• 한국안전학회지
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• 제28권1호
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• pp.12-17
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• 2013

Considering the wind power system and the rotor blades which are composed of much technology, the wind power blade would be the most dangerous part because it revolves at high speed and weighs about dozens of tons, if the accident happens. Therefore, the light weight composite materials have been replacing as substitutional materials. The object of this study is to examine the delamination and damage for CFRP/GFRP hybrid composite that is used for strength improvement of a wind power blade. The influence of the initial crack length and fiber orientation for the interlaminar delamination was exposed for the blade safety. Plain woven CFRP instead of GFRP was inserted into the layer of the box spar for improving the strength and blade life. DCB(Double Cantilever Beam) specimen was used for evaluating fracture toughness and damage evaluation of interlaminar delamination. The material used in the experiment is a commercial material known as CF 3327 EPC in plain woven carbon prepreg(Hankuk Carbon Co.) and UD glass fiber prepreg(Hyundai Fiber Co.). From the results, crack growth rate is not so different according to the variation of the initial crack length. Mode I interlamainar fracture toughness of fiber direction $0^{\circ}$ is higher than that of $45^{\circ}$. Interlaminar fracture has an effect on fiber direction and K decreased with lower value according to increasing initial crack length. Also energy release rate fracture toughness was evaluated because CFRP/GFRP hybrid composite with a different thickness is under the mixed mode loading condition. The interlaminar fracture was almost governed by mode I fracture even though the mixed mode.

• International Journal of Precision Engineering and Manufacturing
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• 제9권4호
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• pp.66-70
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• 2008

The propagation of a mixed-mode crack in soda-lime silica glass is modeled by movable cellular automata (MCA). In this model, a special fracture criterion is used to describe the process of crack initiation and propagation. The results obtained using the MCA criterion are compared to those obtained from other crack initiation criteria, The crack resistance curves and bifurcation angles are determined for various loading angles. The MCA results are in close agreement with results obtained using the maximum circumferential tensile stress criterion.

• 대한기계학회논문집A
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• 제21권3호
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• pp.423-429
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• 1997

A simplified method for determining the mode components of the strain energy release rate of free-edge delaminations in laminated composite is proposed. The interlaminar stresses are evaluated as an interface moment and interface shear forces that are obtained from the equilibrium equations at the interface between the adjacent layers. Deformation of an edge-delaminated laminate is calculated by using a generalized quasi-three dimensional classical laminated plate theory developed by the authors. The analysis provides closed-form expression for the three components of the strain energy release rate. Comparison of results with a finite element solution using the virtual crack closure technique shows good agreement. In the present study, laminated composite with stacking sequences of [30/-30/90]$_{s}$ were examined. The simple nature of the method makes it suitable for primary design analysis for the delaminations of laminated composite.e.

• Structural Engineering and Mechanics
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• 제87권1호
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• pp.47-56
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• 2023

Any pre-existed delamination defect present during manufacturing or induce during service loading conditions in the wingskin adherend invariably shows a greater loss of structural integrity of the spar wingskin joint (SWJ). In the present study, inter-laminar delamination propagation at the critical location of the SWJ has been carried out using contact and multi-point constraint finite elements available with commercial FE software (ANSYS APDL). Strain energy release rates (SERR) based on virtual crack closure technique have been computed for evaluation of the opening (Mode-I), sliding (Mode-II) and cross sliding (Mode-III) modes of delamination by sequential release of multi point constraint elements. The variations of different modes of SERR are observed to be significant by considering varied delamination lengths, material properties of adherends and radius of curvature of the SWJ panel. The SERR rates are seen to be much different at the two pre-embedded delamination ends. This shows dissimilar delamination propagation rates. The maximum is seen to occur in the delamination front in the unstiffened region of the wingskin. The curvature geometry and material anisotropy of SWJ adherends significantly influences the SERR values. Increase in the SERR values are observed with decrease in the radius of curvature of wingskin panel, keeping its width unchanged. SWJs made with flat FRP composite adherends have superior resistance to delamination damage propagation than curved composite laminated SWJ panels. SWJ made with Boron/Epoxy (B/E) material shows greater resistance to the delamination propagation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.3-8
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• 2001

Dynamic stress intensity factors (DSIFs) are obtained when a crack propagates with constant velocity in rectangular functionally gradient materials (FGMs) under dynamic mode III load. To obtain the dynamic stress intensity factors, it is used the general stress and displacement fields of FGMs for propagating crack and the boundary collocation method (BCM). The stress intensity factors and energy release rates are the greatest in the increasing properties $(\xi>0)$, next constant properties $(\x=0)$ and decreasing properties $(\xi<0)$ under constant crack tip properties and crack tip speed.

• Structural Engineering and Mechanics
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• 제55권1호
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• pp.191-204
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• 2015

Control of the mechanical behavior of composite materials and structures under monotonic and dynamic loads for cracks and damage is a vast and complex area of research. The modeling of the different physical phenomena and behavior characteristics of a composite material during deformation play an important role in the structural design. Our study aims to analyze numerically the energy release rate parameter G of a composite laminated plate (glass or boron / epoxy) cross-ply [$+{\alpha}$, $-{\alpha}$] in the presence of a crack between two circular notches under the effect of several parameters such as fiber orientation ${\alpha}$, the crack orientation ${\beta}$, the orientation ${\gamma}$ of the two considered circular notches and the effect of mechanical properties. Our results show clearly that both notches orientation has more effect on G than the cracks and fibers orientations.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.206-213
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• 2013

본 논문에서는 적분변환법을 이용하여 면외전단 충격하중이 작용하는 두 개의 서로 다른 압전재료층 사이의 기능경사압전재료 접합층 내부 균열에 대한 과도응답 해석 을 수행한다. 기능경사압전재료의 물성치는 두께 방향을 따라 연속적으로 변하는 것으로 가정한다. 라플라스 변환과 푸리에 변환을 이용하여 문제를 복합적분방정식으로 구성하고, 수치해석을 위해 복합적 분방정식을 제 2 종 프레드홀름 적분방정식으로 표현한다. 전기적 하중, 재료물성 치의 변화율, 각 접합층의 두께가 균열의 과도응답에 미치는 영향을 보기 위해 동에너지 해방률에 대한 수치해석 결과를 제시한다.

• Composites Research
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• 제21권4호
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• pp.7-14
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• 2008

접착제 이용 결합 조인트의 하중지지 능력 예측 기법은 점착제를 이용한 접합 조인트 설계에 있어서 가장 중요한 기술이다. 본 연구 계면 파괴역학을 이용하여 복합재료/금속 접착 조인트의 하중지시 능력을 예측하는 기법을 소개한다. 구체적으로 복합재료/탄소강 결합의 접착 강도를 계면 균열의 에너지 방출률과 계면 파괴인성치 개념을 사용하여 평가하는 방법을 제시 검증하였다. 계면 균열의 에너지 방출률은 유한요소해선 결과를 이용한 가상 균열 닫음 기법 (VCCT)을 사용하여 계산하였으며, 게면 파괴인성치는 이종재료 ENF (end-notched flexure) 시편을 고안하여 측정하였다. 고안된 이종 재료 ENF 시편을 사용하여 시편의 두께에 상관없이 일관된 Mode II 계면 파괴인성치를 측정할 수 있음과 양면 겹치기 접합 조인트의 특성 에너지 방출률이 측정된 계면 파괴인성치와 일치함을 확인하였다. 따라서 에너지 방출률에 근거한 계면 균열 진전 기준은 접착 조인트의 하중지지 능력을 신뢰성 있게 예측하는 실제적인 설계 도구로서 활용될 수 있다.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2172-2179
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• 2002

In this paper, we examine the dynamic electromechanical behavior of an edge crack in a piezoelectric ceramic layer bonded between two elastic layers under the combined anti-plane mechanical shear and in-plane electric transient loadings. We adopted both the permeable and impermeable crack boundary conditions. Fourier transforms are used to reduce the problem to the solution of two pairs of dual integral equations, which are then expressed to a Fredholm integral equation of the second kind. Numerical values on the dynamic energy release rate are presented to show the dependences upon the geometry, material combination, electromechanical coupling coefficient and electric field.

• Composites Research
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• 제16권5호
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• pp.45-53
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• 2003

본 논문에서는 이차 본딩으로 접착된 복합재료-복합재료 Single-Lap 조인트 시편에 대해 인장 시험 및 수치해석을 통해 그 파손 특성을 조사하였다. 시편시험에서는 시험 중에 CCD 카메라 및 AE 센서를 이용해 초기 균열의 발생 및 진전양상에 대한 시험적인 관찰을 수행하였다. 시편에 대해 기하비선형 유한요소해석 및 VCCT(Virtual Crack Closure Technique)기법을 이용해 시편의 거동 및 변형율에너지방출률을 계산하고 세 가지 관찰된 초기 균열 모드에 대해 파손강도를 계산하였다. 인장시험에서 초기 균열은 모서리 계면 균열, 측면 계면 균열 및 층간 분리 균열의 세 가지 형태로 최종 파손의 60∼90% 하중에서 발생하였다. 주된 파손 모드는 접착제 계면 파손(adhesive failure) 및 적층판의 첫 번째 및 두 번째의 층간 분리 파손이었다. 두꺼운 접착제 층을 갖는 시편들은 초기균열이 낮은 하중에서 발생하였지만 균열진전에 대한 저항성 및 파손하중은 높게 나타났다. 층간분리파손은 주로 두꺼운 접착제의 경우에 발생하였다. 세 가지 초기 균열 모드에 대해 변형률에너지방출률은 Mode I의 G값이 Mode II의 G값보다 크게 계산되었다. Mode I 및 전체 G값은 측면 계면 균열, 모서리 계면 균열, 층간분리 균열의 순서로 크게 계산되었다.