• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 춘계학술대회 논문집
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• pp.132-137
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• 2007

This paper explains compressive behaviors of sandwich composite laminates with adhesively bonded patches. The sandwich composite laminate is used for a train carbody structure and is of an aluminum honeycomb core and CF1263 woven fabric carbon/epoxy faces. The sandwich composite laminates were damaged by low velocity impact. The damaged sandwich composite laminate was repaired using scarf repair method. Then, the strength restoration of it was assessed by compressive test. From the test, it could be known that the compressive strength was restored up to 91% of undamaged one.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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• pp.268-271
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• 1999

Fatigue life Prediction is investigated analytically based on the fatigue modulus concept. Fatigue modulus degradation rate at any fatigue cycle was assumed as a power function of number of fatigue cycles. New stress function describing the relation of initial fatigue modulus and elastic modulus was used to account for material non-linearity at the first cycle. It was assumed that fatigue modulus at failure is proportional to applied stress level. A new fatigue life prediction equation as a function of applied stress is proposed. The prediction was verified experimentally using cross-ply carbon/epoxy laminate (CFRP) tube.

• Composites Research
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• 제12권6호
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• pp.1-7
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• 1999

본 논문은 탄소/에폭시 적층판의 온도변화에 대한 열팽창계수 변화를 예측하고 실험적으로 검증한 것으로 재료의 주축 방향에 대한 기계적 탄성 특성과 열팽창계수를 상온에서 경화온도 범위까지 측정하였으며 온도 함수로 특성화 하였다. 온도 함수로 특성화된 물성을 고전 적층판 이론에 적용함으로써 온도 변화에 대해 일반 적층각 적층판 복합재료의 열팽창계수를 예측할 수 있는 해석적 모델을 제시하였다. 이를 증명하기 위해서 일반 적층각 적층판의 열팽창계수를 측정하였으며 이를 해석적 모델로 계산된 예측치와 비교하였다. 실험적 검증 결과 온도 변화에 대한 일반 적층판의 열팽창계수의 변화가 제시된 해석적인 계산 방법을 사용함으로써 적절하게 예측될수 있음을 볼수 있다.

• 대한기계학회논문집A
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• 제25권10호
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• pp.1514-1519
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• 2001

This paper is concerned with design, manufacturing and performance test of LIPCA ( Lightweight Piezo- composite Curved Actuator) using a top carbon fiber composite layer with near -zero CTE(coefficient of thermal expansion), a middle PZT ceramic wafer and a bottom glass/epoxy layer with high CTE. The main point of this design is to replace the heavy metal layers of THUNDER by thigh tweight fiber reinforced plastic layers without losing capabilities to generate high force and large displacement. It is possible to save weight up to about 30% if we replace the metallic backing material by the light fiber composite layer. We can also have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use epoxy resin prepreg system. Glass/epoxy prepregs, a ceramic wafer with electrode surfaces, and a graphite/epoxy prepreg were simply stacked and cured at an elevated temperature (177 $^{circ}C$ after following an autoclave bagging process. It was found that the manufactured composite laminate device had a sufficient curvature after detached from a flat mold. The analysis method of the cure curvature of LIPCA using the classical lamination theory is presented. The predicted curvatures are fairly in agreement with the experimental ones. In order to investigate the merits of LIPCA, a performance test of both LIPCA and THUNDE$^{TM}$ were conducted under the same boundary conditions. From the experimental actuation tests, it was observed that the developed actuator could generate larger actuation displacement than THUNDERT$^{TM}$.

• Advanced Composite Materials
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• 제17권1호
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• pp.57-73
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• 2008

The present paper focuses on experimental verification of the ply-by-ply basis inelastic analysis of multidirectional laminates. First of all, rate dependence of the tensile behavior of balanced symmetric cross-ply T800H/epoxy laminates with a $[0/90]_{3S}$ lay-up under off-axis loading conditions at $100^{\circ}C$ is examined. Uniaxial tension tests are performed on plain coupon specimens with various fiber orientations $[{\theta}/(90-{\theta})]_{3S}$ ($\theta$ = 0, 5, 15, 45 and $90^{\circ}C$) at two different strain rates (1.0 and 0.01%/min). The off-axis stress.strain curves exhibit marked nonlinearity for all the off-axis fiber orientations except for the on-axis fiber orientations $\theta$ = 0 and $90^{\circ}$, regardless of the strain rates. Strain rate has significant influences not only on the off-axis flow stress in the regime of nonlinear response but also on the apparent off-axis elastic modulus in the regime of initial linear response. A macromechanical constitutive model based on a ply viscoplasticity model and the classical laminated plate theory is applied to predictions of the rate-dependent off-axis nonlinear behavior of the cross-ply CFRP laminate. The material constants involved by the ply viscoplasticity model are identified on the basis of the experimental results on the unidirectional laminate of the same carbon/epoxy system. It is demonstrated that good agreements between the predicted and observed results are obtained by taking account of the fiber rotation induced by deformation as well as the rate dependence of the initial Young's moduli.

• Steel and Composite Structures
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• 제18권3호
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• pp.583-601
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• 2015

In the present study, the combined effects of thermal and mechanical loadings on the interlaminar shear stresses of both moderately thin and thick composite laminated beams are numerically analyzed. The finite element modelling of laminated composite beams and analysis of interlaminar stresses are performed using the commercially available software package MSC NASTRAN/PATRAN. The validity of the finite element analysis (FEA) is demonstrated by comparing the experimental test results obtained due to mechanical loadings under the influence of thermal environment with those derived using the present FEA. Various parametric studies are also performed to investigate the effect of thermal loading on interlaminar stresses generated in symmetric, anti-symmetric, asymmetric, unidirectional, cross-ply, and balanced composite laminated beams of different stacking sequences with identical mechanical loadings and various boundary conditions. It is shown that the elevated thermal environment lead to higher interlaminar shear stresses varying with the stacking sequence, length to thickness ratio, ply orientations under identical mechanical loading and boundary conditions of the composite laminated beams. It is realized that the magnitude of the interlaminar stresses along xz plane is always much higher than those of along yz plane irrespective of the ply-orientation, length to thickness ratios and boundary conditions of the composite laminated beams. It is also observed that the effect of thermal environment on the interlaminar shear stresses in carbon-epoxy fiber reinforced composite laminated beams are increasing in the order of symmetric cross-ply laminate, unidirectional laminate, asymmetric cross-ply laminate and anti-symmetric laminate. The interlaminar shear stresses are higher in thinner composite laminated beams compared to that in thicker composite laminated beams under all environmental temperatures irrespective of the laminate stacking sequence, ply-orientation and boundary conditions.

• 대한기계학회논문집A
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• 제41권10호
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• pp.959-965
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• 2017

최근 선진항공사에서는 항공기 복합재 구조의 변형률을 평가할 때 적층판 파손이론을 사용한다. 적층판 파손이론은 복합재 구조평가에 적층판의 파손변형률을 사용한다. 본 논문은 적층판 인장파손특성의 시험적 평가 절차를 보여준다. 시험적 평가는 회귀분석법(regression analysis method)을 사용하였다 회귀분석은 적층판의 파손변형률을 응답변수로 하고 적층판 내 $0^{\circ}$, ${\pm}45^{\circ}$층의 비율을 회귀변수로 하는 방법이다. 본 논문에 사용된 복합재료는 $177^{\circ}C(350^{\circ}F)$에서 경화되는 Carbon/Epoxy UD Tape 프리프레그이다. 시편은 $0^{\circ}$, $+45^{\circ}$, $-45^{\circ}$ 및 $90^{\circ}$층으로 적층된 14 종류의 노치없는 적층판으로 총 149개 시편으로 구성하였다. 시험방법은 ASTM-D-3039 규정을 사용하였다.

• 한국정밀공학회지
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• 제27권2호
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• pp.102-108
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• 2010

Recently, carbon fiber reinforced plastic(CFRP) composite materials have been widely used in various fields of engineering because of its advanced properties. Also, CFRP composite materials offer new design flexibilities, corrosion and wear resistance, low thermal conductivity and increased fatigue life. However CFRP composite materials are susceptible to impact damage due to their lack of through-thickness reinforcement and it causes large drops in the load-carrying capacity of a structure. Therefore, the impact damage behavior and subsequently load-carrying capacity of impacted composite materials deserve careful investigation. In this study, the residual strength and impact characteristics of plain-woven CFRP composites with impact damage are investigated under axial tensile test. By using obtained residual strength and Tan-Cheng failure criterion, residual strength of CFRP laminate with arbitrary fiber angle were evaluated.

• International Journal of Aeronautical and Space Sciences
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• 제16권2호
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• pp.190-205
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• 2015

In this paper, the impact damage behavior of USN-150B carbon/epoxy composite laminates subjected to high velocity impact was studied experimentally and numerically. Square composite laminates stacked with $[45/0/-45/90]_{ns}$ quasi-symmetric and $[0/90]_{ns}$ cross-ply stacking sequences and a conical shape projectile with steel core, copper skin and lead filler were considered. First high-velocity impact tests were conducted under various test conditions. Three tests were repeated under the same impact condition. Projectile velocity before and after penetration were measured by infrared ray sensors and magnetic sensors. High-speed camera shots and C-Scan images were also taken to measure the projectile velocities and to obtain the information on the damage shapes of the projectile and the laminate specimens. Next, the numerical simulation was performed using explicit finite element code LS-DYNA. Both the projectile and the composite laminate were modeled using three-dimensional solid elements. Residual velocity history of the impact projectile and the failure shape and extents of the laminates were predicted and systematically examined. The results of this study can provide the understanding on the penetration process of laminated composites during ballistic impact, as well as the damage amount and modes. These were thought to be utilized to predict the decrease of mechanical properties and also to help mitigate impact damage of composite structures.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 추계학술대회 논문집
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• pp.111-115
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• 2001

The stress and torque transmission capability of the tubular, hexagonal and elliptic single lap joints were analyzed by the finite element method (ANSYS 4.4A) and compared to those with the experimental results. The adherends of the joints were composed of the carbon fiber epoxy composite shafts and the steel shafts. In calculating the torque capability, the linear laminate (smeared) properties of the composite and the nonlinear shear properties of the adhesive were used. The experiments revealed that the torque capability calculation performed by this method gave accurate results.