• 한국지반공학회논문집
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• 제18권5호
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• pp.55-65
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• 2002

소성흐름을 발생시키는 측방유동 가능지반내에 설치된 매설관에 작용하는 토압에 대한 메카니즘을 규명하기 위해 파괴형상실험을 실시하고, 파괴형상실험을 토대로 지반변형속도를 고려하기 위해 Maxwell 점탄성 모델을 적용한 토압산정식을 제안하였다. 직접전단실험으로 구한 점성계수와 내부마찰각과 상재압을 고정하여 이론식으로 도출해낸 점성계수가 잘 일치하고 있음을 확인하였고 모형실험결과와 이론식에 의한 토압은 지반변형속도에 영향을 받으며 비교적 일치하며 지반변형이 없는 경우에도 정지토압을 받음을 알 수 있다. 또한, 지반의 지지력은 점성토에서는 관입전단파괴시의 값과 거의 일치하였다. 또한, 매설관 주변지반의 파괴모드는 매설관직경과 무관하게 지반변형속도에 영향을 받으며 작용토압은 균질한 지층의 경우 선형적으로 증가하고 조립질에 가까울수록 선형적 감소치를 보이므로 매설관주변지반의 매립재를 이용하여 매설관주변의 토압을 경감시킬 수 있음을 알 수 있다.

• Steel and Composite Structures
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• 제46권6호
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• pp.839-856
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• 2023

This work presents a simple four-unknown refined integral plate theory for mechanical and thermal buckling behaviors of functionally graded (FG) plates resting on Visco-Pasternak foundations. The proposed refined high order shear deformation theory has a new displacement field which includes indeterminate integral variables and contains only four unknowns in which any shear correction factor not used, with even less than the conventional theory of first shear strain (FSDT). Governing equations are deduced from the principle of minimum total potential energy and a Navier type analytical solution is adopted for simply supported FG plates. The Visco-Pasternak foundations is considered by adding the impact of damping to the usual foundation model which characterized by the linear Winkler's modulus and Pasternak's foundation modulus. The accuracy of the present model is demonstrated by comparing the computed results with those available in the literature. Some numerical results are presented to show the impact of material index, elastic foundation type, and damping coefficient of the foundation, on the mechanical and thermal buckling behaviors of FG plates.

• Computers and Concrete
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• 제7권4호
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• pp.317-329
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• 2010

The paper describes localization of deformation in a bar under tensile loading. The material of the bar is considered as non-linear viscous elastic and the bar consists of two symmetric halves. It is assumed that the model represents behavior of the quasi-brittle viscous material under uniaxial tension with different loading rates. Besides that, the bar could represent uniaxial stress-strain law on a single plane of a microplane material model. Non-linear material property is taken from the microplane material model and it is coupled with the viscous damper producing non-linear Maxwell material model. Mathematically, the problem is described with a system of two partial differential equations with a non-linear algebraic constraint. In order to obtain solution, the system of differential algebraic equations is transformed into a system of three partial differential equations. System is subjected to loadings of different rate and it is shown that localization occurs only for high loading rates. Mathematically, in such a case two solutions are possible: one without the localization (unstable) and one with the localization (stable one). Furthermore, mass is added to the bar and in that case the problem is described with a system of four differential equations. It is demonstrated that for high enough loading rates, it is the added mass that dominates the response, in contrast to the viscous and elastic material parameters that dominated in the case without mass. This is demonstrated by several numerical examples.

• 한국자동차공학회논문집
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• 제8권4호
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• pp.149-157
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• 2000

Computer simulations of the mechanical behavior of a three point bend specimen with a quarter notch under impact load are performed. The case with a load application point at the side is considered. An elastic-plastic von Mises material model is chosen. Three phases such as impact bouncing and bending phases are found to be identified during the period from the moment of impact to the estimated time for crack initiation. It is clearly shown that no plastic deformation near the crack tip is appeared at the impact phase. However it is confirmed that the plastic zone near the crack tip emerges in the second phase and the plastic hinge has been formed in the third phase. Gap opening displacement crack tip opening displacement and strain rate are compared with rate dependent material(visco-plastic material). The stability during various dynamic load can be seen by using the simulation of this study.

• Smart Structures and Systems
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• 제20권5호
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• pp.583-593
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• 2017

This research deals with the nonlocal temperature-dependent dynamic buckling analysis of embedded sandwich micro plates reinforced by functionally graded carbon nanotubes (FG-CNTs). The material properties of structure are assumed viscoelastic based on Kelvin-Voigt model. The effective material properties of structure are considered based on mixture rule. The elastic medium is simulated by orthotropic visco-Pasternak medium. The motion equations are derived applying Sinusoidal shear deformation theory (SSDT) in which the size effects are considered using Eringen's nonlocal theory. The differential quadrature (DQ) method in conjunction with the Bolotin's methods is applied for calculating resonance frequency and dynamic instability region (DIR) of structure. The effects of different parameters such as volume percent of CNTs, distribution type of CNTs, temperature, nonlocal parameter and structural damping on the dynamic instability of visco-system are shown. The results are compared with other published works in the literature. Results indicate that the CNTs have an important role in dynamic stability of structure and FGX distribution type is the better choice.

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.261-273
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• 2017

The control of the deformative behaviour of pre-stressed concrete roof elements for a satisfactory service performance is a main issue of their structural design. Slender light-weight wing-shaped roof elements, typical of the European heritage, are particularly sensitive to this problem. The paper presents the results of deformation measurements during storage and of both torsional-flexural and purely flexural load tests carried out on a full-scale 40.5 m long innovative wing-shaped roof element. An element-based simplified integral procedure that de-couples the evolution of the deflection profile with the progressive shortening of the beam is adopted to catch the experimental visco-elastic behaviour of the element and the predictions are compared with normative close-form solutions. A linear 3D fem model is developed to investigate the torsional-flexural behaviour of the member. A mechanical non-linear beam model is used to predict the purely flexural behaviour of the roof member in the pre- and post-cracking phases and to validate the loss prediction of the adopted procedure. Both experimental and numerical results highlight that the adopted analysis method is viable and sound for an accurate simulation of the service behaviour of precast roof elements.

• Steel and Composite Structures
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• 제24권4호
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• pp.499-512
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• 2017

This paper deals with nonlinear dynamic stability of embedded piezoelectric nano-composite separators conveying pulsating fluid. For presenting a realistic model, the material properties of structure are assumed viscoelastic based on Kelvin-Voigt model. The separator is reinforced with single-walled carbon nanotubes (SWCNTs) which the equivalent material properties are obtained by mixture rule. The separator is surrounded by elastic medium modeled by nonlinear orthotropic visco Pasternak foundation. The separator is subjected to 3D electric and 2D magnetic fields. For mathematical modeling of structure, three theories of classical shell theory (CST), first order shear deformation theory (FSDT) and sinusoidal shear deformation theory (SSDT) are applied. The differential quadrature method (DQM) in conjunction with Bolotin method is employed for calculating the dynamic instability region (DIR). The detailed parametric study is conducted, focusing on the combined effects of the external voltage, magnetic field, visco-Pasternak foundation, structural damping and volume percent of SWCNTs on the dynamic instability of structure. The numerical results are validated with other published works as well as comparing results obtained by three theories. Numerical results indicate that the magnetic and electric fields as well as SWCNTs as reinforcer are very important in dynamic instability analysis of structure.

• Advances in aircraft and spacecraft science
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• 제6권3호
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• pp.257-272
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• 2019

Numerical study of the flutter of a plate on a viscoelastic foundation is carried out in the paper. Critical velocity of the flutter of a plate on an elastic and viscoelastic foundation is determined. The mathematical model for the investigation of viscoelastic plates is based on the Marguerre's theory applied to the study of the problems of strength, rigidity and stability of thin-walled structures such as aircraft wings. Aerodynamic pressure is determined in accordance with the A.A. Ilyushin's piston theory. Using the Bubnov - Galerkin method, the basic resolving systems of nonlinear integro-differential equations (IDE) are obtained. At wide ranges of geometric and physical parameters of viscoelastic plates, their influence on the flutter velocity has been studied in detail.

• 한국농공학회지
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• 제45권4호
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• pp.137-143
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• 2003

The initial condition of $\Delta \sigma_3 \;=\; \Delta u$ is used for analyzing the time dependent behavior of ground. This is based on the concept that the coefficient of pore water B is the unity on the condition of saturation. but some measured consolidation data in the field showed that the pore water pressure was not dissipated as time elapsed but it was maintained constant value or it's dissipation rate was slower than that of the predicted. and so the measured data of pore water pressure was not consistent with that of settlement. In this study, the rheological model for the pore water pressure behavior on undrained condition was induced and compared with the experiment data of the literature. The result showed that the suggested model was consistent well with the result of experiment, but the suggested model could not explain the effect of the decrease of void ratio according to consolidation.

• 농업과학연구
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• 제23권2호
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• pp.233-241
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• 1996

The mechanical properties of biological materials depend on numerous factors. The majority of these relationships are still unknown today, especially with regard to their quantitative characteristics. The reason is that biological materials constitute biomechanical systems of very complex construction, whose behavior cannot be characterized by simple physical constants, as for example can that of engineering materials. The objectives of this investigation were to determine the compression creep and recovery properties of rice stalks at various levels of applied load The compression creep and recovery behavior of the rice stalk could be predicted precisely by rheological model which approached closely to the measured values. But the coefficients of the Burgers recovery model were different from those of the creep model. The Steady state creep behavior occurred at the higher level of force and the logarithmic creep behavior occurred at the lower level of force. The mechanical model being expected the creep behavior in relation with the level of applied load, which was well explained that the rice stalk might be visco-elastic material.