• Composites Research
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• v.22 no.3
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• pp.82-88
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• 2009

The effect of open and filled holes on the strength behavior of carbon fiber reinforced polymeric (CFRP) composites was investigated. The strength was measured at room temperature dry, cold temperature dry, $-55^{\circ}C$, and elevated temperature wet, $108.3^{\circ}C$ on several different laminate configurations. Based on the experimental data presented, it is shown that the filled hole tensile strength is larger than that of open hole by reducing damage around the hole due to the constraint imposed by the fastener. The tensile strength at cold temperature dry, $-55^{\circ}C$ is increased with the brittleness by the thermal expansion coefficient of fiber and matrix. The compressive strength at elevated temperature wet, $108.3^{\circ}C$ is decreased by the cause of interfacial deterioration between fiber and matrix with moisture absorption.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.29-29
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• 1997

각광 받는 구조재료인 섬유강화 복합적층재에 대한 기계적 체결 거동은 본질적인 재료의 이방성에 의해서 파단강도가 파단 모우드와 매우 밀접한 관련을 갖는 것으로 알려져 있다. 따라서, 복합적층판 체결부의 정밀 구조 설계에서는 단순화에 따른 오차를 줄이고 정밀해에 의한 설계 및 해석이 요청된다. 특히, 층간응력 성분을 무시할 수 없는 두께를 갖는 복합적층 판의 기계적 체결부 해석이나 실제 구조물의 체결부에서 발생하는 굽힘이나 비틀림과 같은 하중 상태를 묘사하기 위해서도 정밀한 3차원 응력 해석은 필요하다. 하지만, 지금까지 기계적 체결부의 거동에 관한 연구는 층간응력 성분들을 어느정도 무시할 수 있는 얇은 평판에 대한 2차원 응력해석에 주로 국한되어 왔으며, 일부 수행된 체결부에 대한 3차원 응력 해석의 경우 여러 단점을 갖는 3차원 연속체 요소에 의한 유한요소 해석이 수행되었을 뿐이다.본 연구는 층간응력 성분들을 무시할 수 없는 두께를 갖는 복합적층판의 기계적 체결부 해석에 지금까지 사용되어온 3차원 연속체 요소에 의한 유한요소 방법이 갖는 단점들을 개선한 Layerwise 유한요소법을 이용하여 3차원 응력해석을 수행하였다. 특히, 선형상보성원리에 근거한 최적설계 기법을 응용하여, 기계적 체결시 핀과 적층판의 홀 사이에 발생하는 하중 전달 과정을 모사하고, 접촉력에 의한 홀 주위의 복잡하고 국부적인 응력 집중현상을 규명하여본다.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.5 s.182
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• pp.149-154
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• 2006

The cold expansion method (CEM) is one of the widely used a method to improve the fatigue behavior of materials in aerospace industry. Such improvement is due to the compressive residual stress developed when a tapered mandrel goes through the fastener holes a little smaller than the mandrel. CEM is retarded of crack initiation due to the compressive residual stress developed on the hole surface. Many researchers are studied a finite element analysis of residual stress around fastener hole. But in case of real model, fastener hole has a clamping force after CE. Therefore, it is respected that residual stress distributions should be changed due to clamping forces. In this paper, it was performed finite element analysis of residual stress by clamping force after CE in the plate having adjacent holes. From this study, it has been found that compressive residual stress near the hole increases according to clamping force. Also, the more increase clamping force, the more increases compressive residual stress. However, tensile residual stress increase beyond clamping force area.

• Composites Research
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• v.23 no.3
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• pp.1-6
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• 2010

Recently, CFRP composite is more and more used in the various fields because of a higher specific modulus, chemical property and so on. Most products using CFRP composite are manufactured by construction of components. Various components are joined with those by bolts and pins. Holes for bolts and pins decrease strength and fatigue life of components, because those act as notch in structures. In this paper, we experimentally evaluated the fatigue life of hole-notched and unnotched weave CFRP plate. Then, we compared the two results and proposed an equation for prediction of fatigue life.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.79-84
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• 2003

Cold expansion of fastener holes is a mechanical process widely used in the aerospace industry. This treatment leads to an improvement of fatigue behavior due to the developed compressive residual stresses on the hole surface. Despite its importance to aerospace industries, little attention has been devoted to the accurate modeling of the process. This study is devoted to the modeling and simulation of the residual stress resulting from the cold expansion of two adjacent fastener holes. Simultaneous cold expansion of two adjacent holes lead to much higher compressive residual stress than sequential cold expansion.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.304-310
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• 2001

Cracks at mechanical fastener holes usually nucleate as elliptical comer cracks at the faying surface of the mechanical joints and grow as elliptical arc through cracks after penetrating the opposite surface. In this study mode I, II and III stress intensity factors at two surface points of elliptical arc through cracks at mechanical fastener holes are analyzed by applying weight function method. The weight function method for two dimensional mixed-mode problem is extended to three dimensional one and it is verified.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.2
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• pp.46-51
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• 2002

Cold expansion of fastener holes is a mechanical process widely used in the aerospace industry. This treatment leads to an improvement of fatigue behavior due to the developed compressive residual stresses on the hole surface. The residual stress profile depends on the parameters of cold expansion, which are expanding rate, inserting direction of mandrel, material properties dtc. Despite its importance to aerospace industiries, little attention has been devoted to the accurate modeling of the process. In this paper, three-dimensional finite element simulations have been conducted for the cold expansion in an aluminium plate in order to predict the magnitude and distribution of the residual stress. To prove the results of FE analysis, the residual strain was measured by strain gage in cold expansion test. Maximum compressive residual stress could be increase about 7 percentage using the 2-step cold expansion method.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.419-424
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• 2001

The purpose of this study is comparing cold expansion method with interference fit. Cold expansion method and interference fit of fastener hole is using in the aerospace industry. These treatment lead to an improvement of fatigue life to the compressive residual stresses developed on the hole surface. But Research is nothing to about difference effect of between cold expansion method and interference fit. So In this paper, It is shown that Comparing cold expansion method with interference fit. and It is further shown that residual stress distribution according to plate thickness.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.603-608
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• 2001

Recently, cold expansion of fastener holes is commonly used in the aerospace industry to increase the fatigue endurance of airframes. Cold expansion process is used as the retardation of crack initiation in the hole. This treatment leads to an improvement of fatigue behavior due to the compressive residual stresses developed on the hole surface. The residual stress profile depends on the cold expansion ratio. In the present paper, it is shown that residual stress is redistributed due to the application of cold expansion process for CT specimen. It is further shown that residual stress increases in proportion to cold expansion ratio. It is thought that crack growth rate increases as cold expansion ratio.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.470-474
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• 2000

Cold expansion of fastener holes is a mechanical process widely used in the aerospace industry. This treatment leads to an improvement of fatigue behavior due to the developed compressive residual stresses on the hole surface. The residual stress profile depends on the parameters of cold expansion, which are, expanding rate, inserting direction of mandrel, material properties etc. and the method to confirm this profile is only measurement by X-ray diffractometer. Despite its importance to aerospace industries, little attention has been devoted to the accurate modelling of the process. In this paper, Two-dimensional axisymmetric finite element simulations have been conducted for the cold expansion in an aluminium plate in order to predict the magnitude and distribution of the residual stress and plastic deformation. Maximum compressive residual stress could be increase about 7 percent using the 2-step cold expansion method.