• Structural Engineering and Mechanics
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• 제22권5호
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• pp.599-611
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• 2006

The theory with hierarchical warping functions had been used to analyze composite thin-walled structure, laminated beam and had good results. In the present paper, a series of hierarchical warping functions are developed to analyze the cylindrical bending problems of composite lamina. These warping functions which refine through-the-thickness variation of displacements were composed of basic and corrective functions by taking into account of anisotropic, material discontinues, and transverse shear and normal strain. Then the hierarchical finite element method was used to form a numerical algorithm. The distribution of the displacements, in-plane stresses, transverse shear stresses and transverse normal stress for composite laminate were analyzed with the present model. The results show that the present model has precise mechanical response compared with the first deformation transverse theory and the corrective order affects the accuracy of result.

• 한국광학회지
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• 제8권5호
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• pp.415-419
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• 1997

광섬유 격자는 외부의 가해진 물리량에 대해 선형적인 응답을 하며, 광섬유 격자의 파장 인코딩 특성으로 인해 S/N비가 높은 신호 처리를 할 수 있는 장점이 있다. 본 논문에서는 편광 유지 광섬유 격자를 이용한 압력 센서에 관한 실험을 수행하였다. 편광 유지 광섬유 격자는 위상 마스크를 이용하여 Bow-Tie형 광섬유에 형성시켰는데, 편광 유지 광섬유는 두 개의 고유 편광 축을 가지므로 두 개의 브래그 peak을 가진다. 종방향 스트레인과 온도 변화에 따른 두 개의 브래그 파장 변화를 측정한 결과 각각 1.2 pm/.mu..epsilon.의 종방향 스트레인에 대한 파장 민감도와 11.4 pm/.deg. C의 온도에 대한 파장 민감도가 관측되어, 단일 모드 광섬유 격자의 보고된 값과 거의 일치하였다. 반면에 편광 유지 광섬유 격자에 횡방향 스트레스를 가하면 두 브래그 파장사이의 간격이 변화함을 관측하였고, 두 브래그 파장 간격에 대하여는 14.6 pm/N의 횡방향 스트레스에 대한 파장 민감도를 얻었다. 편광 유지 광섬유 격자 센서는 온도의 변화에 무관한 횡방향 스트레스 즉, 압력센서로 이용할 수 있음을 보였다.

• Advances in aircraft and spacecraft science
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• 제3권2호
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• pp.113-148
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• 2016

In a whole variety of higher order plate theories existing in the literature no consideration is given to the transverse normal strain / deformation effects on flexural response when these higher order theories are applied to shear flexible composite plates in view of minimizing the number of unknown variables. The objective of this study is to carry out cylindrical bending of simply supported laminated composite and sandwich plates using sinusoidal shear and normal deformation plate theory. The most important feature of the present theory is that it includes the effects of transverse normal strain/deformation. The displacement field of the presented theory is built upon classical plate theory and uses sine and cosine functions in terms of thickness coordinate to include the effects of shear deformation and transverse normal strain. The theory accounts for realistic variation of the transverse shear stress through the thickness and satisfies the shear stress free conditions at the top and bottom surfaces of the plate without using the problem dependent shear correction factor. Governing equations and boundary conditions of the theory are obtained using the principle of minimum potential energy. The accuracy of the proposed theory is examined for several configurations of laminates under various static loadings. Some problems are presented for the first time in this paper which can become the base for future research. For the comparison purpose, the numerical results are also generated by using higher order shear deformation theory of Reddy, first-order shear deformation plate theory of Mindlin and classical plate theory. The numerical results show that the present theory provides displacements and stresses very accurately as compared to those obtained by using other theories.

• Composites Research
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• 제36권2호
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• pp.117-125
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• 2023

본 논문에서는 복합소재 적층 구조물의 열-기계적 거동을 효과적으로 예측할 수 있는 8절점 판 요소 기반 전산해석 기법을 제안하고자 한다. 횡방향 수직 변형이 고려된 개선된 일차전단변형이론을 바탕으로 유한요소 정식화를 수행하였으며, 독립적으로 가정되는 변위장 및 응력장 사이의 타당한 수학적 관계식을 도출함으로써 해석 결과의 정확도와 계산 과정의 효율성을 동시에 향상시키고자 하였다. 또한, 횡 방향 변위장의 개선을 통해 횡 방향 수직 변형을 효과적으로 고려함으로써, 복합소재 적층 구조물의 열적 거동 예측 과정에서의 신뢰성을 확보하고자 하였다. 수치 예제로써 열-기계 하중을 받는 2차원 복합소재 적층평판을 고려하였으며, 3차원 탄성해 및 참고문헌에서 활용 가능한 해석 결과와의 비교, 검토를 통해 제안된 유한요소 해석 기법의 성능을 검증하였다.

• 콘크리트학회논문집
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• 제28권5호
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• pp.527-534
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• 2016

CFRP의 전단강도 기여분을 평가하고, 모어서클을 이용하여 전단거동 특성을 분석하기 위해 전단철근비가 서로 다른 보에 동일한 탄소섬유 전단보강 설계한 보 실험을 수행하였다. 취성특성을 가지는 CFRP의 전단기여분을 평가하기 위해서는 CFRP의 변형률을 평가해야 한다. 각 실험결과는 모어써클(Mohr's Circle)을 활용하여 전단변형률을 주인장변형률 및 균열각도의 변화와 연계하여 비교하였다. 전단철근비가 작은 경우 탄소섬유 자체의 전단강도 기여분 뿐만 아니라 탄소섬유에 의해 콘크리트 균열의 진전을 제어하여 균열에 의한 콘크리트의 성능저하를 최소화한다. 전단철근비가 큰 경우는 전단철근비가 작을 때 보다 탄소섬유 보강효과가 크지 않았다. 따라서 보강부재의 전단성능을 결정할 때 탄소섬유의 전단강도 기여분은 전단철근과의 상호작용을 고려할 수 있는 변형적합조건에 근거하여 평가되어야 한다.

• Structural Engineering and Mechanics
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• 제49권5호
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• pp.661-672
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• 2014

Laminated Rectangular plates embedded in elastic foundations are used in many mechanical structures. This study presents an analytical approach for transverse bending analysis of an embedded symmetric laminated rectangular plate using Mindlin plate theory. The surrounding elastic medium is simulated using Pasternak foundation. Adopting the Mindlin plate theory, the governing equations are derived based on strain-displacement relation, energy method and Hamilton's principle. The exact analysis is performed for this case when all four ends are simply supported. The effects of the plate length, elastic medium and applied force on the plate transverse bending are shown. Results indicate that the maximum deflection of the laminated plate decreases when considering an elastic medium. In addition, the deflection of the laminated plate increases with increasing the plate width and length.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 추계학술발표대회 논문집
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• pp.144-148
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• 2001

A proper estimation of the mechanical properties for composites has been required for better design/selection of constituents for composite materials. Present investigation shows the simulation results for ceramic reinforced metal matrix composite under uniaxial transverse tensile loading. The resulting transverse mean stress with the transverse mean strain was described for composites as a function of the volume fraction with two different types of interfacial bonding: (1)strongly bonded interface, and (2)no bonded interface. A two-dimensional finite element modeling and analysis were conducted based on the unit-cell concept with an assumption of a regular square arrangement of the reinforcement within the composite. The mean stress was generally increased with the ceramic volume fraction for composite with strong interface bonding. The micromechanics concept combined with finite element modeling for composite can be used in order to predict the transverse properties of composites with a priori known properties of constituents.

• 소음진동
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• 제10권1호
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• pp.57-63
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• 2000

On the basis of the concept of strain energy-weighted dissipation, an enhanced model for predicting damping in laminates is presented. In this model, the influence of transverse shear on $90^{\circ}$ laminates has been included with those of in-plane stresses on beam. Also, an experimental damping measurement is conducted with changing the length and the thickness of laminated beam specimen for confirmation of the model prediction. The theoretical predictions in $90^{\circ}$laminates were reasonably compared with experimental data. The transverse shear reveals to have an influence on the damping, behavior in $90^{\circ}$ laminates.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권1호
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• pp.157-173
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• 2015

In the present study, the existing equivalent stain method is improved to make up for its weaknesses. The improved inherent strain model is built considering more sophisticated three dimensional constraints which are embodied by six cubic elements attached on three sides of a core cubic element. From a few case studies, it is found that the inherent strain is mainly affected by the changes in restraints induced by changes of temperature-dependent material properties of the restraining elements. On the other hand, the degree of restraints is identified to be little influential to the inherent strain. Thus, the effect of temperature gradients over plate thickness and plate transverse direction normal to welding is reflected in the calculation of the inherent strain chart. The welding deformation can be calculated by an elastic FE analysis using the inherent strain values taken from the inherent strain chart.

• Advances in aircraft and spacecraft science
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• 제2권3호
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• pp.275-302
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• 2015

Theoretical and numerical assessments of approximate evaluations and simplified analyses of piezoelectric structures transverse shear modal effective electromechanical coupling coefficient (EMCC) are presented. Therefore, the latter is first introduced theoretically and its approximate evaluations are reviewed; then, three-dimensional (3D) and simplified two-dimensional (2D) plane-strain (PStrain) and plane-stress (PStress) piezoelectric constitutive behaviors of electroded shear piezoceramic patches are derived and corresponding expected short-circuit (SC) and open-circuit (OC) frequencies and resulting EMCC are discussed; next, using a piezoceramic shear sandwich beam cantilever typical benchmark, a 3D finite element (FE) assessment of different evaluation techniques of the shear modal effective EMCC is conducted, including the equipotential (EP) constraints effect; finally, 2D PStrain and PStress FE modal analyses under SC and OC electric conditions, are conducted and corresponding results (SC/OC frequencies and resulting effective EMCC) are compared to 3D ones. It is found that: (i) physical EP constraints reduce drastically the shear modal effective EMCC; (ii) PStress and PStrain results depend strongly on the filling foam stiffness, rendering inadequate the use of popular equivalent single layer models for the transverse shear-mode sandwich configuration; (iii) in contrary to results of piezoelectric shunted damping and energy harvesting popular single-degree-of-freedom-based models, transverse shear modal effective EMCC values are very small in particular for the first mode which is the common target of these applications.