• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.4
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• pp.721-726
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• 2017

We fabricated stretchable thin-film transistors(TFTs) on a polydimethylsiloxane substrate with patterned polyimide island structures by using an amorphous InGaZnO semiconductor and parylene gate insulator. The TFTs exhibited a field- effect mobility of $5cm^2V^{-1}s^{-1}$ and a current on/off ratio of $10^5$ at a relatively low operating voltage. Furthermore, the fabricated transistors showed no noticeable changes in their electrical performance for large strains of up to 50 %.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1569-1580
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• 2001

A new nonlinear near-wall turbulence model is developed to predict turbulent flow and heat transfer in strongly nonequilibrium flows. The k-$\varepsilon$-f$\sub$${\mu}$/, model of Park and Sung$\^$(1)/ is extended to a nonlinear formulation. The stress-strain relationship is the thrid-order in the mean velocity gradients. The strain dependent coefficients are obatined from the realizability constraints and the singular behavior at large strains. An improved explicit heat flux model is proposed with the aid of Cayley-Hamilton theorem. This new model includes the quadratic effects of flow deformations. The near-wall asymptotic behavior is incorporated by modifying the f$\sub$λ/ function. The model performance is shown to be satisfactory.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.219-223
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• 2009

This paper prescribed the structural integrity of the API 5L X65 pipeline subjected to tensile pre-strain. The effects of pre-strain on the mechanical properties of API 5L X65 pipe were substantially investigated through a variety of the experimental procedures. Axial tensile pre-strain of 1.5, 5 and 10% was applied to plate-type tensile specimens cut from the pipe body prior to mechanical testing. Tensile test revealed that yield strength and tensile strength were increased with increasing tensile pre-strain. The increasing rate of the yield strength owing to the pre-strain is greater than that of the tensile strength. However, the pre-strain up to 5% had a little effect on the decreasing of the fracture toughness. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for service code.

• Computers and Concrete
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• v.1 no.2
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• pp.151-168
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• 2004

A two-dimensional nonlinear finite element model is developed to simulate time-dependent cracking of reinforced concrete members under service loads. To predict localized cracking, the crack band model is employed to model individual crack opening. In conjunction with the crack band model, a bond-interface element is used to model the slip between concrete and reinforcing steel permitting large slip displacements between the concrete element nodes and the steel truss element nodes at crack openings. The time-dependent effects of concrete creep and shrinkage are incorporated into the smeared crack model as inelastic pre-strains in an iterative solution procedure. Two test examples are shown to verify the finite element model with good agreement between the model and the observed test results.

• Computers and Concrete
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• v.16 no.5
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• pp.683-701
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• 2015

When approached using nonlinear finite element (FE) techniques, structural analyses generate, for real RC structures, large complex numerical problems. Damage is a major part of concrete behavior, and the discretization technique is critical to limiting the size of the problem. Based on previous work, the ${\mu}$ damage model has been designed to activate the various damage effects correlated with monotonic and cyclic loading, including unilateral effects. Assumptions are formulated to simplify constitutive relationships while still allowing for a correct description of the main nonlinear effects. After presenting classical 2D finite element applications on structural elements, an enhanced simplified FE description including a damage description and based on the use of multi-fiber beam elements is provided. Improvements to this description are introduced both to prevent dependency on mesh size as damage evolves and to take into account specific phenomena (permanent strains and damping, steel-concrete debonding). Applications on RC structures subjected to cyclic loads are discussed, and results lead to justifying the various concepts and assumptions explained.

• 한국균학회소식:학술대회논문집
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• 2018.05a
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• pp.49-49
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• 2018

A variety of bioactive secondary metabolites have been reported from plant-associated microorganisms. Halophytes, plants that can only grow in hypersaline area, were reported to host beneficial microorganisms such as plant growth-promoting endophytes. The microorganisms have been reported to show notable mutualistic symbiosis with halophytes to help them survive in high saline condition. Finding out bioactive secondary metabolites as well as elucidation of relationship(s) between microbes and the host halophyte has been paid attention, because of their functional diversity. Novel microbes often have associated with novel natural products. In an effort to investigate natural compounds with interesting structures from fungi, we selected plants from a distinct environmental setting which could be a promising source. Several fungi were isolated from halophyte or medicinal plants. Some strains of the fungi were cultivated on a large scale and extracted with ethyl acetate, which were subjected to a series of chromatographic methods, leading to the isolation of tens of compounds. The isolated compounds were identified by analysis of spectroscopic methods such as 1D-, 2D-NMR, and MS. Details of isolation, structure determination, and biological activities will be discussed.

• Mycobiology
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• v.46 no.3
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• pp.205-214
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• 2018

The order Mucorales, the largest in number of species within the Mucoromycotina, comprises typically fast-growing saprotrophic fungi. During a study of the fungal diversity of undiscovered taxa in Korea, two novel mucoralean strains, CNUFC-GWD3-9 and CNUFC-EGF1-4, were isolated from specific habitats including freshwater and fecal samples, respectively. On the basis of their morphological characteristics and sequence analyses of internal transcribed spacer and large subunit ribosomal DNA, the CNUFC-GWD3-9 and CNUFC-EGF1-4 isolates were confirmed to be Gilbertella persicaria and Pilobolus crystallinus, respectively. It is ecologically, pathologically, and mycologically significant to find such rare zygomycetous fungi in such specific habitats.

• Transactions of Materials Processing
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• v.13 no.8
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• pp.671-677
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• 2004

For the large reduction in tube cross section, the tube drawing process is usually performed by two successive passes, so called first drawing and second drawing. In multi-pass drawing process, the reduction balance is important to prevent drawing cracks. Therefore in this study, the model for uniform reduction distribution in two-pass drawing process has been developed on the basis of cross sectional variation of drawn tube. For the given product geometry the model provides optimal diameter and thickness that can evenly distribute drawing reductions. The capability of model is well confirmed by finite element analysis of tube drawing process. Criteria curves at various limit strains to determine whether the drawn tube would fail during drawing process are also proposed by using newly developed model.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.4
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• pp.85-91
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• 2004

The objective of the present paper is to develop an analysis method for the correction of welding deformation of stiffened plate by line heating. In this paper, the equivalent loading method, based on the inherent strain theory, was used to analyze the heat-straightening of a stiffened plate. Equivalent loads were obtained by integrating the inherent strains which were determined from the highest temperature and the degree of restraint. Finally, the obtained equivalent loads were imposed, as applied loads, on the elastic analysis for the prediction of correction of welding deformation in stiffened plate. The proposed method is expected as a basic study in heat-straightening analysis of welding deformation in large scale block.

• Steel and Composite Structures
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• v.17 no.6
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• pp.951-965
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• 2014

Point bending is commonly used for cambering and curving steel girders to large radii. In this system, a hydraulic ram or press is used to apply concentrated loads at selected points to obtain the required vertical (cambering) or horizontal (curving) curved profile from induced permanent deformations. This paper derives closed form solutions that relate loads to permanent deformations for horizontally curving wide flange steel beams based on their post-yield response. These solutions are presented in a parametric form to identify the relationship between key variables and their impact on the accuracy of the curving operation. It is shown that point bending could yield parabolic curved profiles that are within 1% of a desired circular curve if the span length to radius of curvature ratio (L / R) is less than 1.5 and the point loads are spaced at one third the beam length. Safe limits are then established on loads, strains and curvatures to avoid damaging the steel section. This leads to optimization of the point bending operation for inducing a circular profile in wide flange steel beams of any size.