• Title/Summary/Keyword: high strength materials

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Development of GDL-carbon Composite Bipolar Plate Assemblies for PEMFC (PEM 연료전지용 가스확산층-탄소 복합재료 분리판 조합체 개발)

  • Lim, Jun Woo
    • Composites Research
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    • v.34 no.6
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    • pp.406-411
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    • 2021
  • PEM (proton exchange membrane) fuel cells generate only water as a by-product, and thus are in the spotlight as an eco-friendly energy source. Among the various components composing the stack of the fuel cell, research on the bipolar plate that determines the efficiency of the fuel cell is being actively conducted. The composite bipolar plate has high strength, rigidity and corrosion resistance, but has the disadvantage of having a relatively low electrical conductivity. In this study, to overcome these shortcomings, a gas diffusion layer (GDL)-composite bipolar plate assembly was developed and its performance was experimentally verified. The graphite foil coating method developed in the previous study was applied to reduce the contact resistance between the bipolar plate and the GDL. In addition, in order to improve electron path in the stack and minimize the contact resistance between the GDL and the bipolar plate, a GDL-bipolar plate assembly was fabricated using a thin metal foil. As a result of the experiment, it was confirmed that the developed GDL-bipolar plate assembly had 98% lower electrical resistance compared to the conventional composite bipolar plate.

Recent advances in seaweed seedling production: a review of eucheumatoids and other valuable seaweeds

  • Jiksing, Calvin;Ongkudon, McMarshall M.;Thien, Vun Yee;Rodrigues, Kenneth Francis;Yong, Wilson Thau Lym
    • ALGAE
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    • v.37 no.2
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    • pp.105-121
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    • 2022
  • Modern seaweed farming relies heavily on seedlings from natural beds or vegetative cuttings from previous harvests. However, this farming method has some disadvantages, such as physiological variation in the seed stock and decreased genetic variability, which reduces the growth rate, carrageenan yield, and gel strength of the seaweeds. A new method of seedling production that is sustainable, scalable, and produces a large number of high-quality plantlets is needed to support the seaweed farming industry. Recent use of tissue culture and micropropagation techniques in eucheumatoid seaweed production has yielded promising results in increasing seed supply and growing uniform seedlings in large numbers in a shorter time. Several seaweed species have been successfully cultured and regenerated into new plantlets in laboratories using direct regeneration, callus culture, and protoplast culture. The use of biostimulants and plant growth regulators in culture media increases the seedling quality even further. Seedlings produced by micropropagation grew faster and had better biochemical properties than conventionally cultivated seedlings. Before being transferred to a land-based grow-out system or ocean nets for farming, tissue-cultured seedlings were recommended to undergo an acclimatization process to increase their survival rate. Regular monitoring is needed to prevent disease and pest infestations and grazing by herbivorous fish and turtles during the farming process. The current review discusses recent techniques for producing eucheumatoid and other valuable seaweed farming materials, emphasizing the efficiency of micropropagation and the transition from laboratory culture to cultivation in land-based or open-sea grow-out systems to elucidate optimal conditions for sustainable seaweed production.

Stress and fatigue analysis of major components under dynamic loads for a four-row tractor-mounted radish collector

  • Khine Myat Swe;Md Nasim Reza;Milon Chowdhury;Mohammod Ali;Sumaiya Islam;Sang-Hee Lee;Sun-Ok Chung;Soon Jung Hong
    • Korean Journal of Agricultural Science
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    • v.49 no.2
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    • pp.269-284
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    • 2022
  • The development of radish collectors has the potential to increase radish yields while decreasing the time and dependence on human labor in a variety of field activities. Stress and fatigue analyses are essential to ensure the optimal design and machine life of any agricultural machinery. The objectives of this research were to analyze the stress and fatigue of major components of a tractor-mounted radish collector under dynamic load conditions in an effort to increase the design dependability and dimensions of the materials. An experiment was conducted to measure the shaft torque of stem-cutting and transferring conveyor motors using rotary torque sensors at different tractor ground speeds with and without a load. The Smith-Watson-Topper mean stress equation and the rain-flow counting technique were utilized to determine the required shear stress with the distribution of the fatigue life cycle. The severity of the operation was assessed using Miner's theory. All running conditions produced more than 107 of high cycle fatigue strength. Furthermore, the highest severity levels for motor shafts used for stem cutting and transferring and for transportation joints and cutting blades were 2.20, 4.24, 2.07, and 1.07, and 1.97, 3.81, 1.73, and 1.07, respectively, with and without a load condition, except for 5.24 for a winch motor shaft under a load. The stress and fatigue analysis presented in this study can aid in the selection of the most appropriate design parameters and material sizes for the successful construction of a tractor-mounted radish collector, which is currently under development.

Fabrication of silver stabilizer layer by coating process using nano silver paste on coated conductor (나노실버페이스트를 사용하는 코팅공정에 의한 coated conductor의 은 안정화층 제조)

  • Lee, Jong-Beom;Kim, Byeong-Joo;Kim, Hye-Jin;Yoo, Yong-Su;Lee, Hee-Gyoun;Hong, Gye-Won
    • Progress in Superconductivity and Cryogenics
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    • v.11 no.1
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    • pp.1-4
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    • 2009
  • Mechanical and electrical properties of silver stabilizer layer of coated conductor, which as prepared with nano silver paste as starting materials, have been investigated, Nano silver paste was coated on a YBCO film by dip coating process at a diping speed of 20m/min. Coated film was dried in air and heat treated at $400{\sim}700^{\circ}C$ in an oxygen atmosphere. Adhesion strength between YBCO and silver layer was measured by a tape est(ASTM D 3359). Hardness and electrical conductivity of the samples were measured by pencil hardness test (ASTM D 3363) and volume resistance test by LORESTA-GP (MITSHUBISHD, respectively. The sample heat-treated at $500^{\circ}C$ showed poor adhesion 1B, but samples heat treated at higher than $600^{\circ}C$ showed enhanced adhesion of 5B. The silver layer heat-treated at $700^{\circ}C$ showed the high hardness value larger than 9 H, low volume resistance, surface resistance value as well as superior current carrying capacity compared to sputtered silver. SEM observations showed that a dense silver layer was formed with a thickness of about $2{\mu}m$. Dip coated silver layer prepared by using nano silver paste showed superior electrical and mechanical characteristics.

Engineering Characteristics and Pilot Test of Pohang Area's Tertiary Mudstone as Earth Filling Material (성토매립재로서 포항지역 제3기층 이암의 공학적 특성 및 시험시공)

  • Lee, Kyu-Hwan;Jung, Dae-Suck;Kim, Sung-Wook
    • Journal of the Korean Geotechnical Society
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    • v.26 no.1
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    • pp.63-73
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    • 2010
  • The supply of high quality filling materials for pavement base course or reclamation is getting harder. So, there is an attempt to use soft mudstones as an earth filling material in Pohang area. But the engineering properties of the soil deposit placed with soft mudstones have not been clearly evaluated yet. We investigated the water absorption and softening, the slaking behavior and the geological mechanism in order to obtain an effective way of estimating the magnitude of land subsidence and the reduction of soil strength. The applicability of soft mudstones is examined by a variety of laboratory tests and pilot-scale field tests. In addition, it is necessary to consider the environmental characteristics of soft mudstones as a reclaiming material, Consequently, the results from the current study can be used to prevent any construction defects due to the careless use of soft mudstones for the pavement base course or reclamation.

Effect of Heat Treatment on Mechanical Properties of Cross-Linked Ultra-High Molecular Weight Polyethylene Used for Artificial Joint Liner (인공관절 라이너용 가교된 초고분자량폴리에틸렌(UHMWPE)의 열처리 조건에 따른 기계적 특성 변화)

  • Kim, Hyun-Mook;Kim, Dong-Hoon;Gu, Ja-Uk;Choi, Nak-Sam;Kim, Sung-Kon
    • Composites Research
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    • v.22 no.2
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    • pp.1-6
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    • 2009
  • The mechanical characteristics of gamma-ray irradiated UHMWPE specimens were investigated under various heat treatment conditions. The heat treatment was performed in the range of annealing and remelting temperatures. The annealing treatment below the temperature of $130^{\circ}C$ hardly induced changes in the tensile strength, the strain at the failure and the hardness. However the remelting treatment above $140^{\circ}C$ deteriorated those mechanical properties. It was shown in an FTIR analysis that the annealing treatment caused some oxidation of free radicals created by the pretreatment of the irradiation. These quantitative data represented by the behavior of mechanical properties might be used as basic informations for the design and analysis of various artificial joints.

Measurement of Tensile and Bending Properties of Nanohoneycomb Structures (나노허니컴 구조물의 인장 및 굽힘 물성 측정)

  • Jeon, Ji-Hoon;Choi, Duk-Hyun;Lee, Pyung-Soo;Lee, Kun-Hong;Park, Hyun-Chul;Hwang, Woon-Bong
    • Composites Research
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    • v.19 no.6
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    • pp.23-31
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    • 2006
  • We measured mechanical properties, including Young's modulus, effective bending modulus and nominal fracture strength of nanohoneycomb structures using an Atomic Force Microscope(AFM) and a Nano-Universal Testing Machine(UTM). Anodic aluminum oxide(AAO) films are well suited as nanohoneycomb structures because of the simple fabrication process, high aspect ratio, self-ordered hexagonal pore structure, and simple control of pore dimensions. Bending tests were carried out for cantilever structures by pressing AFM tips, and the results were compared with three-point bending tests and tensile tests using a Nano-UTM. One side of the AAO films is clogged by harrier layers, and looks like a face material of conventional sandwich structures. Analysis of this layer showed that it did not influence the bending rigidity, and was just a crack tip. The present results can act as a design guideline in applications of nanohoneycomb structures.

Assessment for Extending Span Ranges of PSC Girder Bridges : I. Proposed Strategy to Estimate the Spans (PSC 거더교의 장경간화 평가 기법 : I. 경간 평가 기법의 제안)

  • Jeon, Se Jin;Choi, Myoung Sung;Kim, Young Jin
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.3A
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    • pp.235-241
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    • 2009
  • PSC girder bridge is known to be more economical than other types of bridges and has been usually applied to a span range of 25 m to 35 m according to the standard shapes for highway bridges in Korea. The spans of the recently developed new types of PSC girders are also limited to 50 m at most. In this study, therefore, feasibility of the long-span PSC girder that reaches more than 50 m is investigated by applying several strategies from the perspectives of materials, design and construction. A systematic procedure is proposed that can be used to assess the effect of each strategy on the span. The proposed scheme adopts a graphical approach that represents a relationship between the number of prestressing tendons and the span, and is derived on a basis of safety assessment equations of the girder in each stage of fabrication and in service. In the companion paper, the amount of span extension is quantitatively evaluated by applying the proposed scheme into a sample PSC girder bridge.

A Review of the Physical Performance of Lightweight Aerated Concrete for Use as an Interior Core Material in Fire Doors (방화문 내부 심재로 적용하기 위한 경량기포콘크리트의 물리적 성능 검토)

  • Hong, Sang-Hun;Kim, Bong-Joo;Jung, Ui-In;Kim, Hae-Nah;Park, Jun-Seo
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2023.05a
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    • pp.111-112
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    • 2023
  • With the development of cities, the density of the population is continuously increasing as buildings become larger and more high-rise, but since the Haeundae residential complex fire in Busan in 2010, there has been a growing need to meet the fire protection performance of buildings as large-scale fires continue to occur every year. On the other hand, fire doors, which are one of the fire protection performance of buildings, have been judged unqualified in 82% of cases when fire doors constructed on the actual site were inspected after completion. The reason for this is that paper honeycomb and glasswool, which are used as core materials for fire doors, absorb moisture, reducing thermal insulation performance, and sagging due to increased weight, leading to performance degradation due to warping in empty spaces. To overcome these problems, research is underway to apply lightweight aerated concrete, an inorganic material, as a core material. Therefore, in order to select a blowing agent that produces stable bubbles prior to the production of lightweight bubble concrete for application as a fire door inner core, this study examined the physical performance according to the type of blowing agent and dilution concentration, and the following conclusions were drawn. Compared to vegetable bubbles and independent bubbles, synthetic bubbles have 3~8% higher thermal conductivity than independent bubbles, but 3~6% lower slurry density than vegetable bubbles, and 2~13% higher compressive strength, which is thought to be an improvement of synthetic bubbles.

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A Study on Crystalline Structural Variations of the Rigid Spherical-Tip scratch on the Surface of α-Titanium substrates via Molecular Dynamics Simulations (α-티타늄 평판표면에서 강체 구형팁의 스크래치로 인한 내부 결정구조 특성 변화에 대한 연구)

  • Yeri Jung;Jin Ho Kim;Taeil Yi
    • Tribology and Lubricants
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    • v.39 no.5
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    • pp.167-172
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    • 2023
  • Titanium alloys are widely recognized among engineering materials owing to their impressive mechanical properties, including high strength-to-weight ratios, fracture toughness, resistance to fatigue, and corrosion resistance. Consequently, applications involving titanium alloys are more susceptible to damage from unforeseen events, such as scratches. Nevertheless, the impact of microscopic damage remains an area that requires further investigation. This study delves into the microscopic wear behavior of α-titanium crystal structures when subjected to linear scratch-induced damage conditions, utilizing molecular dynamics simulations as the primary methodology. The configuration of crystal lattice structures plays a crucial role in influencing material properties such as slip, which pertains to the movement of dislocations within the crystal structure. The molecular dynamics technique surpasses the constraints of observing microscopic phenomena over brief intervals, such as sub-nano- or pico-second intervals. First, we demonstrate the localized transformation of lattice structures at the end of initialization, indentation, and wear processes. In addition, we obtain the exerted force on a rigid sphere during scratching under linear movement. Furthermore, we investigate the effect of the relaxation period between indentation and scratch deformation. Finally, we conduct a comparison study of nanoindentation between crystal and amorphous Ti substrates. Thus, this study reveals the underlying physics of the microscopic transformation of the α-titanium crystal structure under wear-like accidental events.