• Composites Research
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• 제26권2호
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• pp.129-134
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• 2013

극저온 환경에 노출되는 구조체의 접착조인트의 경우 피접착물과 접착물 사이에서 열팽창계수 차이로 인해 계면에서 잔류응력이 발생하게 되는데 이에 의해 접착조인트 내부에 미소균열, 층간분리 등의 형태로 파손이 발생할 우려가 있다. 본 연구에서는 높은 비강성, 낮은 열팽창계수의 특성을 지닌 메타 아라미드 섬유를 에폭시 기지재의 보강재로 사용하였다. 표면처리 공정을 간소화하기 위해 전기방사법의 고분자 혼합법(polymer blend method)으로 코어-쉘 구조의 메타 아라미드/에폭시 나노섬유를 제조하였다. 극저온 환경에서 계면특성이 향상된 코어-쉘 구조의 나노섬유를 보강한 에폭시 접착제의 전단물성을 확인하기 위해 환경챔버를 이용하여 $-150^{\circ}C$의 저온에서 단일 겹치기 실험(single lap joint test)을 진행하였다. 또한, DCB(double cantilever beam) 실험을 통해 파괴인성을 측정하였다. 그 결과, 극저온에서 일반 메타 아라미드 나노섬유에 비해 코어-쉘 구조의 메타 아라미드/에폭시 나노섬유를 보강한 접착제 시편이 우수한 계면특성으로 인해 물성이 크게 향상되었음을 확인하였다.

• Journal of Welding and Joining
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• 제30권3호
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• pp.15-20
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• 2012

Diagnosing and improving adhesion of advanced packaging and thin films is an essential part of the research and development in microelectronics. In this paper, the four-point bend test and the double cantilever beam test among various adhesion measurement methods are reviewed.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1547-1556
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• 2000

In this paper, an evaluation method of fracture toughness to apply interfacial fracture mechanics was investigated in adhesively bonded double-cantilever beam (DCB) joints. Four types of adhesively bonded DCB joints with an interface crack were prepared for analyses of the stress intensity factors using boundary element method(BEM) and the fracture toughness test. From the results of BEM analysis and fracture toughness experiments, it is found that the stress intensity factor, K1 is a parameter driving the fracture of adhesively bonded joints. Also, the evaluation method of fracture toughness by separated stress intensity factors of mixed mode cracks was proposed and the influences of mode components for its fracture toughness are investigated in adhesively bonded DCB joints.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2213-2222
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• 1996

This paper presents the design process and evaluaation results of a two-axis force transducer for measuring flange reaction forces. A double-cantilever beam structure is used as a sensing element, and its optimal configuration is determined based on the derived strain equations to maximize the sensitivity and minimize the regid body displacements. To reduce the coupling errors between two-axis forces, strain distributions by finite elemetns analysis are utilized and the Wheaststone bridge cricuits composed of strain gages are built such that the output voltage should be zero, although strains of four strain gages are not zero. Calibration test shows that the two-azxis force transducer developed in this paper is useful in measuring flange reaction forces within the coupling error of 5.53%.

• 한국산학기술학회논문지
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• 제13권4호
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• pp.1488-1495
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• 2012

본 논문에서는 알루미늄 폼 복합재료로 된 DCB(이중외팔보) 시험편의 파괴 거동을 시뮬레이션 해석하였다. 시뮬레이션 해석에 사용된 모델은 영국 공업규격과 ISO국제규격에 의거한 3D 형태로 하였다. 모델의 두께가 두꺼울수록 발생한 크랙의 길이가 길게 나타났고, 높은 하중이 발생하였다. 본 연구에서 얻어진 해석 결과를 알루미늄 폼재질로 접합된 실제 복합재 구조물에 적용시켜 파괴거동을 분석하고 그 기계적인 특성을 파악할 수 있다.

• 한국세라믹학회지
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• 제33권5호
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• pp.602-615
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• 1996

The purpose of the present study is to investigate the microstructural effect on the R-curve behavior in three aluminas with different grain size distributions by analyzing the bridging stress distribution. The crack opening displacement (COD) according to the distance behind the stationary crack tip was measured using an in situ SEM fracture method. The measured COD values in the fine-grained alumina agreed well with Wiederhorn's sollution while they deviated from Wiederhorn's solution in the two coarse-grained aluminas because of the increase of the crack closure due to the grain interface bridging in the crack wake. A numerical fitting procedure was conducted by the introduction of the power-law relation and the current theoretical model together with the measured COD's in order to obtain the bridging stress distribution. The results indicated that the bridging stress function and the R-curve computed by the current model were consistent with those computed by the power-law relation providing a reliable evidence for the bridging stress analysis of the current model. The strain-softening exponent in the power-law relation n, was calculated to be in the range from 2 to 3 and was closely related to the grain size distribution. Thus it was concluded from the current theoretical model that the grain size distribution affected greatly the bridging stress distribution thereby resulting in the quantitative analysis of microfracture of polycrystalline aluminas through correlating the local-fracture-cont-rolling microstructure.

• 대한기계학회논문집A
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• 제24권7호
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• pp.1863-1870
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• 2000

When an impact stress is applied on the external boundary of double cantilever beam of orthotropic material which crack length is greater than specimen hight and anistropic ratio is very high, dyna mic energy release rate is derived, and the relationship between dynamic energy release rate and crack propagating velocity is studied. Dynamic energy release rate to static energy release rate is decreased with increasment of crack propagating velocity. The relationships between dynamic energy release rate and vertical strain have a similar pattern with those between static energy release rate and vertical strain. When normalized time(Cstla) is greater than or equal to 2, dynamic energy release rate approaches to a constant value.

• Composites Research
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• 제32권2호
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• pp.102-107
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• 2019

Several studies related to reinforce composites structures in the through thickness direction have been developed along the years. As follows, in this study a new reinforced process is proposed based on previous experimental results using a novel stitching process in T-joints and one-stitched specimens. It was established the need to perform more analysis under standard test methods to obtain a better understanding. FEM analysis were compared after performed mode I interlaminar fracture toughness test, using different stitching patterns to analyze the through thickness strength with reference laminates without stitching. The stitching patterns were defined in $2{\times}2$ and $3{\times}3$, where the upper and lower head of the non-continuous stitching process (I-Fiber) has proven to influence in a higher through thickness strength of the laminate. In order to design the numerical model, cohesive parameters were required to define the surface to surface bonding elements using the cohesive zone method (CZM) and simulate the crack opening behavior from the double cantilever beam (DCB) test.

• 콘크리트학회논문집
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• 제13권2호
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• pp.153-160
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• 2001

본 연구에서는 콘크리트 부재에서의 축압축강도에 대한 크기효과를 검토하였다. 이를 위하여 두 가지 대표적인 압축파괴모드 중의 하나인 모드 I 파괴에 대한 실험적 연구를 이중 캔틸레버 보를 이용하여 수행하였다. 각 캔틸레버의 축에 대한 작용하중의 편심거리와 초기 균열길이를 변화시킴에 의하여 콘크리트의 축압축강도에도 크기효과가 존재하는 지의 여부를 확인하였고, 최소자승법을 이용하여 수정된 크기효과법칙의 새로운 실험상수들을 제시하였다. 연구결과로부터 초기 균열이 있는 콘크리트 부재의 축압축강도에도 크기효과가 존재함을 확인하였다. 하중의 편심거리에 있어서는 균열선단에서의 인장과 압축응력의 영향이 매우 중요하며 이 경우에 뚜렷한 크기효과가 나타났다. 즉 균열선단에서 인장응력의 영향이 증가하면 콘크리트의 크기효과는 증가한다. 그러나 초기 균열길이의 경우, 축압축강도의 크기효과에 미치는 영향은 존재하지만 균열길이에 따른 차이는 뚜렷하지 않았는데 이는 고강도 콘크리트 부재의 경우 부재의 세장비 차에도 불구하고 파괴진행영역의 크기가 서로 비슷한데 그 원인이 있는 것으로 판단된다.

• 수산해양기술연구
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• 제35권4호
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• pp.410-420
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• 1999

The value of the mode I interlamina fracture toughness, GIC, is calculated by experimental compliance method, modified compliance method and beam theory. The value of the mode II interlamina fracture toughness, GIC, is evaluated by beam method, theory beam theory and compliance method. This paper describes the effect of load pint displacement rate and speicimen geometries for mode I and II interlaminar fracture toughness of glass fiber reinforced plastic composites by using double cantilever beam (DCB) and end notched flexure (ENF) specimen. For the load point displacement rate of increases whereas the value of 2,6 and 10 mm/min the value of GIC decrease as load point displacement rate increases whereas the value of GIC is found to be no significant effect. The value of GIC decreases as initial crack length increases. The fractured surface of the DCB and ENF samples are examined by scanning electron microscopy (SEM).