• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.135-138
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• 2004

Because the compressive properties such as compressive stiffness and compressive maximum strength of the fabric composite materials are essential to analyse the drape behaviour and estimate the quality of the final products, compressive tests of fabric composites with different stacking sequences were performed. Appropriate shape and dimensions for the compressive test specimens were prepared and several specimens with different conditions were tested and compared with each other.

• 한국석유지질학회:학술대회논문집
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• autumn
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• pp.14-30
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• 2000

Hierarchically controlled sequence stratigraphic analysis shows that the Lower Ordovician mixed carbonate-siliciclastic Mungok Formation, Korea consists of three depositional sequences: T1, T2, and T3. Sequence boundaries are generally marked by abrupt transition from coarse-grained shallow-water carbonates to fine-grained deeper-water carbonates mixed with fine-grained siliciclastics, and show indication of subaerial exposure such as karstification. Within this sequence stratigraphic framework, facies characteristics indicate that the Mungok sequences were mostly deposited in subtidal ramp environments. High-frequency cycles consist of upward-shallowing facies successions. Cycles of shallow-water and basinal deposits are not represented well, probably due to cycle amalgamation. Cycle stacking patterns do not show a consistent thickness change that reflects a large-scale sea-level change due to unfilled accommodation space. The Mungok sequences show that many factors including relative sea-level change and topography are involved in controlling sequence development on carbonate ramps. The depositional setting evolved from the high-energy ramps in the sequences T1 and T2 into the low-energy ramp in the sequence T3. Topography is interpreted to have been responsible for the different energy regimes of the carbonate ramps in the Mungok sequences. The high ramp gradient in the sequences T1 and T2 seems to be caused by space-time-dissociated differential sedimentation resulting in spatially narrow distribution of sediment filling, which in turn may be related to high rate of relative sea-level change. In contrast, low ramp gradient was maintained in the sequence T3 during slow changes of relative sea level resulting in broad distribution of sediment filling.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.747-769
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• 2020

This paper provides a semi-analytical approach to investigate the variations of 3D displacement components, electric potential, stresses, electric displacements and transverse vibration frequencies in laminated piezoelectric composite plates based on the scaled boundary finite element method (SBFEM) and the precise integration algorithm (PIA). The proposed approach can analyze the static and dynamic responses of multilayered piezoelectric plates with any number of laminae, various geometrical shapes, boundary conditions, thickness-to-length ratios and stacking sequences. Only a longitudinal surface of the plate is discretized into 2D elements, which helps to improve the computational efficiency. Comparing with plate theories and other numerical methods, only three displacement components and the electric potential are set as the basic unknown variables and can be represented analytically through the transverse direction. The whole derivation is built upon the three dimensional key equations of elasticity for the piezoelectric materials and no assumptions on the plate kinematics have been taken. By virtue of the equilibrium equations, the constitutive relations and the introduced set of scaled boundary coordinates, three-dimensional governing partial differential equations are converted into the second order ordinary differential matrix equation. Furthermore, aided by the introduced internal nodal force, a first order ordinary differential equation is obtained with its general solution in the form of a matrix exponent. To further improve the accuracy of the matrix exponent in the SBFEM, the PIA is employed to make sure any desired accuracy of the mechanical and electric variables. By virtue of the kinetic energy technique, the global mass matrix of the composite plates constituted by piezoelectric laminae is constructed for the first time based on the SBFEM. Finally, comparisons with the exact solutions and available results are made to confirm the accuracy and effectiveness of the developed methodology. What's more, the effect of boundary conditions, thickness-to-length ratios and stacking sequences of laminae on the distributions of natural frequencies, mechanical and electric fields in laminated piezoelectric composite plates is evaluated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.3
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• pp.105-108
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• 2008

Four different thin films were made by depositing PZ and PT in different stacking sequences. PZ and PT phases are preferably co-existed in sample A and C that are annealing after each coatings. The sample B and D, on the other hands, have tendency toward the PZT phase after co-firing the sample. The sample B that started from PT stacking first was more stable PZT phase than that of PZ first sample D.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.141-145
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• 2005

Since the electromagnetic properties of fiber reinforced polymeric laminate composite can be tailored effectively by adjusting its composition and regulating the stacking sequence, it is plausible material for fabricating the radar absorbing structures (RAS) of desired performance. In order to design the effective electromagnetic wave (EM) absorber with the fiber reinforced polymeric laminate composite, its electromagnetic characteristics should be available and could be regulated easily in the target frequency bands. In this study, dielectric characteristics of the E-glass/epoxy laminate composites were measured by the free space method in the X-band frequency range ($8.2\;{\sim}\;12.4\;GHz$). In order to describe the dielectric behavior of laminate composites of arbitrary stacking sequences, the equivalent circuit model and the laminating equations for estimating dielectric properties were proposed, and experimentally verified. From the comparison of the predicted and measured data, the proposed method predicted well the experimentally measured data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2306-2314
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• 1992

Using the Lagrangian equation, nonlinear vibration analysis of laminated hybrid composite plates is carried out. The effects of stacking sequences, aspect ratios, number of modes, number of layers and various elastic properties on nonlinear vibration are investigated. The presence of bending-extension coupling in antisymmetric plates yields a second power term in addition to a cubic nonlinear term in governing differential equation of motion. In the other symmetric case, this second term vanishes. The fundamental frequency of analytic results are compared with that of ABAQUS FEM analysis. For nonlinear vibration of antisymmetric unimaterial plate, the result of reference is presented for comparison with this result.

• Composites Research
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• v.33 no.3
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• pp.133-139
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• 2020

In this research, the vibration characteristics of composite quadcopter are analyzed, and avoidance design and analysis are performed to avoid resonance. The full platform of a commercial quadcopter with composite rotor arm is analyzed to see the vibration characteristics using FEM program. The manufactured stacking sequences of rotor arm is used for analysis, and the natural frequencies are compared with experimental results and simple analytic model results. It is also confirmed that the natural frequency of the particular mode is included within the operation range of the motor. The resonance avoidance design is carried out by selecting three variables from the existing model: stacking sequence, rotor-arm pipe length, and pipe thickness.

• Journal of Ocean Engineering and Technology
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• v.27 no.2
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• pp.8-12
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• 2013

Four kinds of silicon nitride composites with tri-laminate structure were prepared by stacking tapes with aligned ${\beta}-Si_3N_4$ whisker seeds. The composites were fabricated using a modified tape casting method for enhanced alignment of the whisker seeds. The relative densities of all four samples reached 99% at room temperature. The three-point flexural strengths of the samples according to the stacking sequences were measured at both room temperature and 1723 K. The high temperature strength of sample WWW was $457{\pm}14$ MPa. The fracture of sample WWW occurred mainly along the grain boundary. The room temperature strengths of samples OOO, OWO, WOW, and WWW were $430{\pm}32$ MPa, $470{\pm}19$ MPa, $700{\pm}14$MPa, and $940{\pm}14$ MPa, respectively.

• Steel and Composite Structures
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• v.29 no.6
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• pp.749-758
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• 2018

This article derived a hybrid coupling technique using the higher-order displacement polynomial and three soft computing techniques (teaching learning-based optimization, particle swarm optimization, and artificial bee colony) to predict the optimal stacking sequence of the layered structure and the corresponding frequency values. The higher-order displacement kinematics is adopted for the mathematical model derivation considering the necessary stress and stain continuity and the elimination of shear correction factor. A nine noded isoparametric Lagrangian element (eighty-one degrees of freedom at each node) is engaged for the discretisation and the desired model equation derived via the classical Hamilton's principle. Subsequently, three soft computing techniques are employed to predict the maximum natural frequency values corresponding to their optimum layer sequences via a suitable home-made computer code. The finite element convergence rate including the optimal solution stability is established through the iterative solutions. Further, the predicted optimal stacking sequence including the accuracy of the frequency values are verified with adequate comparison studies. Lastly, the derived hybrid models are explored further to by solving different numerical examples for the combined structural parameters (length to width ratio, length to thickness ratio and orthotropicity on frequency and layer-sequence) and the implicit behavior discuss in details.

• Composites Research
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• v.15 no.5
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• pp.14-18
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• 2002

In the present study, we investigated the effects or hydrostatic pressure and stacking sequence on the elastic work factor to determine compressive fracture toughness of graphite/epoxy laminated composites in the hydrostatic pressure environment. The stacking sequences used were unidirectional. $\textrm{[}0^{\circ}\textrm{]}_{88}$ and multi-directional, $\textrm{[}0^{\circ}/\pm/45^{\circ}/90^{\circ}\textrm{]}_{11s}$. The hydrostatic pressures applied for a $\textrm{[}0^{\circ}\textrm{]}_{88}$ case were 0.1 MPa, 70MPa, 140MPa. and 200MPa. The hydrostatic pressures applied for a $\textrm{[}0^{\circ}/\pm/45^{\circ}/90^{\circ}\textrm{]}_{11s}$ case were 0.1MPa, 100MPa, 200MPa, and 300MPa. It was found that the elastic work factor was not affected by the hydrostatic pressure and the stacking sequence. Also, it was found that the elastic work factor decreased in a linear fashion with delamination length.