planning casual shirt fabrics for female university students, it is necessary to reflect on these differences in subjective sensation and tactile preference.

• Korean Journal of Environment and Ecology
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• v.35 no.3
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• pp.256-264
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• 2021

Rapid urbanization around the world has negatively affected wildlife habitats, including birds. Wild birds settled in the city are adapting to the changed surroundings, and are typically known to make nests using materials that are easy to find around the city. This study was conducted for the purpose of analyzing the nesting materials on the Paridae using artificial bird nests installed in cities. In this study, the researchers established a total of 33 artificial bird nests in urban parks (22) and forests (11) in Cheonan-si, Chungcheongnam-do. Then we collected 4 artificial bird nests in urban parks (18.19%) and 5 in urban forests (45.46%) to compare the characteristics of bird nest materials by the nest, species, and urban green area types. Eight nests, excluding a nest abandoned by a pair of Paridae, were used for the material analysis. The collected nests were dried, and classified into natural materials (vegetable materials, animal materials, moss, and soil) and artificial materials (cotton, paper pieces, plastics, vinyl, and synthetic fibers), and then each nest was weighed. The classification result shows that the portion of moss (50.65%) was the highest in all nests, followed by soil (21.43%), artificial material (13.95%), vegetable material (5.78%), animal material (4.57%), and others (3.59%) in that order. Artificial materials were used in all nests in urban green areas. Moreover, although the Paridae used about 5.16% more vegetable material than the Parus varius, it was not significant (t=2.17, p=0.07). Plant materials and soil were most preferred in urban forests, and moss, animal, and artificial materials were widely used in that order in urban parks. There was a significant difference in the use of vegetable materials between urban parks and urban forests (t=3.07, p<0.05^*). In the habitats like urbanized and dry areas, where artificial materials are highly accessible, artificial materials replaced some roles of natural materials. This study is a basic study for the analysis of the types of materials used in artificial bird nests to understand the habitat system of urban ecosystems. It can be used as the basic data for ecological studies and conservation of the Paridae species.

• Composites Research
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• v.34 no.4
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• pp.241-248
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• 2021

As the electric vehicle market grows, there is an issue of light weight vehicles to increase battery efficiency. Therefore, it is going to replace the battery module cover that protects the battery module of electric vehicles with high strength/high heat-resistant polymer composite material which has lighter weight from existing aluminum materials. It also aims to respond to the early electric vehicle market where technology changes quickly by combining 3D printing technology that is advantageous for small production of multiple varieties without restrictions on complex shapes. Based on the composite material mechanics, the critical length of glass fibers in short glass fiber (GF)/polycarbonate (PC) composite materials manufactured through extruder was derived as 453.87 ㎛, and the side feeding method was adopted to improve the residual fiber length from 365.87 ㎛ and to increase a dispersibility. Thus, the optimal properties of tensile strength 135 MPa and Young's modulus 7.8 MPa were implemented as GF/PC composite materials containing 30 wt% of GF. In addition, the filament extrusion conditions (temperature, extrusion speed) were optimized to meet the commercial filament specification of 1.75 mm thickness and 0.05 mm standard deviation. Through manufactured filaments, 3D printing process conditions (temperature, printing speed) were optimized by multi-optimization that minimize porosity, maximize tensile strength, and printing speed to increase the productivity. Through this procedure, tensile strength and elastic modulus were improved 11%, 56% respectively. Also, by post-processing, tensile strength and Young's modulus were improved 5%, 18% respectively. Lastly, using the FEA (finite element analysis) technique, the structure of the battery module cover was optimized to meet the mechanical shock test criteria of the electric vehicle battery module cover (ISO-12405), and it is satisfied the battery cover mechanical shock test while achieving 37% lighter weight compared to aluminum battery module cover. Based on this research, it is expected that 3D printing technology of polymer composite materials can be used in various fields in the future.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.67 no.3
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• pp.172-179
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• 2022

Sweet potato varieties with high fiber content in the storage root have poor texture when steamed or roasted. This study investigates the difference in fiber content among sweet potato varieties by soil and climate. The average fiber content of 'Hogammi', 'Sodammi', 'Pungwonmi', 'Danjami', and 'Jinyulmi' cultivars from the samples collected at farms in Haenam, Muan, and Unbong, Korea were 95.71, 66.73, 44.55, 40.55, and 38.53 mg/100g FW, respectively. There was no significant difference between site-specific conditions and varieties. Based on the degree of visual fibrousness, 'Hogammi' has an average of 3.6-4.0 with many thick stringy fibers. The fiber content of the 'Hogammi' cultivar was measured across 19 sites representing the main sweet potato growing regions of Korea. The fiber content was between 115.82 and 114.6 mg/100g in Haenam 2 and Boryeong 1, and 87.46 mg/100g in Hamyang. However, the fiber content at the remaining 16 sites was within the range of 94.63-108.52 mg/100g, although there were some site-level differences. The fiber content of the sweet potato storage roots were positively correlated with soil phosphorus (R² = 0.58^**), organic matter (R² = 0.52^*), and pH (R² = 0.51^*), which had a significance of 1% and 5%. The fiber content of sweet potato storage roots was found to have increased with increasing phosphorus content, organic matter and pH in the soil. However, there was no correlation with the amount of precipitation, days of precipitation and hours of sunshine with the fiber content of sweet potato at the selected sites.

• Journal of Wetlands Research
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• v.24 no.2
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• pp.83-92
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• 2022

The amount of the plastic waste has been increasing according to global demand for plastic. Microplastics are the most hazardous among all plastic pollutants due to their toxicity and unknown physicochemical properties. This study investigates the optimal methodology that can be applied to sewage samples for detecting microplastics before discussing reducing microplastics in MWTPs. In this study, the effect of different pretreatment methods while detecting microplastic analysis of MWTP influent samples was investigated; the samples were collected from the J sewage treatment plant. There are many pretreatment methods but two of them are widely used: Fenton digestion and hydrogen peroxide oxidation. Although there are many pretreatment methods that can be applied to investigate microplastics, the most widely used methods for sewage treatment plant samples are Fenton digestion and H₂O₂ oxidation. For each pretreatment method, there were factors that could cause an error in the measurement. To overcome this, in the case of the Fenton digestion pretreatment, it is recommended to proceed with the analysis by filtration instead of the density separation method. In the case of the H₂O₂ oxidation method, the process of washing with distilled water after the reaction is recommended. As a result of the analysis, the concentration of microplastics was measured to be 2.75ea/L for the sample using the H₂O₂ oxidation method and 3.2ea/L for the sample using the Fenton oxidation method, and most of them were present in the form of fibers. In addition, it is difficult to guarantee the reliability of measurement results from quantitative analysis performed via microscope with eyes. A calibration curve was created for prove the reliability. A total of three calibration curves were drawn, and as a result of analysis of the calibration curves, all R² values were more than 0.9. This ensures high reliability for quantitative analysis. The qualitative analysis could determine the series of microplastics flowing into the MWTP, but could not confirm the chemical composition of each microplastic. This study can be used to confirm the chemical composition of microplastics introduced into MWTP in the future research.

• Composites Research
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• v.36 no.1
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• pp.1-15
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• 2023

Demand for energy consumption reduction is increasing according to the development expectations of future mobility. Lightweight structural materials are known as a method to reduce greenhouse gas emissions and improve energy efficiency. In particular, fiber reinforced polymer composite (FRP) is attracting attention as a material that can replace existing metal alloys due to its excellent mechanical properties and light weight. In this paper, industrial applications and research trends of carbon fiber reinforced composites (CFRP, carbon FRP) and self-reinforced composites (SRC) were reviewed based on the reinforcement, polymer matrix, and manufacturing process. In order to overcome the expensive process cost and long manufacturing time of the epoxy resin-based autoclave method, which is mainly used in the aircraft field, mass production of CFRP-applied electric vehicles has been reported using a high-pressure resin transfer molding process including fast-curing epoxy. In addition, thermoplastic resin-based CFRP and interface enhancement methods to solve the recycling issue of carbon fiber composites were reviewed in terms of materials and processes. To form a perfect matrix-reinforcement interface, which is known as the major factor inducing the excellent mechanical properties of FRP, studies on SRC impregnated with the same matrix in polymer fibers have been reported. The physical and mechanical properties of SRC based on various thermoplastic polymers were reviewed in terms of polymer orientation and composite structure. In addition, a copolymer matrix strategy for extending the processing window of highly drawn polypropylene fiber-based SRC was discussed. The application of CFRP and SRC as lightweight structural materials can provide potential options for improving the energy efficiency of future mobility.

• Korean Journal of Heritage: History & Science
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• v.55 no.4
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• pp.166-177
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• 2022

The Shiveet Khairkhan is located on Tsengel Som in the middle of Bayan-ulgi Aimag in the Altai region. Various remains have been identified, and it has been found to be an important area of the Eurasian steppe. In this study, the characteristics of textile fibers and dyes excavated from the tombs of the 1st~3rd century Xianbei period in the sites of Shiveet Khairkhan, Mongolia were investigated. As a result of analysis using optical microscopic observation and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) for fiber identification, green and yellow fabrics were identified as silk fabrics. To investigate the properties of the dye, the surface reflectance of the dyed fabric was measured using an fiber optic reflectance spectrophotometer for non-destructive analysis. The green fabric appeared similar to the reflection spectrum of indigo dye. In addition, as a result of component analysis using gas chromatography-mass spectrometry, isatin and indigotine were detected. Isatin and indigotine are characteristic components of indigo dye, and it was found that the green fabric of the tombs of the Xianbei period was dyed using indigo dye. It was difficult to identify the type of dye in the yellow fabric as a result of reflectance spectrum and gas chromatography analysis. Indigo plants are a dye used for blue dyeing from thousands of years ago, and many species are distributed around the world. It was confirmed that the fabric was relatively well preserved and indigo dye was used for the green Jikryeongui (garment with a straight collar) in the ancient tomb of the Xianbei period about 1,800 years ago, even though it was buried for a long time. Scientific investigation of textile cultural heritage is an essential process for conservation treatment, restoration, exhibition, and the creation of a conservation environment. It is expected that related research will be activated in the future and will be helpful in interpreting the living culture at the time, preserving textiles, and a conservation environment.

• Korean Journal of Heritage: History & Science
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• v.56 no.1
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• pp.80-97
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• 2023

By taking wallpaper specimens from Gyeongbokgung Palace, Changdeokgung Palace, and Chilgung Palace preserved from the late Joseon Dynasty to the present, we planned in this study to determine the types and characteristics of the paper used as wallpaper in the Joseon royal family. First, we confirmed the features of paper hanging in the palaces with old literature on the wallpaper used by the royal family based on archival research. Second, we conducted a field survey targeting the royal palaces whose construction period was relatively clear, and analyzed the first layer of wallpaper directly attached to the wall structure after sampling the specimens. Therefore, we confirmed that the main raw material was hanji, which was used as a wallpaper by the royal family, and grasped the types of substances(dyes and pigments) used to produce a blue color in spaces that must have formality by analyzing the blue-colored paper. Based on the results confirmed through the analysis, we checked documents and the existing wallpaper by comparing the old literature related to wallpaper records of the Joseon Dynasty palaces. We also built a database for the restoration of cultural properties when conserving the wallpaper in the royal palaces. We examined the changes in wallpaper types by century and the content according to the place of use by extracting wallpaper-related contents recorded in 36 cases of Uigwe from the 17th to 20th centuries. As a result, it was found that the names used for document paper and wallpaper were not different, thus document paper and wallpaper were used without distinction during the Joseon Dynasty. And though there are differences in the types of wallpaper depending on the period, it was confirmed that the foundation of wallpaper continued until the late Joseon Dynasty, with Baekji(white hanji), Hubaekji(thick white paper), jeojuji(common hanji used to write documents), chojuji(hanji used as a draft for writing documents) and Gakjang(a wide and thick hanji used as a pad). As a result of fiber identification by the morphological characteristics of fibers and the normal color reaction(KS M ISO 9184-4: Graph "C" staining test) for the first layer of paper directly attached to the palace wall, the main materials of hanji used by the royal family were confirmed and the raw materials used to make hanii in buildings of palaces based on the construction period were determined. Also, as a result of analyzing the coloring materials of the blue decorative paper with an optical microscope, ultraviolet-visible spectroscopic analysis(UV-Vis), and X-ray diffraction analysis(XRD), we determined that the type of blue decorative paper dyes and pigments used in the palaces must have formality and identified that the raw materials used to produce the blue color were natural indigo, lazurite and cobalt blue.