• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.3
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• pp.21-28
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• 1989

The optimun laminated composition of the stiffened composite plates is studied from the view point of buckling strength. The finite element method is applied to the buckling analysis of the composite plates taking into account the effect of shear deformation through the plate thickness. The stiffened plate model is discretized using plate thickness and symmetrically stacked. Parametric study is carried out for the selection of the optimum laminate structure; optimum fiber angle sequence through the thickness. Laminate structure of $[-45^{\circ}/45^{\circ}/90^{\circ}/0^{\circ}]$, is found to give the best buckling strength. For the case of that layer number is more than eight, best result is obtained when layers of the same fiber angle are put together, leaving the laminate has the same fiber angle sequence as a whole.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.3
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• pp.191-196
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• 2022

In this study, the anisotropic mechanical property of fused deposition modeling three-dimensional (3D) printing based on lamination direction was verified by a tensile test. Moreover, the property was applied to solid isotropic materials with penalization-based topology optimization. The case of the lower control arm, one of the automotive suspension components, was considered as a benchmark problem. The optimal topological results varied depending on the external load and anisotropic property. Based on these results, two test specimens were fabricated by varying the lamination direction of 3D printing; a tensile test utilizing 3D non-contact strain gauge was also conducted. The measured strain was compared with that obtained by computer-aided engineering response analysis. Quantitatively, the measurement and analysis results are found to have good agreement. The effectiveness of topology optimization considering the lamination direction of 3D printing was confirmed by the experimental result.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.729-732
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• 2010

본 논문에서는 이산 변수 최적화에 적합한 유전 알고리듬을 이용하여 복합재 적층 패치의 최적강도설계를 수행하였다. 기저판(substrate)와 접착제(adhesive), 그리고 복합재 적층 패치로 이루어진 구조물에서 패치의 강도를 효율적으로 구하기 위해서 응력 함수 기반의 해석적 방법을 도입하였다. 면외 방향의 응력 함수를 가정하여 가상 공액일의 법칙(complementary virtual work principle)에 적용하였으며, 복합재 패치의 자유 경계조건으로부터 면내 방향의 응력함수를 결정하였다. 응력 함수를 통하여 구한 층간 응력 값은 자유 경계 효과를 잘 나타내었고, 이를 이용하여 패치의 강도 해석을 수행하였다. 강도 해석 시, 복합재 패치의 파괴 기준은 면내 응력들에 대해서는 최대 응력 척도를 사용하였으며, 층간 응력들에 대해서는 quadratic delamination 척도를 사용하였다. 유전 알고리듬을 이용한 최적강도설계 과정에서는 임의의 염색체가 주어진 적층 구속 조건을 만족할 수 있게 수정(repairing)하는 과정을 도입하였다. 또한 다수의 전역해(global optima)를 효과적으로 찾기 위해서 multiple elitism 기법을 도입하였다. 응력 함수 기반의 강도 해석방법과 유전 알고리듬과의 연계를 통한 복합재 적층 패치의 강도최적설계 기법은 패치 구조물의 해석 및 설계에 있어서 효율적인 도구로서 사용할 수 있을 것이라 사료된다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.2
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• pp.107-116
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• 2001

복합재 적층판은 중량에 비해 높은 강성과 강도가 요구되는 공학의 다양한 분야에서 매우 유용하다. 보강섬유 복합재의 공학적 활용이 활발해지고, 중량의 감소화가 설계의 중요한 목적이 됨으로써, 근래 복합재 구조물들의 최적화 설계의 중요성이 대두되고 있다. 그러나 복합재 적층 구조물 재료의 비등방성에 의해 해석과 설계가 매우 어렵다. 본 연구에서는 수치적 최적화 방법과 유한요소법을 이용하여 보강섬유 복합재의 최적설계를 하였다. 복합재 적층판으로 이루어진 개단면 보에 있어서 보강섬유의 다양한 적층방향에 대한 거동의 영향을 규명하였다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.288-293
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• 2023

To optimize the process parameters of laser powder bed fusion process to fabricate the high density STS316L alloy, the effect of laser power, scanning speed and hatching distance on the relative density was studied. Tensile properties of additively manufactured STS316L alloy using optimized parameters was also evaluated according to the build direction. As a result of additive manufacturing process under the energy density of 55.6 J/mm³, 83.3 J/mm³ and 111.1 J/mm³, high density STS316L specimens was suitably fabricated when the energy density, power and scan speed were 83.3 J/mm³, 225 W and 1000 mm/s, respectively. The yield strength, ultimate tensile strength, and elongation of STS316L specimens in direction perpendicular to the build direction, show the most competitive values. Anisotropic shape of the pores and the lack of fusion defects probably caused strain localization which result in deterioration of tensile properties.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.2
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• pp.189-196
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• 2009

This paper presents the subparametric finite element model formulated by partial-linear layerwise theory for the analysis of laminate composites. The proposed model is based on refined approximations of two dimensional plane for orthotropic thick laminate plate as well as thin case. Three dimensional problem can be reduced to two dimensional case by assuming piecewise linear variation of in-plane displacement and a constant value of out-of-plane displacement across the thickness. The integrals of Legendre polynomials are chosen to define displacement fields and Gauss-Lobatto numerical integration is implemented in order to directly obtain maximum values occurred at the nodal points of each layer without other extrapolation techniques. The validity and characteristics of the proposed model have been tested by using orthotropic multilayered plate problem as compared to the values available in the published references. In this study, the convergence test has been carried out to determine the optimal layer model in terms of central deflection and stresses. Also, the distribution of displacements and stresses across the thickness has been investigated as the number of layer is increased.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.1
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• pp.29-34
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• 2012

Even though the longitudinally stiffened laminated composite plates with closed section ribs should be an effective system for axially compressed members, the existing researches on the applications of closed-section ribs, especially for the laminated composite plates, are not sufficient. This study is aimed to examine the influence of the sectional stiffness of U-shaped ribs on the buckling modes and strengths of laminated composite plates. Applying the orthotropic plates with eight layers of the layup $[(0^{\circ})_4]_s$ and $[(0^{\circ}/90^{\circ})_2]_s$, 3-dimensional finite element models for the U-rib stiffened plates were setup by using ABAQUS and then a series of eigenvalue analyses were conducted. From the parametric studies, the minimum required ply thicknesses as well as the buckling strengths were presented for the analysis models. The buckling strengths were compared with the theoretical critical stress equation for simply supported plates based on the Classical laminated plate theory. This study will contribute to the future study for evaluating the minimum required stiffness and optimum design of U-rib stiffened plates.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.65-74
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• 1993

The buckling load of a blade stiffened laminated composite plate having midplane symmetry is maximized for a given total weight. The thicknesses of the layers and the width and height of the stiffener are taken as the design variables. Buckling analysis is carried out using a finite element method. The optimization problem is solved using an IMSL subroutine. Due to the highly nonlinear nature of the optimality equations, several local optimum solutions are found. Various combinations of fiber orientation for the laminate layers and the blade stiffener are investigated to examine their relative efficiency. Out of several cases examined, the best design was produced from the combination of ($0^{\circ}Beam/0^{\circ}/90^{\circ}$)s.

• Composites Research
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• v.33 no.1
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• pp.13-18
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• 2020

Recently, the fire rescue truck in problem proceed research it for the fast works action and for pass the small road. So we were research for weight reduction. In this study, the (NO. 5) fifth boom of the fire rescue truck have 288 mm(W) × 299 mm(D) × 3,691 mm(L) with a maximum load of 876 kg and the thickness of 3 mm of the Steel Boom. This changing of Steel (STRENX960) to CFRP was weave Carbon Fiber NCF (±45°, 2axis) and then it make the NCF Prepreg. This process was designed based on structural analysis, the effects of NCF Prepreg (±45°) on torsion were identified, and the optimal design was made with Stacking Pattern (b). Stack patterns were optimized for levels equal or higher than existing Steel Boom and CFRP Boom stacked in the UD direction, and finally, the lightening effect on weight of approximately 49.6% of the steel was identified.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.944-951
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• 1988

Global-Local Laminate Variational Model is utilized to investigate the characteristics of interlaminar stresses in thick composite laminates under uniform axial extension. Various laminates with different fiber orientation and stacking sequences are analyzed to observe the behavior of interlaminar normal stresses. From this result, the interlaminar normal stress distribution along the laminate interfaces is examined and discussed with an existing approximation model. The repeated stacking of Poisson's ratio symmetric sublaminates is found to be the best stacking method of thick composite laminates to reduce the interlaminar normal stresses for the prevention of the free-edge delamination.