• Composites Research
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• 제36권6호
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• pp.383-387
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• 2023

탄소섬유 복합재료는 우수한 물성을 바탕으로 산업 전반에 활용되고 있으나 취성이 강하다는 단점이 있다. 연신율이 높은 소재와의 하이브리드화를 통해 강도는 다소 감소되더라도 파괴인성을 향상시킬 수 있다. 이 연구에서는 탄소섬유와 아라미드섬유를 하이브리드한 적층 판재의 물성을 평가하되, 적층 순서를 다르게 하여 이종 재료와의 계면 형성 정도를 조절하였다. 그 결과 25%의 아라미드 섬유 포함 시 순수 탄소섬유 대비 최대 63%의 Izod 충격강도의 향상을 확인할 수 있었으며, 중간 정도의 복잡도를 가진 적층순서 [CF/CAF₂/CF]_s 에서 가장 우수하였다. 그러나 전체적인 복합화 효과는 부정적인 것으로 분석되었다.

• Structural Engineering and Mechanics
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• 제67권6호
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• pp.617-628
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• 2018

This paper deals with the maximization of the critical buckling load of simply supported antisymmetric angle-ply plates resting on Pasternak foundation subjected to compressive loads using teaching learning based optimization method (TLBO). The first order shear deformation theory is used to obtain governing equations of the laminated plate. In the present optimization problem, the objective function is to maximize the buckling load factor and the design variables are the fibre orientation angles in the layers. Computer programming is developed in the MATLAB environment to estimate optimum stacking sequences of laminated plates. A comparison also has been performed between the TLBO, genetic algorithm (GA) and differential evolution algorithm (DE). Some examples are solved to show the applicability and usefulness of the TLBO for maximizing the buckling load of the plate via finding optimum stacking sequences of the plate. Additionally, the influences of different number of layers, plate aspect ratios, foundation parameters and load ratios on the optimal solutions are investigated.

• Steel and Composite Structures
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• 제31권4호
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• pp.387-396
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• 2019

This paper deals with the effect of ply orientation and control gain on tip transverse displacement of functionally graded beam layer for both active constrained layer damping (ACLD) and passive constrained layer damping (PCLD) system. The functionally graded beam is taken as host beam with a bonded viscoelastic layer in ACLD beam system. Piezoelectric fiber reinforced composite (PFRC) laminate is a constraining layer which acts as actuator through the velocity feedback control system. A finite element model has been developed to study actuation of the smart beam system. Fractional order derivative constitutive model is used for the viscoelastic constitutive equation. The control voltage required for ACLD treatment for various symmetric ply stacking sequences is highest in case of longitudinal orientation of fibers of PFRC laminate over other ply stacking sequences. Performance of symmetric and anti-symmetric ply laminates on damping characteristics has been investigated for smart beam system using time and frequency response plots. Symmetric and anti-symmetric ply laminates significantly reduce the amplitude of the vibration over the longitudinal orientation of fibers of PFRC laminate. The analysis reveals that the PFRC laminate can be used effectively for developing very light weight smart structures.

• Structural Engineering and Mechanics
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• 제91권2호
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• pp.135-147
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• 2024

The objective of this study is to analyze, using the finite element method, the durability of damaged and repaired structures under the effect of mechanical loading coupled with environmental conditions (water absorption and/or temperature). The study is based on the hybrid patch repair technique, considering several parameters based on the J integral to observe the behavior of the adhesive in transferring load from a damaged plate to the repair patch. The results clearly show that water absorption and increased temperature cause degradation of the mechanical properties of the adhesive, leading to an increase in its plasticization, which is beneficial for the assembly's strength. However, the degradation of the adhesive's properties due to aging in the repair results in poor load transfer from the damaged area to the patch. The findings of this study allowed the authors to conclude that the [0°]8 sequence consistently offers the best performance, with the lowest J integral values and superior crack resistance. The lowest the J integral for the [0°]8 stacking sequence is typically 3-7% lower than that of the [0/-45/45/90]S and [0/-45/90/45]S sequences at elevated temperatures. At 60℃, the J integral increases by approximately 3-6% compared to 40℃ and 20, depending on the aging duration and stacking sequences.

• 한국정밀공학회지
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• 제22권2호
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• pp.164-171
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• 2005

This study aims to examine an effect of stacking sequence and curvature on the penetration characteristic of a composite laminated shell. For the purpose, we manufactured specimens with different stacking sequences and curvatures, and conducted a penetration test using an air-gun. To examine an influence according to stacking sequence, as flat plate and curvature specimen had more plies, their critical penetration energy was higher, Critical penetration energies of specimen A and C with less interfaces somewhat higher than those of B and D with more interfaces. The reason that with less interfaces, critical penetration energy was higher is pre-impact bending stiffness of composite laminated shell with less interfaces was lower than that of laminated shell with more interfaces, but bending stiffness after impact was higher. And it is because interface, the weakest part of the composite laminated shell, was influenced by transverse impact. As curvature increases, critical penetration energy increases linearly. It is because as curvature increases, resistance to in-plane deformation as well as bending deformation increases, which need higher critical penetration energy. Patterns of cracks caused by penetration of composite laminated shells include interlaminar crack, intralaminar crack, and laminar fracture. A 0$^{\circ}$ply laminar had a matrix crack, a 90$^{\circ}$ply laminar had intralaminar crack and laminar fracture, and interface between 0$^{\circ}$and 90$^{\circ}$laminar had a interlaminar crack. We examined crack length and delamination area through a penetration test. For the specimen A and C with 2 interface, the longest circumferential direction crack length and largest delamination area were observed on the first interface from the impact point. For the specimen B and D with 4 interface, the longest crack length and largest delamination area were observed on the third interface from the impact point.

• 마이크로전자및패키징학회지
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• 제23권3호
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• pp.1-6
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• 2016

IoT 적용을 위해서는 다종 소자를 높은 connectivity 밀도로 집적화시키는 전자패키징 기술이 매우 중요하다. FOWLP 기술은 입출력 밀도가 높고, 소자의 집적화가 우수하고, 디자인 유연성이 우수하여, 최근 개발이 집중되고 있는 기술이다. 웨이퍼나 패널 기반의 FOWLP 기술은 초미세 피치 RDL 공정 기술과 몰딩 기술 개발이 최적화 되어야 할 것이다. 3D stacking 기술 특히 웨이퍼 본딩 후 TSV를 제조하는 방법(via after bonding)은 가격을 낮추면서 connectivity를 높이는데 매우 효과적이라 하겠다. 하지만 저온 웨이퍼 본딩이나 TSV etch stop 공정과 같이 아직 해결해야할 단위 공정들이 있다. Substrate 기술은 두께를 줄이고 가격을 낮추는 공정 개발이 계속 주목되겠지만, 칩과 PCB와의 통합설계(co-design)가 더욱 중요하게 될 것이다.

• 대한기계학회논문집
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• 제12권5호
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• pp.944-951
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• 1988

본 연구에서는 두꺼운 복합적층판에 대한 응력해석을 할 수 있는 통합-세부 변분 모델(globallocal Variational Model)을 이용하여, 이 방법으로 섬유각도와 적 층순서가 다른 여러 유한폭을 가진 복합적층판의 층간응력해석을 수행하여 층간수직 응력의 거동을 살펴 보았다. 그리고 0, 90, 45, -45도 층들로 이루어진 준등방성 (quasiisotropic) 복합적층판에 대한 응력해석 결과로 층간수직응력의 근사해에 의한 결과와 상호 비교하며 근사해의 한계성을 검토 설명하였다. 또한, 층간분리에 큰 영향을 주는 층간수직응력을 고려한 두꺼운 복합적층판에 대한 최적의 적층방법으로 포와송 비에 대하여 대칭인 부적층판을 반복하는 적층방법을 제시하였으며, 통합-세부 변분 모델을 이용한 해로 이 적층방법에 의한 적층판의 층간수직 응력의 거동을 살펴 보았다. 그리고 이 적층방법에 의한 적층판과 다른 적층순서를 가진 적층판의 층간 수직응력을 서로 비교하여, 이 적층방법에 의한 적층판의 층간수직응력의 감소를 조사 하여 그 유용성을 보였다.

• 대한기계학회논문집A
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• 제23권11호
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• pp.1952-1959
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• 1999

The work factor approach, so-called single specimen technique could be used to determine energy release rate from a single test record for unidirectional CLS specimen. In the present study, the work factor approach was extended to determine the mixed-mode fracture toughness of multi-directional graphite/epoxy laminated composites. Multi-directional CLS specimens were used for fracture tests. The stacking sequences used for the lap and the strap were $[90_2/0_2]_s/[0_4/90_4]_s$ and $[0/\pm45/0]_s/[0_2/\pm45_2/0_2]_2$, respectively. For both cases, the fracture toughness determined from the work factor approach was compared with that determined from the compliance method. It was found that both methods produced fracture toughness within a maximum 15% difference for each stacking sequence. The fractography analysis also showed that the fiber bridging occurred for$[0/\pm45/0]_s/[0_2/\pm45_2/0_2]_2$ case while it did not occur for $[90_2/0_2]_s/[0_4/90_4]_s$ case.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.173-177
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• 2004

In this study, the effect of laminate thickness on the compressive behaviour of composite materials was investigated through systematic experimental work using the stacking sequences, [04]ns, [45/0/-45/90]ns and [45n/0n/-45n/90n]s (n = 2 to 8). The stacking sequence effects on failure strength of multidirectional laminates were examined. For this purpose, two different scaling techniques were used; (1) ply-level technique [45n/0n/-45n/90n]s and (2) sub laminate level technique [45/0/-45/90]ns. An apparent thickness effect existed in the lay-up with blocked plies, i.e. unidirectional specimens $([0_4]ns)$ and ply-level scaled multidirectional specimens ([45n/0n/-45n/90n]s). From the investigation of the stacking sequence effect, the strength values obtained from the sub laminate level scaled specimens were slightly higher than those obtained from the ply level scaled specimens. The measured failure strengths were compared with the predicted values

• 대한기계학회논문집
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• 제13권4호
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• pp.643-652
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• 1989

본 연구에서는 저자들에 의해 개발된 보와 판의 동적 유한 요소법으로 보형상을 지닌 적층 복합재의 형상비(길이/폭)와 적층 형태의 변화에 따른 충격 해석시 어느 이론의 결과가 더욱 적합한지에 대한 타당성 여부를 검토하고자 한다.