• Advances in aircraft and spacecraft science
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• 제3권4호
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• pp.471-502
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• 2016

This paper presents the dynamic instability analysis of un-damped elastically supported piezoelectric functionally graded (FG) beams subjected to in-plane static and dynamic periodic thermomechanical loadings with uncertain system properties. The elastic foundation model is assumed as one parameter Pasternak foundation with Winkler cubic nonlinearity. The piezoelectric FG beam is subjected to non-uniform temperature distribution with temperature dependent material properties. The Young's modulus and Poison's ratio of ceramic, metal and piezoelectric, density of respective ceramic and metal, volume fraction exponent and foundation parameters are taken as uncertain system properties. The basic nonlinear formulation of the beam is based on higher order shear deformation theory (HSDT) with von-Karman strain kinematics. The governing deterministic static and dynamic random instability equation and regions is solved by Bolotin's approach with Newmark's time integration method combined with first order perturbation technique (FOPT). Typical numerical results in terms of the mean and standard deviation of dynamic instability analysis are presented to examine the effect of slenderness ratios, volume fraction exponents, foundation parameters, amplitude ratios, temperature increments and position of piezoelectric layers by changing the random system properties. The correctness of the present stochastic model is examined by comparing the results with direct Monte Caro simulation (MCS).

• Earthquakes and Structures
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• 제10권5호
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• pp.1033-1048
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• 2016

An analytical solution based on the neutral surface concept is developed to study the free vibration behavior of simply supported functionally graded plate reposed on the elastic foundation by taking into account the effect of transverse shear deformations. No transversal shear correction factors are needed because a correct representation of the transversal shearing strain obtained by using a new refined shear deformation theory. The foundation is described by the Winkler-Pasternak model. The Young's modulus of the plate is assumed to vary continuously through the thickness according to a power law formulation, and the Poisson ratio is held constant. The equation of motion for FG rectangular plates resting on elastic foundation is obtained through Hamilton's principle. Numerical examples are provided to show the effect of foundation stiffness parameters presented for thick to thin plates and for various values of the gradient index, aspect and side to thickness ratio. It was found that the proposed theory predicts the fundamental frequencies very well with the ones available in literature.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1297-1302
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• 2007

It is very important to evaluate the reliable deformational characteristics of soils not only in the analysis of geotechnical structures under working stress conditions as foundation in railroad or road system but also for the soil dynamic problems. Different testing techniques are likely to have different testing conditions as strain amplitude, stress level, loading frequency and number of loading cycles. The deformational characteristics of soils can be affected by these variables. In this paper, the effects on modulus of soils subjected to cyclic load were investigated. For the evaluation of deformational characteristics of soils subjected cyclic load, various testing such as TS, RC, TX, and FFRC tests were performed. It was shown that the modulus evaluated by various testing methods are comparable to each other fairly well when the effects of these factors were properly taken into account. For reliable evaluation, therefore, those effects on the modulus need to be considered, and measured values should be effectively adjusted to actual conditions where the soil is working.

• Advances in Computational Design
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• 제8권1호
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• pp.77-96
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• 2023

Calculating size-dependent mechanical properties of the nano-scale materials usually involves cumbersome numerical and theoretical works. In this paper, we aim to present a closed-form relation to calculate the length-dependent Young's modulus of carbon nanotubes (CNTs) based on nonlocal elasticity theory. In this regard, a single wall carbon nanotube (SWCNT) is considered as a rod structure and the governing nonlocal equations are developed under uniaxial tensile load. The equations are solved using analytical methods and strain distribution, total displacement and the size-dependent equivalent Young's modulus are obtained. Further, the results are compared with the molecular dynamics results from the literature. The outcome indicates that the calculated relations are coincident with the molecular dynamics results.

• Geomechanics and Engineering
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• 제32권1호
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• pp.21-34
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• 2023

In order to analyze the effect of the cyclic lateral loading on the response of a pile-soil system, a full-scale single steel pile was subjected to one-way cyclic loading. The test pile was driven into a bi-layered soil consisting of a normally consolidated saturated clay overlying a silty sandy layer, the site being submerged by water up to one meter above the mudline in order to reproduce the conditions of an offshore pile foundation. The aim of this paper is to present the main results of interpretation of the cyclic lateral tests in terms of pile deflections, bending moment, and cyclic P-Y curves. From these latter an absolute secant reaction modulus E_AS,N was derived and a simple calculation model of the test single pile is proposed based on this modulus. Two applications of the proposed model are carried out, one with a 2D finite element modelling, and the second with a load transfer curves-based method.

• 한국도로학회논문집
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• 제10권1호
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• pp.63-74
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• 2008

교통하중하의 포장구조체에 대한설계나 비선형해석에 있어 도로하부재료의 회복변형특성이 활용되고 있으나 국내에서는 관련연구가 매우 미진한 실정이다. 또한 매우 제한적인 범위의 자료만이 회복탄성계수를 추정하는데 활용되고 있어 본 연구에서는 도로기초 지반재료인 보조기층과 노상토를 대상으로 비선형특성을 파악하기 위한 반복재하 회복탄성계수 시험을 실시하였다. 또한 이를 토대로 응력조건을 고려한 회복탄성계수 예측모델과 적합한 응력의존 모델을 결정하고 이를 이용하여 유한요소 해석방법을 활용하여 포장체 및 도로하부 지반재료에 대한 거동을 파악하였다.

• Structural Engineering and Mechanics
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• 제63권1호
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• pp.65-76
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• 2017

This research investigated the vibration frequency of sandwich plate made of piezoelectric fiber reinforced composite core (PFRC) and face sheets of piezomagnetic materials. The effective electroelastic constants for PFRC materials are obtained by the micromechanical approach. The resting medium of sandwich plate is modeled by Pasternak foundation including normal and shear modulus. Besides, sandwich plate is subjected to linearly varying normal stresses that change by load factor. The coupled equations of motion are derived using first order shear deformation theory (FSDT) and energy method. These equations are solved by differential quadrature method (DQM) for simply supported boundary condition. A detailed numerical study is carried out based on piezoelectricity theory to indicate the significant effect of load factor, volume fraction of fibers, modulus of elastic foundation, core-to-face sheet thickness ratio and composite materials on dimensionless frequency of sandwich plate. These findings can be used to aerospace, building and automotive industries.

• 한국강구조학회 논문집
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• 제13권5호
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• pp.443-455
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• 2001

전단 층을 갖는 2개 매개변수 탄성지반 위에 놓인 복합재료 적층판에서 휨 진동 및 좌굴해석을 위해 에너지 방법을 사용해 탄성해를 구하였다. 복합재료 적층판의 점탄성 해석은 유사-탄성방법을 사용해 탄성해를 구하였다. 전단에 의한 효과는 3창 전단변형이론을 적용하여 고려하였다. 유도된 식들을 검증하기 위해 LUSAS 프로그램에 의한 탄성지반위에 놓인 이방성 판의 처짐과 비교하였다. 점탄성 휨 진동 및 좌굴해석에 관한 수치해석결과들은 적층순서, 적층 수 재료 비등방성과 전단지반계수 등에 따른 효과를 보여 준다.

• 전산구조공학
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• 제11권1호
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• pp.227-235
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• 1998

임의의 단면과 임의의 경계조건을 갖는 구조요소에 대한 진동해석 방법은 1974년 D.H.Kim에 의해 제시되었다. 이 방법은 복합적층판을 포함한 2차원 문제의 1차모드 진동해석으로 확장하였다. passive와 active 제어 장치를 가지는 빌딩슬래브는 탄성지지된 것과 같이 거동한다. 이 논문에서는 표제의 문제를 해결하기 위하여 이 방법을 사용하였으며, 진동해석에 필요한 처짐 영향면을 유한 차분법을 사용하여 구하였다. 고유 진동수에 대한 슬래브 강성-기초탄성계수의 상대적인 값의 영향을 고찰하였다.

• Steel and Composite Structures
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• 제23권6호
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• pp.657-668
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• 2017

In the most of previous studies, researchers have restricted their own studies to consider the effect of single walled carbon nanotubes as a reinforcement on the vibrational behavior of structures. In the present work, free vibration characteristics of functionally graded annular plates reinforced by multi-walled carbon nanotubes resting on Pasternak foundation are presented. The response of the elastic medium is formulated by the Winkler/Pasternak model. Modified Halpin-Tsai equation was used to evaluate the Young's modulus of the multi-walled carbon nanotube/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. The exponential shape factor modifies the Halpin-Tsai equation from expressing a straight line to a nonlinear one in the multi-walled carbon nanotubes wt% range considered. The 2-D generalized differential quadrature method as an efficient and accurate numerical tool is used to discretize the equations of motion and to implement the various boundary conditions. The effects of two-parameter elastic foundation modulus, geometrical and material parameters together with the boundary conditions on the frequency parameters of the plates are investigated. This study serves as a benchmark for assessing the validity of numerical methods or two-dimensional theories used to analysis of annular plates.