• International Journal of Aeronautical and Space Sciences
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• 제14권4호
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• pp.350-355
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• 2013

Electrical resistance change measurements were performed, to detect fatigue damage of a quasi-isotropic CFRP and cross-ply CFRP laminates. A four-probe method was used to measure the exact electrical resistance change. A three-probe method was used to measure the electrical contact resistance change, during long cyclic loading. The specimen side surface was observed using a video-microscope to detect damage. The measured electrical resistance changes were compared with the observed damage. The results of this study show that the electrical resistance increase of the quasi-isotropic laminate was caused by a delamination crack between ${\pm}45^{\circ}$ plies. Matrix cracking caused a small electrical resistance increase of the cross-ply laminate, but the decreased electrical resistance caused by the shear-plastic deformation impedes matrix-cracking detection.

• Steel and Composite Structures
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• 제12권4호
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• pp.303-324
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• 2012

This paper presents the mode-shape analysis of the cross-ply laminated composite cylindrical shallow shells. First, the kinematic relations of strains and deformation are given. Then, using Hamilton's principle, governing differential equations are developed for a general curved shell. Finally, the stress-strain relation for the laminated, cross-ply composite shells are obtained. By using some simplifications and assuming Fourier series as a displacement field, the governed differential equations are solved by the matrix algebra for shallow shells. Employing the computer algebra system called MATHEMATICA; a computer program has been prepared for the solution. The results obtained by this solution are compared with the results obtained by (ANSYS and SAP2000) programs, in order to verify the accuracy and reliability of the solution presented.

• Structural Engineering and Mechanics
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• 제35권4호
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• pp.493-510
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• 2010

This paper presents effects of anisotropy and curvature on free vibration characteristics of cross-ply laminated composite cylindrical shallow shells. Shallow shells have been considered for different lamination thickness, radius of curvature and elasticity ratio. First, kinematic relations of strains and deformation have been showed. Then, using Hamilton's principle, governing differential equations have been obtained for a general curved shell. In the next step, stress-strain relation for laminated, cross-ply composite shells has been given. By using some simplifications and assuming Fourier series as a displacement field, differential equations are solved by matrix algebra for shallow shells. The results obtained by this solution have been given tables and graphs. The comparisons made with the literature and finite element program (ANSYS).

• Advances in nano research
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• 제7권5호
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• pp.337-349
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• 2019

The size-dependent vibration analysis of a cross-/angle-ply laminated composite plate when embedded on the Pasternak elastic foundation and exposed to an in-plane magnetic field are investigated by adopting an analytical eigenvalue approach. The formulation, which is based on refined-hyperbolic-shear-deformation-plate theory in conjunction with the Eringen Nonlocal Differential Model (ENDM), is tested against considering problems for which numerical/analytical solutions available in the literature. The findings of this study demonstrated the role of magnetic field, size effect, elastic foundation coefficients, geometry, moduli ratio, lay-up numbers and fiber orientations on the nonlocal frequency of cross-/angle-ply laminated composite plates.

• 대한기계학회논문집A
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• 제22권3호
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• pp.579-587
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• 1998

In this study, fatigue behavior of the optical fiber sensor embedded in composite laminate was investigated. Static tensile and fatigue tests were performed for three types of laminated composite specimens with embedded optical fiber sensor in the neutral plane ; [0/sub 6//OF/0/sub 6/]/sub T/, [0/sub 2//90/sub 4//OF/90/sub 4//0/sub 2/]/sub T/ and [0/sub 3//90/sub 3//OF/90/sub 3//0/sub 3/]/sub T/. The fracture of the embedded optical fiber sensor was detected by the intensity drop off of laser signal transmitted through the optical fiber sensors embedded within laminated composite specimen. The maximum fatigue stress applied to laminated specimen was compared with the average tensile stress at which the fracture of the embedded optical fiber within the laminate occurred under static tensile loading. From the experiments, firstly it is observed that the decrease in the life of optical fiber sensors embedded within unidirectional-ply laminate by the fatigue loading is relatively small compared to that of cross-ply laminate. Secondly, the optical fiber embedded in unidirectional-ply laminate is fractured by the fatigue damage due to the growth of internal defects of optical fiber, however the optical fiber embedded in cross-ply laminate is fractured by the growth of transverse matrix crack.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.38-42
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• 2002

An apparatus was developed to repetitively apply a $-196^{\circ}C$ thermal load to coupon-sized mechanical test specimens. Using this device, IM7/5250-4 (carbon / bismaleimide) cross-ply and quasi-isotropic laminates were submerged in liquid nitrogen ($LN_2$) 400 times. Ply-by-ply micro-crack density, laminate modulus, and laminate strength were measured as a function of thermal cycles. Quasi-isotropic samples of IM7/977-3 (carbon / epoxy) composite were also manually cycled between liquid nitrogen and an oven set at $120^{\circ}C$ for 130 cycles to determine whether including elevated temperature in the thermal cycle significantly altered the degree or location of micro-cracking. In response to thermal cycling, both materials micro-cracked extensively in the surface plies fellowed by sparse cracking of the inner plies. The tensile modulus of the IM7/5250-4 specimens was unaffected by thermal cycling, but the tensile strength of two of the lay-ups decreased by as much as 8.5%.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.151-155
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• 2003

An apparatus was developed to repetitively apply a -196 $^{\circ}C$ thermal load to coupon-sized mechanical test specimens. Using this device, IM7/5250-4 (carbon / bismaleimide) cross-ply and quasi-isotropic laminates were submerged in liquid nitrogen (L$N_2$) 400 times. Ply-by-Ply micro-crack density, laminate modulus, and laminate strength were measured as a function of thermal cycles. Quasi-isotropic samples of IM7/977-3 (carbon / epoxy) composite were also manually cycled between liquid nitrogen and an oven set at 120 $^{\circ}C$ for 130 cycles to determine whether including elevated temperature in the thermal cycle significantly altered the degree or location of micro-cracking. In response to thermal cycling, both materials micro-cracked extensively in the surface plies followed by sparse cracking of the inner plies. The tensile modulus of the IM7/5250-4 specimens was unaffected by thermal cycling, but the tensile strength of two of the lay-ups decreased by as much as 8.5 %.

• Geomechanics and Engineering
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• 제18권5호
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• pp.555-566
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• 2019

The purpose of this paper is to investigate the thermal effects on the behaviour reinforced-concrete beams strengthened by bonded angle-ply laminated composites laminates plate $[{\pm}{\theta}n/90m]_S$. Effects of number of $90^{\circ}$ layers and number of ${\pm}{\theta}$ layers on the distributions of interfacial stress in concrete beams reinforced with composite plates have also been studied. The present results represent a simple theoretical model to estimate shear and normal stresses. The effects the temperature, mechanical properties of the fibre orientation angle of the outer layers, the number of cross-ply layers, plate length of the strengthened beam region and adhesive layer thickness on the interfacial shear and normal stresses are investigated and discussed.

• 대한기계학회논문집
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• 제15권6호
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• pp.2002-2014
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• 1991

본 연구에서는 모재균열의 열림변위로 인한 변형을 고려하여, 모재균열 주위 의 응력분포를 구하기 위한 2차원 해석방법을 제안한다. 제안된 방법은 두께방향 다 항식 형태로 가정된 변위성분으로부터 모재균열 주쥐의 변위, 응력분포를 구한다. 본 방법은 적층판의 프아송비(Poisson's ratio) 효과와 열잔류응력(thermal residual stress)의 영향을 고려하였으며, 계면층(interface layer) 개념을 사용하여 특성손상 상태 이후에 발생하는 층간분리를 평가하기 위한 기초자료인 층간수직응력과 층간전단 응력을 결정하였다. 제안된 방법의 타당성을 검증하기 위하여, 유한요소해석(finite element analysis)을 수행하여 제안된 방법의 응력분포 결과를 유한요소해석 결과와 비교하여 보았다.

• Composites Research
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• 제17권5호
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• pp.15-24
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• 2004

유리 섬유 강화 플라스틱 직교적층판의 내부층과 표피층의 길이방향 변형률을 삽입된 절대변형 외부 페브리 페로 간섭 센서를 이용하여 측정하였다. 투과식 광학현미경을 이용하여 삽입된 A-EFPI 센서 주위의 파손거동을 관찰하였다. 시험편 표면부의 변형률 측정을 위해 포일 형식의 스트레인 게이지를 시험편 아래 위 표면부에 부착하였다. 또한 삽입된 A-EFPI 센서로 측정한 내부층과 표피층의 길이방향 변형률 값은 스트레인 게이지로 측정한 시험편 표면의 변형률 값 보다 다소 크게 나타났다. 균일 응력 모델을 기초로 한 3차원 유한요소해석을 통해 실험 결과의 타당성을 확인하였으며 내부층의 큰 변형률은 많은 횡단형 균열의 발생을 야기시켰는데 이로 인해 내부층에 삽입된 광섬유센서의 고장시 변형률이 급격히 낮아졌다.