• Journal of the Korean Wood Science and Technology
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• 제43권3호
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• pp.364-373
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• 2015

본 연구는 밀도와 귤박첨가율이 다른 톱밥-귤박 파티클보드의 동적 정적탄성계수와 휨강도를 측정, 비교하여 밀도와 귤박의 첨가율이 파티클보드의 역학적 성능에 주는 영향과 동적탄성계수와 정적 휨강도 성능사이의 관계를 조사하였다. 톱밥-귤박 파티클보드의 밀도가 0.4에서 $0.6g/cm^3$로 증가할수록 휨성능은 증가하여, 밀도가 휨성능에 크게 영향하였으며, 밀도 $0.4g/cm^3$와 $0.5g/cm^3$의 톱밥-귤박 파티클보드에서 귤박의 첨가량이 증가할수록 휨성능은 감소하는 경향을 나타내었다. 톱밥-귤박 파티클보드의 동적탄성계수, 정적탄성계수 그리고 휨강도 사이에 높은 상관관계가 확인되었으며 양단 자유 휨진동시험에 의한 동적탄성계수로부터 비파괴적으로 정적 휨강도 성능의 예측이 가능할 것으로 사료되었다.

• Composites Research
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• 제12권3호
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• pp.26-35
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• 1999

복합재료내의 결함을 원공노치로 가정하고 노치의 크기에 따른 정하중 및 피로실험을 수행하였다. 원공이 존재하는 복합재료에 대하여 다양한 수리기법을 적용하여 정하중 실험을 수행하였다. 수리기법중에 precured double patched 방식과 cure-in-place 방식의 수리는 가장 우수한 결과를 보여 평활재의 약 60∼80%의 강도복구효과를 보였다. 우수한 결과기법을 나타낸 수리기법중에 보다 실제적인 방식이라고 사료되는 cure-in-place 방식으로 수리된 재료에 대하여 피로실험을 수행하였다. 수리된 재료는 정하중 및 피로의 경우에 있어서 향상된 결과를 보였으며 피로시 평활재의 거동을 나타낸다. 참고계수를 도입하여 회귀분석된 피로수명예측식(MFLPE's)은 수리된 시편에 비해 타 예측식에 비해 더 좋은 결과를 나타낸다.

• Food Science and Biotechnology
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• 제15권2호
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• pp.264-269
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• 2006

Basic rheological data of dandelion leaf concentrates were determined to predict processing aptitude and usefulness of dandelion leaf concentrates as functional food materials. Hot water and 70% ethanol extracts of dandelion leaves were concentrated at 5, 20, and 50 Brix, and their static and dynamic viscosities, and Arrhenius plots were investigated. Most concentrated dandelion leaves extracted with hot water and 70% ethanol showed flow behaviors close to Newtonian fluid based on power law model evaluation. Apparent viscosity of concentrated dandelion leaves extracted with hot water and 70% ethanol decreased with increasing temperature. Yield stresses of concentrated dandelion leaves extracted with hot water and 70% ethanol by Herschel-Bulkley model application were 0.020-0.641 and 0.017-0.079 Pa, respectively. Activation energies of concentrated dandelion leaves extracted with hot water and 70% ethanol were $2.102-32.669{\times}10^3$ and $1.657-5.382{\times}10^3\;J/mol{\cdot}kg$ with increasing concentration, respectively. Loss modulus (G") predominated over storage modulus (G') at all applied frequencies, showing typical flow behavior of low molecular solution. G' and G" of concentrated dandelion leaves extracted with hot water slowly increased with increasing frequency compared to those of concentrated dandelion leaves extracted with 70% ethanol.

• Advances in nano research
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• 제16권5호
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• pp.445-458
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• 2024

The objective of this paper is to present free vibration and static stability analyses of rotating composite beams reinforced with carbon nanotubes (CNTs) under uniform thermal loads. Beam structural equations and CNT-reinforced composite (CNTRC) beam formulations are derived based on Timoshenko beam theory (TBT). The temperature-dependent properties of the beam material, such as the elastic modulus, shear modulus, and material density, are assumed to vary over the thickness according to the rule of mixture. The beam material is modeled as a mixture of single-walled carbon nanotubes (SWCNTs) in an isotropic matrix. The SWCNTs are aligned and distributed in the isotropic matrix with different patterns of reinforcement, namely the UD (uniform), FG-O, FG-V, FG- Λ and FG-X distributions, where FG-V and FG- Λ are asymmetric patterns. Numerical examples are presented to illustrate the effects of several essential parameters, including the rotational speed, hub radius, effective material properties, slenderness ratio, boundary conditions, thermal force, and moments due to temperature variation. To the best of the authors' knowledge, this study represents the first attempt at the finite element modeling of rotating CNTRC Timoshenko beams under a thermal environment. The results are presented in tables and figures for both symmetric and asymmetric distribution patterns, and can be used as benchmarks for further validation.

• Wind and Structures
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• 제23권6호
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• pp.543-558
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• 2016

The response of functionally graded ceramic-metal plates is investigated using theoretical formulation, Navier's solutions, and a new displacement based on the high-order shear deformation theory are presented for static analysis of functionally graded plates. The theory accounts for a quadratic variation of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. The plates are assumed to have isotropic, two-constituent material distribution through the thickness, and the modulus of elasticity of the plate is assumed to vary according to a power-law distribution in terms of the volume fractions of the constituents. Numerical results of the new refined plate theory are presented to show the effect of the material distribution on the deflections, stresses and fundamental frequencies. It can be concluded that the proposed theory is accurate and simple in solving the static and free vibration behavior of functionally graded plates.

• 한국정밀공학회지
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• 제18권11호
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• pp.34-41
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• 2001

This study is to investigate the energy absorption characteristics of CFRP(Carbon-Fiber Reinforced Plastics) tubes on static and dynamic tests. Axial static compression tests have been carried out using the static testing machine(Shin-gang buckling testing machine) and dynamic compression tests have been utilized using an vertical crushing testing machine. When such tubes are subjected to crushing loads, the response is complex and depends on the interaction between the different mechanisms that could control the crushing process. The collapse characteristics and energy absorption have been examined for various tubes. Energy absorption of the tubes are increased as changes in the lay-up which may increase the modulus of tubes. The results have been varied significantly as a function of ply orientation and interlaminar number.

• Earthquakes and Structures
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• 제23권4호
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• pp.353-361
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• 2022

The dynamic behavior of a single pile was investigated by using analytical and numerical studies. The focus of this study was to develop the dynamic p-y curve of a pile for pseudo-static analysis considering the shear wave velocity of the soil by using three-dimensional numerical analyses. Numerical analyses were conducted for a single pile in dry sand under changing conditions such as the shear wave velocity of the soil and the acceleration amplitudes. The proposed dynamic p-y curve is a shape of hyperbolic function that was developed to take into account the influence of the shear wave velocity of soil. The applicability of pseudo-static analysis using the proposed dynamic p-y curve shows good agreement with the general trends observed by dynamic analysis. Therefore, the proposed dynamic p-y curve represents practical improvements for the seismic design of piles.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.537-543
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• 2003

This paper presents the improved procedure to assess static and dynamic strength of crawler type excavators. A fully integrated model including front attachment and chassis was prepared for structural analysis. In this paper, two types of loading input methods were investigated and the method imposing digging force directly on bucket tooth was more convenient than imposing cylinder reaction force on cylinder pin even if the two methods showed no discrepancy in analysis results. Static strength analysis was carried out for eight analysis scenarios based on two extreme digging positions, maximum digging reach position and maximum digging force positions. The results from static strength analysis were compared with measured stresses, cylinder pressures and digging forces and showed a good quantitative agreement with measured data. Dynamic strength analysis was carried out for simple reciprocation of boom cylinders. It was recognized that the effect of compressive stiffness of hydraulic oil was very important for dynamic structural behavior. The results from dynamic strength analysis including hydraulic oil stiffness were also compared with measured acceleration data and showed a qualitative agreement with measured data.

• Journal of the Korean Wood Science and Technology
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• 제33권5호통권133호
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• pp.13-20
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• 2005

This paper deals with flexural vibration techniques as a means of predicting bending strength properties for quarter-sawn and flat-sawn planes of red pine containing knots. Dynamic modulus of elasticity $(MOE_d)$ was calculated from resonance frequency obtained from the flexural vibration induced by a magnetic driver in quarter-sawn and flat-sawn planes of red pine containing knots. The dynamic MOE were well correlated to bending strength properties. Their correlation coefficients ranged from 0.866 to 0.800 for the regression between dynamic MOE and static bending MOE or MOR. The difference of the values between quarter-sawn and flat-sawn was very small. These values were higher than correlation between percentage of total knot diameter to total width of red pine specimen $(K_T(%))$ as well as $K_O(%)$ base upon ASTM D 3737 and static bending strength properties (correlation coefficient r = 0.448~0.704), and were similar to those between static bending MOE and bending MOR (r = 0.850). These results indicate that dynamic MOE obtained from resonance frequency induced by flexural vibration of magnetic driver is able to effectively use for predicting of static bending strength of red pine containing knots as well as static MOE.

• 대한토목학회논문집
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• 제13권4호
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• pp.239-250
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• 1993

동적 반복 재하식 $M_R$ 시험법은 차량 하중의 반복재하 조건을 실질적으로 반영할 수 있는 이상적인 시험법이기는 하나, 근본적으로 비싼 시험장치가 필요하고, 시험기의 조작에 고도의 전문성이 요구되어 일상적인 시험법으로 채택하기에는 많은 문제점을 안고 있다. 이러한 문제점은 $M_R$ 적용 포장 설계법의 현실적인 적용을 가로막는 주요한 장애요인이 되고 있어 최근에는 보다 간편한 시험장치와 단순한 시험절차를 통하여 동적 반복재하식 시험법에 의한 $M_R$ 값을 효과적으로 얻을 수 있는 대체 $M_R$ 시험법의 개발에 대한 연구의 필요성이 높아지고 있다. 본 연구에서는 노상토의 회복탄성계수를 결정하는데 있어 기존의 동적 반복 재하식의 $M_R$ 시험법을 대신할 수 있는 대체 $M_R$ 시험법의 하나로서, 표준삼축 압축기를 활용할 수 있고 시험법이 간편한 정적 반복 재하식 $M_R$ 시험법을 개발하였다. 그리고 국내에서 노상토 재료로 널리 쓰이는 대표적인 흙에 대한 일련의 실험을 통하여 개발된 정적 반복 재하식 $M_R$ 시험법의 타당성 및 적용한계를 분석하였다.