• Journal of the Speleological Society of Korea
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• v.56
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• pp.15-38
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• 1998

Biomass and soil properties of plant communites was investigated in the limestone ares, Tanyang, Ch'ungbuk Province in Korea. Plants was classified in calcicoles and calcifuges within plant communities occurring in the limestone area. Biomass of plant populatins in the limestone area was measured that Stellaria aquatica was the lowest(0.58g/plant), Chrysanthemum boreale was the highest(8.87g/plant) and that Pennisetum alopecuroides, Miscanthus sinensis was 6.67g/plant, 5.76g/plant, respectively. Diameter of breast height among the tree layer communities was investigated that Pinus densiflora was the widest(20cm), Juniperus rigida was the narrowest(6cm) and that Quercus aliena, Populus ${\times}$ tomentiglandulosa was 10cm, 12cm, respectively. The high of density in the tree layer was found out Populus ${\times}$ tomentiglandulosa, Juniperus rigida, Quercus aliena, Pinus densiflora in this order. Dominant species in the study area were Pinus densiflora, Quercus aliena, Juniperus rigida, Quercus dentata in the tree layer, Lespedeza bicolor, Buxus microphylla, Rhus chinensis in the shrub layer, Humulus Japonicus, Erigeron canadensis, Xanthium strumarium, Oenothera odorata Persicaria hypropiper on the riverside, Pennisetum alopecuroides, Vicia amoena, Chrysanthemum boreale on the roadside. Soil properties of the limestone area was investigated around the protrusion of rock in the upper region, around the cave and underlayer accumulated by corrosion in the study area. Lime-chlorosis was observed in the upper region, underlayer and around the cave. It was observed that biota of kum-gul and dungbong-gul was Rhinolophus ferrumequinum korai, Epanerchodus kimi, Antrokoreana gracilipes, Diestrammena japonical. Dominant species were Humulus japonicus, Stellaria aquatica, Hydrocotyle maritima, Phragmites communis, Miscanthus sinensis around the inlet of a kum-gul. It was classified that plants in the study area was 34 order, 53 family, 135 species in all. Calcicoles were 11 order, 16 family, 18 species and calcufuges were 6 order, 8 family, 11 species of them all.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1027-1035
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• 2016

In this study, a strain-controlled fatigue test of widely-used 316L stainless steel with excellent corrosion resistance and mechanical properties was conducted, in order to assess its fatigue life. Low cycle fatigue behaviors were analyzed at room temperature, as a function of the strain amplitude and strain ratio. The material was hardened during the initial few cycles, and then was softened during the long post period, until failure occurred. The fatigue life decreased with increasing strain amplitude. Masing behavior in the hysteresis loop was shown under the low strain amplitude, whereas the high strain amplitude caused non-Masing behavior and reduced the mean stress. Low cycle fatigue life prediction based on the cyclic plastic energy dissipation theory, considering Masing and non-Masing effects, showed a good correlation with the experimental results.

• Journal of Welding and Joining
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• v.26 no.5
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• pp.49-59
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• 2008

Hastelloy C-276, corrosion resistant alloy at high temperature, is used in chemical plant and power generation industry. In this study, process parameter of laser welding for welding property in Hastelloy C-276 using a continuous wave Nd:YAG laser was studied. As the result of experiment, laser welding did not show segregation or crack at heat affected zone compared to conventional GTWA welding. The melting zone showed cell dendritic structure along with welding line. In addition, planer front solidification is occurred from welding structure, and it was progressed to cellular solidification. Optimal process parameter for butt welding was 1.2kW and 2.0 m/min for laser power and welding speed, respectively. While heat input, output density, tensile stress, and longitudinal strain was $441.98{\times}103$ J/cm2, $29.553{\times}103$ W/cm2, 768 MPa, and 0.689, respectively. Lap welding of the same material showed greater discrepancy in tensile property during 1 line and 2 line welding. For 1 line welding, tensile stress was about 320 MPa, and 2 line showed slightly larger tensile stress. However, strain was decreased by 20%. From this result, lap welding of the same material, Hastelloy C-276, with 2 line welding is considered to be more effective process than 1 line welding with consideration of mechanical property.

• Korean Journal of Materials Research
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• v.20 no.3
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• pp.125-131
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• 2010

In this study, Ti powders were fabricated from Ti scrap by the Hydrogenation-Dehydrogenation (HDH) method. The Ti powders were prepared from the spark plasma sintering (SPS) and their microstructure was investigated. Hydrogenation reactions of Ti scrap occurred at near $450^{\circ}C$ with a sudden increase in the reaction temperature and the decreasing pressure of hydrogen gas during the hydrogenation process in the furnace. The dehydrogenation process was also carried out at $750^{\circ}C$ for 2 hrs in a vacuum of $10^{-4}$ torr. After the HDH process, deoxidation treatment was carried out with the Ca (purity: 99.5%) at $700^{\circ}C$ for 2 hrs in the vacuum system. It was found that the oxidation content of Ti powder that was deoxidized with Ca showed noticeably lower values, compared to the content obtained by the HDH process. In order to fabricate the Ti compacts, Ti powder was sintered under an applied uniaxial punch pressure of 40 MPa in the range of $900-1200^{\circ}C$ for 5 min under a vacuum of $10^{-4}$ torr. The relative density of the compact was 99.5% at $1100^{\circ}C$ and the tensile strength decreased with increasing sintering temperature. After sintering, all of the Ti compacts showed brittle fracture behavior, which occurred in an elastic range with short plastic yielding up to a peak stress. Ti improved the corrosion resistance of the Ti compacts, and the Pd powders were mixed with the HDH Ti powders.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.2
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• pp.216-222
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• 2021

This is an experiment to complement new ways of using concentrated water discharged from the seawater desalination plant. In this study, metakaolin, which has excellent chloride ion immobilization effect, was used as the main binder, and 10% and 20% of calcium oxide were substituted with the activator. In addition, tap-water(TW) and reverse osmosis brine water(RW) were used as mixed water. As a result of the experiment, the mixture using RW showed higher compressive strength than TW. It also showed low water absorption and high density. In the mixture using RW as mixed water, a hydration reaction substance called Friedel's salt could be observed. Considering the corrosion problem of steel, RW is considered to be applicable to products such as non-reinforced concrete, brick, and curb stone. Through this study, it is thought that it is meaningful to propose a new application method other than the ocean release of RW.

• Korean Chemical Engineering Research
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• v.57 no.2
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• pp.172-176
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• 2019

A benthic microbial fuel cells(BMFC) is fuel cell using electricity produced by decomposing organic matter in a sea or a lake. In this study, we used a gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEMFC) as a BMFC electrode to find out the operation conditions with high performance. The performance of BMFC was increased as resistance of external resistor increased. It was possible to maintain the performance by avoiding the increase of the contact resistance with the electrode due to corrosion of the lead wire in seawater. The bubble generator was able to increase the maximum power density by more than 2 times and the optimum operating temperature was $40^{\circ}C$.

• Korean Journal of Materials Research
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• v.28 no.11
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• pp.653-658
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• 2018

$ZrO_2$ is a candidate material for hip and knee joint replacements because of its excellent combination of biocompatibility, corrosion resistance and low density. However, the drawback of pure $ZrO_2$ is a low fracture toughness at room temperature. One of the most obvious tactics to cope with this problem is to fabricate a nanostructured composite material. Nanomaterials can be produced with improved mechanical properties(hardness and fracture toughness). The high-frequency induction heated sintering method takes advantage of simultaneously applying induced current and mechanical pressure during sintering. As a result, nanostructured materials can be achieved within very short time. In this study, W and $ZrO_2$ nanopowders are mechanochemically synthesized from $WO_3$ and Zr powders according to the reaction($WO_3+3/2Zr{\rightarrow}W+3/2ZrO_2$). The milled powders are then sintered using high-frequency induction heating within two minutes under the uniaxial pressure of 80MPa. The average fracture toughness and hardness of the nanostructured W-3/2 $ZrO_2$ composite sintered at $1300^{\circ}C$ are $540kg/mm^2$ and $5MPa{\cdot}m^{1/2}$, respectively. The fracture toughness of the composite is higher than that of monolithic $ZrO_2$. The phase and microstructure of the composite is also investigated by XRD and FE-SEM.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.1
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• pp.24-30
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• 2019

The deck floor of a the cargo truck becomesis damaged and aged due to the continuous loading of the loading cargo and external environmental factors. Floor boards made of wood and metal are often used. In the case of wood, the cost is high due to the use of imported wood, and the strength is easily deterioratesd due to environmental factors. In the case of metal materials, the durability is higher than that of wood, but problems are raised due to the effect of major factors that hinder the weight reduction, and the effects of corrosion. In order to replace this stucturestructural design, this study proposed a wood fiber composite using natural raw materials. Woody composites are being used as environmentally and friendly exterior materials with the combined advantages of plastic, and wood,; low cost and low density. However, due to the nature of the woody composites, the properties are differentdiffer depending on the contents of the matrix, reinforcing agent, additives, compatibilizer, etc. In this study, we investigate these problems through analysis of the microstructure and mechanical properties according to proper content and injection molding conditions. As a result, it is considered that the wood deck composite can replaced the current Deck Floor Boardreplace current deck floor boards through continuous continued research and results of this study.

• Journal of Powder Materials
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• v.28 no.5
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• pp.389-395
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• 2021

Oxide dispersion-strengthened (ODS) steel has excellent high-temperature properties, corrosion resistance, and oxidation resistance, and is expected to be applicable in various fields. Recently, various studies on mechanical alloying (MA) have been conducted for the dispersion of oxide particles in ODS steel with a high number density. In this study, ODS steel is manufactured by introducing a complex milling process in which planetary ball milling, cryogenic ball milling, and drum ball milling are sequentially performed, and the microstructure and high-temperature mechanical properties of the ODS steel are investigated. The microstructure observation revealed that the structure is stretched in the extrusion direction, even after the heat treatment. In addition, transmission electron microscopy (TEM) analysis confirmed the presence of oxide particles in the range of 5 to 10 nm. As a result of the room-temperature and high-temperature compression tests, the yield strengths were measured as 1430, 1388, 418, and 163 MPa at 25, 500, 700, and 900℃, respectively. Based on these results, the correlation between the microstructure and mechanical properties of ODS steel manufactured using the composite milling process is also discussed.

• Korean Journal of Materials Research
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• v.32 no.1
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• pp.44-50
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• 2022

Transition metal carbides (TMCs) are used to process difficult-to-cut materials due to the trend of requiring superior wear and corrosion properties compared to those of cemented carbides used in the cutting industry. In this study, TMC (TiC, TaC, Mo₂C, and NbC)-based cermets were consolidated by spark plasma sintering at 1,300 ℃ (60 ℃min) with a pressure of 60 MPa with Co addition. The sintering behavior of TMCs depended exponentially on the function of the sintering exponent. The Mo₂C-6Co cermet was fully densified, with a relative density of 100.0 %. The Co-binder penetrated the hard phase (carbides) by dissolving and re-precipitating, which completely densified the material. The mechanical properties of the TMCs were determined according to their grain size and elastic modulus: TiC-6Co showed the highest hardness of 1,872.9 MPa, while NbC-6Co showed the highest fracture toughness of 10.6 MPa^*m^1/2. The strengthened grain boundaries due to high interfacial energy could cause a high elastic modules; therefore, TiC-6Co showed a value of 452 ± 12 GPa.