• Advances in nano research
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• 제4권2호
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• pp.65-84
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• 2016

This paper investigates the buckling behavior of shear deformable piezoelectric (FGP) nanoscale beams made of functionally graded (FG) materials embedded in Winkler-Pasternak elastic medium and subjected to an electro-magnetic field. Magneto-electro-elastic (MEE) properties of piezoelectric nanobeam are supposed to be graded continuously in the thickness direction based on power-law model. To consider the small size effects, Eringen's nonlocal elasticity theory is adopted. Employing Hamilton's principle, the nonlocal governing equations of the embedded piezoelectric nanobeams are obtained. A Navier-type analytical solution is applied to anticipate the accurate buckling response of the FGP nanobeams subjected to electro-magnetic fields. To demonstrate the influences of various parameters such as, magnetic potential, external electric voltage, power-law index, nonlocal parameter, elastic foundation and slenderness ratio on the critical buckling loads of the size-dependent MEE-FG nanobeams, several numerical results are provided. Due to the shortage of same results in the literature, it is expected that the results of the present study will be instrumental for design of size-dependent MEE-FG nanobeams.

• Steel and Composite Structures
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• 제50권4호
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• pp.403-418
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• 2024

In this paper, vibration and energy absorption characteristics of a nanostructure which is composed of two embedded porous annular/circular nanoplates coupled by a viscoelastic substrate are investigated. The modified couple stress theory (MCST) and the Gurtin-Murdoch theory are applied to take into account the size and the surface effects, respectively. Furthermore, the structural damping effect is probed by the Kelvin-Voigt model and the mathematical model of the problem is developed by a new hyperbolic higher order shear deformation theory. The differential quadrature method (DQM) is employed to obtain the out-of-phase and in-phase frequencies of the structure in order to predict the dynamic response of it. The acquired results reveal that the vibration and energy absorption of the system depends on some factors such as porosity, surface stress effects, material length scale parameter, damping and spring constants of the viscoelastic foundation as well as geometrical parameters of annular/circular nanoplates. A bird's-eye view of the findings in the research paper offers a comprehensive understanding of the vibrational behavior and energy absorption capabilities of annular/circular porous nanoplates. The multidisciplinary approach and the inclusion of porosity make this study valuable for the development of innovative materials and applications in the field of nanoscience and engineering.

• Computers and Concrete
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• 제33권1호
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• pp.91-102
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• 2024

Beam-shaped components commonly rotate along a fixed axis when massive mechanical structures like rotors, jet engine blades, motor turbines, and rotating railway crossings perform their functions. For these structures to be useful in real life, their mechanical behavior is essential. Therefore, this is the first article to use the modified shear deformation theory type hyperbolic sine functions theory and the FEM to study the static bending response of rotating functionally graded GPL-reinforced composite (FG-GPLRC) beams with initial geometrical deficiencies in thermal media. Graphene platelets (GPLs) in three different configurations are woven into the beam's composition to increase its strength. By comparing the numerical results with those of previously published studies, we can assess the robustness of the theory and mechanical model employed in this study. Parameter studies are performed to determine the effect of various geometric and physical variables, such as rotation speed and temperature, on the bending reactions of structures.

• Advances in nano research
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• 제16권3호
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• pp.313-324
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• 2024

The main aims of this study are to develop a new nonlocal quasi-3D theory for the free vibration behaviors of the functionally graded sandwich nanobeams. The sandwich beams consist of a ceramic core and two functionally graded material layers resting on elastic foundations. The two layers, linear spring stiffness and shear layer, are used to model the effects of the elastic foundations. The size-effect is considered using nonlocal elasticity theory. The governing equations of the motion of the functionally graded sandwich nanobeams are obtained via Hamilton's principle in combination with nonlocal elasticity theory. Then the Navier's solution technique is used to solve the governing equations of the motion to achieve the nonlocal free vibration behaviors of the nanobeams. A deep parametric study is also provided to demonstrate the effects of some parameters, such as length-to-height ratio, power-law index, nonlocal parameter, and two parameters of the elastic foundation, on the free vibration behaviors of the functionally graded sandwich nanobeams.

• Smart Structures and Systems
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• 제26권3호
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• pp.331-343
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• 2020

In this paper, based on the CPT, motion equations for a sandwich plate containing a core and two integrated face-sheets have derived. The structure rests on the Visco-Pasternak foundation, which includes normal and shear modules. The piezo-magnetic core is made of CoFe₂O₄ and also is subjected to 3D magnetic potential. Two face sheets at top and bottom of the core are under electrical fields. Also, in order to obtain more accuracy, the effect of flexoelectricity has took into account at face sheets' relations in this work. Flexoelectricity is a property of all insulators whereby they polarize when subject to an inhomogeneous deformation. This property plays a crucial role in small-scale rather than macro scale. Employing CPT, Hamilton's principle, flexoelectricity considerations, the governing equations are derived and then solved analytically. By present work a detailed numerical study is obtained based on Piezoelectricity, Flexoelectricity and modified couple stress theories to indicate the significant effect of length scale parameter, shear correction factor, aspect and thickness ratios and boundary conditions on natural frequency of sandwich plates. Also, the figures show that there is an excellent agreement between present study and previous researches. These finding can be used for automotive industries, aircrafts, marine vessels and building industries.

• 농업과학연구
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• 제5권1호
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• pp.15-28
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• 1978

흙의 전단강도(剪斷强度) 옹벽(擁壁)이나 사면(斜面)의 안정(安定) 혹은 구조물기초(構造物基礎)의 설계등(設計等)의 문제(問題)를 해결(解決)하는데 중요(重要)한 것으로 알려져 있다. 직접전단시험기(直接剪斷試驗機)는 수직응력(垂直應力)의 불균일성(不均一性), 진행성파괴(進行性破壞), 측면마찰(側面摩擦)의 영향등(影響等)에 대(對)하여 해결(解決)하여야 할 문제(問題)를 내포(內包)하고 있다. 그러나 본시험(本試驗)에서는 그의 장치(裝置)가 간편(簡便)하여 널리 사용(使用)되고 있는 직접전단시험기(直接剪斷試驗機)를 사용(使用)하여 밀도(密度)와 함수비(含水比)를 변화(變化)시키면서 비배수(非排水) 급속전단시험(急速剪斷試驗)을 하여 다음과 같은 결과(結果)를 얻었다. 1. 건조밀도(乾燥密度)가 증가(增加)함에 딸라 전단강도(剪斷强度)는 큰 값을 나타내고 같은 밀도(密度)에서도 입도배합(粒度配合)이 양호(良好)한 흙에서 전단강도(剪斷强度)는 큰 값을 나타냈다. 2. 점착력(粘着力)은 건조밀도(乾燥密度)가 커짐에 따라 증가(增加)하는 경향(傾向)을 나타냈으나 내부마찰각(內部摩擦角)은 일률적(一律的)인 증가(增加)의 경향(傾向)이 나타나지 않았다. 3. 함수비(含水比)가 증가(增加)함에 따라 전단강도(剪斷强度)는 감소(減少)하였고 이와같은 현상(現象)은 입도배합(粒度配合)이 양호(良好)한 흙에서 더욱 현저하게 나타났다. 4. 점착력(粘着力)은 흙의 함수비(含水比)가 최적함수비(最適含水比)에 가까울 때 최대(最大)로 되고, 내부마찰각(內部摩擦角) 함수비(含水比)가 증가(增加)함에 따라 감소(減少)하였다. 이와같은 현상(現象)은 입도배합(粒度配合)이 양호(良好)한 SDC-1 시료(試料)에서 더욱 현저하게 나타났다. 5. 점착력(粘着力)은 공극비(空隙比)가 증가(增加)함에 따라 감소(減少)하였고 내부마찰각(內部摩擦角)은 이와 같은 경향(傾向)이 나타나지 않았다.

• 한국지반공학회논문집
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• 제27권9호
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• pp.67-76
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• 2011

동토지역 말뚝기초의 지지력은 말뚝과 토사의 접촉면에서 작용하는 동착강도에 지배된다. 말뚝주변 토사 내 간극수의 동결로 인해 발현되는 동착강도는 동토지반 기초설계에 있어 가장 주요한 설계정수로 고려되고 있다. 지난 50년간 동착강도에 대한 연구가 다각도로 수행되어 왔으나, 대부분 동결온도와 지중온도를 고정조건으로 그 영향력을 고려하지 않은 채 토사종류, 말뚝종류, 재하속도 등의 영향인자를 분석하기 위한 목적으로 수행되었다. 본 연구에서는 동결온도와 마찰면에 작용하는 수직구속응력을 주요 변수로 적용하고, 토사종류, 말뚝종류, 재하속도 등은 고정조건으로 적용하여 직접전단방식의 동착강도 측정실험을 수행하였다. 실험재료로는 표면 가공이 용이하여 거칠기를 정밀하게 조절할 수 있는 알루미늄 모형과 주문진표준사를 활용하였다. 실험은 상온(> $0^{\circ}C$), $-1^{\circ}C$, $-2^{\circ}C$, $-5^{\circ}C$, $-10^{\circ}C$의 동결온도및 1atm, 2atm, 3atm의 수직구속응력 조건에서 수행되었으며, 그 결과를 바탕으로 동결온도와 수직구속응력이 동착강도에 미치는 영향을 분석하였다. 전반적으로 동착강도는 동결온도가 낮아질수록, 혹은 수직구속응력이 커질수록 증가하는 경향을 보였으며, 특히 단위온도차에 따른 동착강도의 증가율이 1)급증하는 구간과 2)점진적으로 감소하는 구간을 뚜렷하게 나타내며 변화하는 특성을 보였다. 또한, 동결온도의 저하에 따라 동착강도의 변화를 지배하는 요소가 마찰각에서 부착력으로 변화하며 수렴구간을 형성하는 경향을 나타냈다.