• Steel and Composite Structures
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• 제20권4호
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• pp.889-911
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• 2016

Using the hyperbolic shear deformation plate model and including plate-foundation interaction (Winkler and Pasternak model), an analytical method in order to determine the deflection and stress distributions in simply supported rectangular functionally graded plates (FGP) subjected to a sinusoidal load, a temperature and moisture fields. The present theory exactly satisfies stress boundary conditions on the top and the bottom of the plate. No transversal shear correction factors are needed because a correct representation of the transversal shearing strain is given. Materials properties of the plate (elastic, thermal and moisture expansion coefficients) are assumed to be graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. Numerical examples are presented and discussed for verifying the accuracy of the present theory in predicting the bending response of FGM plates under sinusoidal load and a temperature field as well as moisture concentration. The effects of material properties, temperature, moisture, plate aspect ratio, side-to-thickness ratio, ratio of elastic coefficients (ceramic-metal) and three distributions for both temperature and moisture on deflections and stresses are investigated.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.650-654
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• 1995

In this study, in order to measure energy-absorbing charactistics in collapse test of CFRP thin-walled laminates and interpretate the cause of decreasing age when collapse test is carried out under the environments of high temperatures and hygrothermals, the moisture absorbing behavior according to the variety of orientation angel is observed and collapse characteristics is compared with the influence of high temperatures and hygrothermals. Especially, we supposed to clearly understand reationship between collapse characteristics in proportion to the variety of orientation angel and moisture absorbing. The value of the maximum loading, mean loading,rate of energy absorption energy per unit volume and mass in CFRP thin-walled laminates on the high temperatures and hygrothermals is measured lower than under no moisture absorbing. The maximum collapse loading in dynamic impact test is taken measurement lower than in static collapse test regarding compared with collapse characteristics conformity with the variety of the CFRP circular laminates in high temperatures and hygrothermals. But the absorbed energy per unit mass and volume is almost same and the biggest amount of energy is shown in the CFRP circular laminates with orientation angel of 15 .deg.. Therefore, in the case of use to CFRP circular laminates with axisymmetric mode, CFRP thin-walled structal members with orientation angel of 10 .deg. , 15 . deg. are generally useful.

• Steel and Composite Structures
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• 제28권1호
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• pp.99-110
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• 2018

In this paper, a new size-dependent quasi-3D plate theory is presented for wave dispersion analysis of functionally graded nanoplates while resting on an elastic foundation and under the hygrothermaal environment. This quasi-3D plate theory considers both thickness stretching influences and shear deformation with the variations of displacements in the thickness direction as a parabolic function. Moreover, the stress-free boundary conditions on both sides of the plate are satisfied without using a shear correction factor. This theory includes five independent unknowns with results in only five governing equations. Size effects are obtained via a higher-order nonlocal strain gradient theory of elasticity. A variational approach is adopted to owning the governing equations employing Hamilton's principle. Solving analytically via Fourier series, these equations gives wave frequencies and phase velocities as a function of wave numbers. The validity of the present results is examined by comparing them with those of the known data in the literature. Parametric studies are conducted for material composition, size dependency, two parametric elastic foundation, temperature and moisture differences, and wave number. Some conclusions are drawn from the parametric studies with respect to the wave characteristics.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.603-608
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• 2004

The paper analyzes a scheme of decontamination of radionuclides from concrete structures, in which rapid microwave heating is used to spall off a thin contaminated surface layer. The analysis is split in two parts: (1) The hygrothermal part of the problem, which consists in calculating the evolution of the temperature and pore pressure fields, and (2) the fracturing part, which consists in predicting the stresses, deformations and fracturing. The rate of the distributed source of heat due to microwaves in concrete is calculated on the basis of the standing wave normally incident to the concrete wall with averaging over both the time period and the wavelength because of the very short time period of microwaves compared to the period of temperature waves and the heterogeneity of concrete. The reinforcing bars parallel to the surface arc treated as a smeared steel layer. The microplane model M4 is used as the constitutive model for nonlinear deformation and distributed fracturing of concrete. The aim of this study is to determine the required microwave power and predict whether and when the contaminated surface layer of concrete spalls off. The effects of wall thickness, reinforcing bars, microwave frequencies and power are studied numerically. As a byproduct of this analysis, the mechanism of spalling of rapidly heated concrete is clarified.

• Advances in nano research
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• 제15권2호
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• pp.175-189
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• 2023

The under-evaluation structure includes a functionally graded porous (FGP) core which is confined by two piezoelectric carbon nanotubes reinforced composite (CNTRC) layers. The whole structure rests on the Pasternak foundation. Using quasi-3D hyperbolic shear deformation theory, governing equations of a sandwich plate are driven. Moreover, face sheets are subjected to the electric field and the whole model is under thermal loading. The properties of all layers alter continuously along with thickness direction due to the CNTs and pores distributions. By conducting the current study, the results emerged in detail to assess the effects of different parameters on buckling of structure. As instance, it is revealed that highest and lowest critical buckling load and consequently stiffness, is due to the V-A and A-V CNTs dispersion type, respectively. Furthermore, it is revealed that by porosity coefficient enhancement, critical buckling load and consequently, stiffness reduces dramatically. Current paper results can be used in various high-tech industries as aerospace factories.

• 터널과지하공간
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• 제26권3호
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• pp.212-219
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• 2016

뿜칠 방수 멤브레인은 숏크리트 사이에 시공되어 라이닝 크랙을 통한 누수를 방지하는 목적으로 최근 유럽 국가를 중심으로 시공 사례가 늘어가고 있다. 뿜칠 방수 멤브레인은 방수 시트에 비해 복잡한 단면에도 시공이 용이하기 때문에 이용 사례가 늘어갈 것으로 전망된다. 뿜칠 방수 멤브레인은 폴리머로 구성된 재료로서 투수성이 매우 낮지만 수분의 이동에 의해 포화가 되고 이로인해 콘크리트 재료에 간극수압이나 동결 문제를 일으킬 수 있는 우려가 있다. 본 연구에서는 뿜칠 방수 멤브레인의 수분이동과 계절변화를 고려하여 숏크리트 라이닝의 열-습도 전달 장기 해석을 수행하였다. 해석을 통해 뿜칠 방수 멤브레인의 수분 흡수 작용과 수분 이동으로 인한 상대습도 변화를 고찰할 수 있었으며 이로 인한 장기적 변화를 모사할 수 있었다.

• Steel and Composite Structures
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• 제39권5호
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• pp.631-643
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• 2021

The aim of this work is to study the hygro-thermo-mechanical bending responses of simply supported FG plate resting on a Winkler-Pasternak elastic foundation. The effect transverse shear strains is taken into account in which the zero transverse shear stress condition on the top and bottom surfaces of the plate is ensured without using any shear correction factors. The developed model contains only four unknowns variable which is reduced compared to other HSDTs models. The material properties of FG-plate are supposed to vary across the thickness of the plate according to power-law mixture. The differential governing equations are derived based on the virtual working principle. Numerical outcomes of bending analysis of FG plates under hygro-thermo-mechanical loads are performed and compared with those available in the literature. The effects of the temperature, moisture concentration, elastic foundation parameters, shear deformation, geometrical parameters, and power-law-index on the dimensionless deflections, axial and transverse shear stresses of the FG-plate are presented and discussed.

• Composites Research
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• 제31권3호
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• pp.88-93
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• 2018

본 연구에서는 입자크기가 서로 다른 할로이사이트 나노튜브(Halloysite nanotube, HNT)와 밀드 카본(Milled carbon, MC) 강화 복합재료를 사용하여 손상된 복합재료 적층판을 계단형 패치 보수법에 따라 수리하고, 손상된 면과 수리면 사이의 접합 계면에 입자가 미치는 기계적, 구조적 영향을 분석하였다. 이 때, 고온고습의 가혹한 수분 환경에 장시간 노출시켜 손상된 판을 형성하는 기존 재료와의 상대적인 재료 물성 회복률을 비교하였으며 기계적 물성 시험을 통해 성능평가를 실시하였다. 그 결과 $70^{\circ}C$ 고온 증류수에서 HNT는 입자 첨가량에 따라 흡습률이 MC에 비해 뚜렷한 차이를 보였으며 인장강도와 굽힘강도의 경우, 대체적으로 HNT로 강화된 복합재를 사용하여 보수한 시험편이 흡습 전과 후 모두 높은 수치를 나타냈다. 특히, 0.5, 1 wt. %의 HNT가 첨가되었을 때 흡습률이 가장 적었고 이는 기계적 강도 증가에 관여하는 하나의 요인으로 작용하였다. 반면 MC는 소량만으로도 높은 흡습 저항성을 나타냈으며 하중의 방향에 따라 강도의 차이가 발생했다.

• Journal of the Korean Wood Science and Technology
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• 제40권1호
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• pp.10-18
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• 2012

최근 만들어지고 있는 거주공간은 단열성능 향상을 통한 냉난방 에너지 절약을 위하여 더욱 기밀해지고 있다. 이로 인해 일상생활 중에 발생하는 수분의 인위적인 배출과 외부공기의 인위적인 유입이 줄어듦에 따라 건축내장재의 자연조습기능에 대한 관심이 증대하고 있다. 본 연구에서는 열처리된 잣나무의 흡 방습성능을 평가하고 이에 영향을 미치는 인자들을 분석하였다. 상대습도 변화에 따른 평형함수율과 흡 방습률을 측정하였고, 조도(거칠기)와 미시적 표면형상, 그리고 FT-IR spectrum과 흡방습성과의 관계를 고찰하였다. 본 연구결과는 거주공간의 조습성능 정량화 평가시스템 구축을 위한 기초자료로 활용될 수 있을 것이라 기대된다.