• Structural Engineering and Mechanics
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• 제73권6호
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• pp.631-640
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• 2020

Using backup plate is one of the most commonly used methods to decrease drilling-induced delamination of composite laminates. It has been shown that, the size of the delamination zone is related to the vertical element of cutting force named as thrust force. Also, direct control of thrust force is not a routine task, because, it depends on both drilling parameters and mechanical properties of the composite laminate. In this research, critical feed rate and thrust force are predicted analytically for delamination initiation in drilling of composite laminates with backup plate. Three common theories, linear elastic fracture mechanics, classical laminated plate and mechanics of oblique cutting, are used to model the problem. Based on the proposed analytical model, the effect of drill radius, chisel edge size, and backup plate size on the critical thrust force and feed rate are investigated. Experimental tests were carried out to prove analytical model.

• 한국생산제조학회지
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• 제18권4호
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• pp.401-409
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• 2009

This paper presents a method of calculating the stress intensity factor (K) and crack propagation direction (${\theta}_0$) at the crack-tip that is associated with delamination in the large scale integration(LSI) package. To establish a reasonable strength evaluation method and life prediction, it is necessary to assess fracture parameters under various fracture conditions. Therefore, we conducted quantitative stress singularity analysis considering thermal stress simulating the changes of crack length (a), (h) and (v) in delamination using the 2-dimensional elastic boundary element method (BEM), and from these results predicted crack propagation direction and path.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
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• pp.35-38
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• 2002

Real defects in composite structures were detected by using laser measuring system. Four types of specimens, that is, a composite laminate, a honeycomb structure, a free-edge delamination and an adhesive joint, were used to study the applicability of ESPI and Shearography to composite structures. Thermal loading method, which can easily induce the surface deformation of specimen, was used to detect defects. Experimental results show that defects in composite structures can be easily detected by ESPI and Shearography. Moreover, it shows that ESPI and Shearography can be usefully applied to the detection of defects in various kinds of composite structures.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.94-102
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• 2007

Applications of bonded dissimilar materials such as large scale integration (LSI) packages, ceramics/metal and resin/metal bonded joints, are very increasing in various industry fields. It is very important to analyze the thermal stress and stress singularity at interface edge in LSI. In order to investigate stress singularities on the bonded interface edges and delamination of die pad and resin in the IC package. In this paper, stress singularity factors(${\Gamma}_i$) and stress intensity factors($K_i$) considering thermal stress in the IC package were analyzed by using the 2-dimensional elastic boundary element method(BEM).

• 대한기계학회논문집A
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• 제22권3호
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• pp.611-623
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• 1998

The delamination fracture of multidirectional carbon-fiber/epoxy laminates under the Mode I condition has been studied using the modified beam analysis for a fracture mechanics approach. It was found that the variation of fracture energy $G_IC$ with increasing length of the propagating crack exhibited a minimum for the pure interlaminar fracture and a maximum for the intraply fracture,i.e. a rising "R-curve", which was strongly affected by the degree of fiber bridging and crack-tip splitting arising in the global delamination. The maximum $G_IC$ value was significantly dependent on such types of delamination as no crack jumping, crack jumping into the adjacent ply and edge-delamination. It was shown also that the value of "effective flexural modulus" estimated from the modified beam analysis increased much with the development of fiber bridging behind the crack tip.ehind the crack tip.

• 대한기계학회논문집
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• 제18권8호
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• pp.2139-2157
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• 1994

In order to understand the delamination between leadframe and epoxy molding compound in an electronic packaging of surface mounting type, the stress intensity factor, T-stress and J-integral in fracture mechanics are obtained. The effects of geometry, material properties and molding process temperature on the delamination are investigated taking into account the temperature dependence of the material properties, which simulates as more realistic condition. As the crack length increases the J-integral increases, which suggest that the crack propagates if it starts growing from the small size. The effects of the material properties and molding process temperature on stress intensity factor, T-stress is and J-integral are less significant than the chip size for the practical cases considered here. The T-stress is negative in all eases, which is in agreement with observation that interfacial crack is not kinked until the crack approaches the edge of the leadframe.

• Composites Research
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• 제16권4호
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• pp.1-9
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• 2003

타이어 벨트층의 층간거동을 모사하기 위하여 2층 복합적층판을 고려하였다. 벨트층내의 층간전단응력 및 변형률을 측정하기위하여 3차원 유한요소해석을 수행하였다. 폭방향 전단변형률은 핀 이용법을 활용하여 측정되었다. 이들 실험 측정값은 적층판의 중앙부에서는 고전적층판이론과 그리고, 양가장자리부에서는 Kassapoglou 및 Kelsey의 이혼과 비교 하였다. 고무는 선형탄성체의 가정하였으며. 고투/코드 복한적층판은 직교이방성재질로 단순화 하였다 해석결과로부터, 층간박리의 원인인 층간전단응력은 고무내부의 양가장자리부에서 가장 큰 값을 보였다. 결과값은 중앙영역에서 고전적 층판이론과 매우 잘 일치하였으며. 양가장자리부에서는 이론값들과는 다소 차이를 보였다.

• Advanced Composite Materials
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• 제16권1호
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• pp.11-30
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• 2007

Since delamination often propagates at the interfacial layer between a surface skin and a foam core, a crack arrester is proposed for the suppression of the delamination. The arrester has a semi-cylindrical shape and is arranged in the foam core and is attached to the surface skin. Here, energy release rates and complex stress intensity factors are calculated using finite element analysis. Effects of the arrester size and its elastic moduli on the crack suppressing capability are investigated. Considerable reductions of the energy release rates at the crack tip are achieved as the crack tip approached the leading edge of the crack arrester. Thus, this new concept of a crack arrester may become a promising device to suppress crack initiation and propagation of the foam core sandwich panels.

• Computers and Concrete
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• 제2권6호
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• pp.481-498
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• 2005

A wavelet based approach is proposed for structural damage detection in beams, plate and delamination of composite plates. Wavelet theory is applied here for crack identification of a beam element with a transverse on edge non-propagating open crack. Finite difference method was used for generating a general displacement equation for the cracked beam in the first example. In the second and third example, damage is detected from the deformed shape of a loaded simply supported plate applying the wavelet theory. Delamination in composite plate is identified using wavelet theory in the fourth example. The main concept used is the breaking down of the dynamic signal of a structural response into a series of local basis function called wavelets, so as to detect the special characteristics of the structure by scaling and transformation property of wavelets. In the light of the results obtained, limitations of the proposed method as well as suggestions for future work are presented. Results show great promise of wavelet approach for damage detection and structural health monitoring.

• Structural Engineering and Mechanics
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• 제31권4호
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• pp.407-421
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• 2009

The present paper addresses the optimal design of composite laminates with the aim of minimizing free-edge delamination stresses. A technique involving the application of particle swarm optimization (PSO) integrated with FEM was developed for the optimization. Optimization was also conducted with the zero-order method (ZOM) included in ANSYS. The semi-analytical method, which provides an approximation of the interlaminar normal stress of laminates under in-plane load, was used to partially validate the optimization results. It was found that optimal results based on ZOM are sensitive to the starting design points, and an unsuitable initial design set will lead to a result far from global solution. By contrast, the proposed method can find the global optimal solution regardless of initial designs, and the solutions were better than those obtained by ZOM in all the cases investigated.