• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.181-182
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• 2006

Cylindrical specimens with different levels of density have been submitted to uniaxial compression tests with loading and unloading cycles. The analysis of the elastic loadings shows a non linear elasticity which can be mathematically represented by means of a potential law. Results are explained by assuming that the total elastic strain is the contribution of two terms one deriving from the hertzian deformation of the contacts among particles and another that takes into account the linear elastic deformation of the powder skeleton. A simple model based in an one pore unit cell is presented to support the mathematical model.

• Steel and Composite Structures
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• 제47권4호
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• pp.503-511
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• 2023

Stability of laminated plate under thermal load varied linearly along thickness, is developed using a higher order displacement field which depend on a parameter "m", whose value is optimized to get results closest to three-dimension elasticity results. Hamilton, s principle is used to derive equations of motion for laminated plates. These equations are solved using Navier-type for simply supported boundary conditions to obtain non uniform critical thermal buckling and fundamental frequency under a ratio of this load. Many design parameters of cross ply and angle ply laminates such as, number of layers, aspect ratios and E1/E2 ratios for thick and thin plates are investigated. It is observed that linear and uniform distribution of temperature reduces plate frequency.

• 자원ㆍ환경경제연구
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• 제23권3호
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• pp.473-496
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• 2014

본 논문은 이산화탄소 배출량과 소득과의 비선형적인 관계를 시간변동계수를 갖는 공적분모형으로 추정하였다. 특히 이산탄소배출량의 소득효과를 시간에 따라 서서히 변하는 것으로 모형화하였고, 이를 비모수적 방법을 이용하여 추정하였다. 추정결과 선진국의 경우 소득탄력성이 시간에 대해 감소하는 것으로 추정된 반면에 개발도상국의 소득탄력성은 시간에 따라 점차 증가하는 것으로 추정되었다. 이 같은 결과는 경제 발전단계에 따라 소득이 이산화탄소 배출량에 미치는 영향이 다르다는 환경쿠즈네츠곡선에서 의미하는 것과 일치하는 결과이고, 또한 기후변화협약과 교토의정서 상에서 의무준수 대상국(Annex I)과 Non-Annex I 국가 구분이 필요하다는 것을 반증한다. 이러한 차이는 선진국에 비하여 개도국의 경우 소득에 따른 이산화탄소 배출이 상대적으로 더욱 가속화될 수 있음을 의미하며, 이는 기후변화협약 상에서 개도국에 대한 기술이전 및 재정지원이 지속적으로 필요하다는 것에 대한 근거로 활용될 수 있다.

• 자원ㆍ환경경제연구
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• 제13권4호
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• pp.593-619
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• 2004

본 연구는 우리나라 제조업부문에서 사용하고 있는 연료용 에너지원간의 대체관계를 정태 및 동태 선형 logit 모형을 이용하여 실증분석하여 이산화탄소 배출과 관련된 시사점을 살펴보고자 하였다. 연료용 에너지원을 석유, 전력, 도시가스 및 석탄으로 분류하여 1981년~2002년까지의 연간자료를 이용한 추정결과를 요약하면, 첫째로 석탄의 가격탄력성은 비록 절대치에서는 작지만 지속적으로 증가하는 추세를 보이고 있는 반면에, 도시가스의 가격탄력성이 다른 에너지원들에 비해서 크지만 1997년 이후 감소하는 추세를 보이고 있다. 한편, 석유와 전력의 가격탄력성은 비탄력적으로 안정적인 추세를 나타내고 있다. 각 에너지원의 교차탄력성의 추세에 있어서 가장 두드러진 특징은 도시가스의 가격 상승에 따른 다른 에너지원으로의 대체 현상이 공통적으로 1997년 이후 가장 크게 나타나고 있다는 점이다. 특히, 도시가스의 가격 상승에 따른 석탄 및 석유로의 대체효과가 점증하는 것으로 나타나고 있다. 정책적 시사점으로 첫째, 석유와 석탄의 가격탄력성이 비탄력적인 것은 향후 제조업부문에서 연료용 화석연료에 대한 의존도가 지속될 것이라는 점이다. 둘째로, 도시가스의 가격이 상승하는 경우 석유와 석탄으로의 대체효과가 크다는 것이다. 따라서, 온실가스배출 저감을 위한 에너지 가격 정책으로는 도시가스의 가격 인하가 석탄과 석유의 소비 감소에 가장 효과적인 것으로 보인다. 이에 대한 시사점은 앞으로 지속적인 연구를 통해서 검증해 나가야 할 것이다.

• Structural Engineering and Mechanics
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• 제76권1호
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• pp.141-151
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• 2020

This manuscript tends to investigate influences of nanoscale and surface energy on a static bending and free vibration of piezoelectric perforated nanobeam structural element, for the first time. Nonlocal differential elasticity theory of Eringen is manipulated to depict the long-range atoms interactions, by imposing length scale parameter. Surface energy dominated in nanoscale structure, is included in the proposed model by using Gurtin-Murdoch model. The coupling effect between nonlocal elasticity and surface energy is included in the proposed model. Constitutive and governing equations of nonlocal-surface perforated Euler-Bernoulli nanobeam are derived by Hamilton's principle. The distribution of electric potential for the piezoelectric nanobeam model is assumed to vary as a combination of a cosine and linear variation, which satisfies the Maxwell's equation. The proposed model is solved numerically by using the finite-element method (FEM). The present model is validated by comparing the obtained results with previously published works. The detailed parametric study is presented to examine effects of the number of holes, perforation size, nonlocal parameter, surface energy, boundary conditions, and external electric voltage on the electro-mechanical behaviors of piezoelectric perforated nanobeams. It is found that the effect of surface stresses becomes more significant as the thickness decreases in the range of nanometers. The effect of number of holes becomes significant in the region 0.2 ≤ α ≤ 0.8. The current model can be used in design of perforated nano-electro-mechanical systems (PNEMS).

• Smart Structures and Systems
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• 제17권4호
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• pp.593-610
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• 2016

In this study, an innovative and smart glass fiber-reinforced polymer (GFRP) hybrid bar was developed for stronger durability of concrete structures. As comparing with the conventional GFRP bar, the smart GFRP Hybrid bar can promise to enhance the modulus of elasticity so that it makes the cracking reduced than the case when the conventional GFRP bar is used. Besides, the GFRP Hybrid bar can effectively resist the corrosion of conventional steel bar by the GFRP outer surface on the steel bar. In order to verify the bond performance of the GFRP hybrid bar for structural reinforcement, uniaxial pull-out test was conducted. The variables were the bar diameter and the number of strands and pitch of the fiber ribs. Tensile tests showed a excellent increase in the modulus of elasticity, 152.1 GPa, as compared to that of the pure GFRP bar (50 GPa). The stress-strain curve was bi-linear, so that the ductile performance could be obtained. For the bond test, the entire GFRP hybrid bar test specimens failed in concrete splitting due to higher shear strength resulting in concrete crushing as a function of bar deformation. Investigation revealed that an increase in the number of strands of fiber ribs enhanced the bond strength, and the pitch guaranteed the bond strength of 19.1 mm diameter hybrid bar with 15.9 mm diameter of core section of deformed steel the ACI 440 1R-15 equation is regarded as more suitable for predicting the bond strength of GFRP hybrid bars, whereas the CSA S806-12 prediction is considered too conservative and is largely influenced by the bar diameter. For further study, various geometrical and material properties such as concrete cover, cross-sectional ratio, and surface treatment should be considered.

• 한국도로학회논문집
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• 제9권4호
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• pp.205-213
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• 2007

본 연구에서는 포장용 콘크리트의 강도실험을 통해 강도간의 상관관계식을 도출하는 것을 목적으로 하였다. 강도로서 재령별 압축강도, 휨강도, 할렬인장강도와 탄성계수를 측정하였다. 배합변수는 조골재(화강암, 석회암, 사암), 세골재(자연사, 세척사, 부순모래) 및 단위시멘트량(315-375kg)을 변수로 하였다. 전체적으로 골재나 단위시멘트량보다는 재령에 의해 전형적인 강도곡선을 따라 뚜렷하게 변화함을 보여준다. 이러한 강도결과를 바탕으로 휨강도와 압축강도, 할렬인장강도와 압축강도, 탄성계수와 압축강도, 할렬인장강도와 휨강도의 상관관계를 분석한 결과 휨강도와 압축강도, 탄성계수와 압축강도는 기존의 관례대로 제곱근(n=0.5)의 상관관계식이 잘 맞음을 알 수 있었다. 할렬인장강도와 휨강도는 선형의 상관관계식으로 표현하였고, 할렬인장강도와 압축강도는 n=0.87의 지수승을 사용한 경우가 가장 적합한 것으로 나타났다.

• Advances in nano research
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• 제9권3호
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• pp.157-172
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• 2020

The aim of this present research is the effect of the higher-order terms of the governing equation on the forced longitudinal vibration of a nanorod model and making comparisons of the results with classical nonlocal elasticity theory. For this purpose, the free axial vibration along with forced one under the two various linear and harmonic axial concentrated forces in zigzag Single-Walled Carbon Nanotube (SWCNT) are analyzed dynamically. Three various theories containing the classical theory, which is called Eringen's nonlocal elasticity, along with Rayleigh and Bishop theories (higher-order theories) are established to justify the nonlocal behavior of constitutive relations. The governing equation and the related boundary conditions are derived from Hamilton's principle. The assumed modes method is adopted to solve the equation of motion. For the free axial vibration, the natural frequencies are calculated for the various values of the nonlocal parameter only based on Eringen's theory. The effects of the nonlocal parameter, thickness, length, and ratio of the excitation frequency to the natural frequency over time in dimensional and non-dimensional axial displacements are investigated for the first time.

• 한국주거학회논문집
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• 제22권6호
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• pp.51-60
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• 2011

The maintenance cost depends on various factors such as building volume, floor area, number of household and so on. The maintenance cost of the apartment housing is affected by the maintenance type, building physical factor, sociogeographic aspects. Among these, the maintenance characteristics is represented and made up by the total floor area and number of household which means main factor to provide the building scale roughly. In this paper, it aimed at modelling the estimation function of the maintenance cost with the total floor area and number of household and analyzing the elasticity of the two factors. Although items of maintenance cost are various in general cost, repair cost and so on, we classified these items into the 5 categories. 5 categories are a general cost, a facility maintenance cost, a utilization cost, insurance and sanitary cost. The estimation function used a power function and it has better goodness-offitness than any other estimation methods in statistics. A power function has a three curve types with concave and convex and linear style to the origin.

• Structural Engineering and Mechanics
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• 제61권6호
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• pp.721-736
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• 2017

In this paper, free vibration characteristics of functionally graded (FG) nanobeams embedded on elastic medium are investigated based on third order shear deformation (Reddy) beam theory by presenting a Navier type solution for the first time. The material properties of FG nanobeam are assumed to vary gradually along the thickness and are estimated through the power-law and Mori-Tanaka models. A two parameters elastic foundation including the linear Winkler springs along with the Pasternak shear layer is in contact with beam. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. The nonlocal equations of motion are derived based on third order shear deformation beam theory through Hamilton's principle and they are solved applying analytical solution. According to the numerical results, it is revealed that the proposed modeling can provide accurate frequency results of the FG nanobeams as compared to some cases in the literature. The obtained results are presented for the vibration analysis of the FG nanobeams such as the influences of foundation parameters, gradient index, nonlocal parameter and slenderness ratio in detail.