• 한국해양공학회지
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• 제12권3호통권29호
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• pp.31-41
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• 1998

Single fiber fragmentation technique was used to evaluate the change of interfacial properties by degradation of fiber tensile strength in the fiber reinforced composites. The influences of fiber tensile strength on the interfacial properties have been evaluated by the fragmentation specimens(weak fiber samples) of glass fiber/epoxy resin that was made using the pre-degraded glass fiber in distilled water at $80^{circ}C$ for specified periods. The effects of the immersion time on the interfacial properties in the distilled water at $80^{circ}C$ also have been evaluated by the fragmentation specimens(original fiber samples) of glass fiber/epoxy resin that was made using the received glass fiber. As the result, the tensile strength of glass fiber was decreased with the increasing of the treatment time in the distilled water at $80^{circ}C$ and the interfacial shear strength was independent of the change of the glass fiber strength in the single fiber fragmentation test. But in the durability test using the single fiber fragmentation specimen, interfacial shear strength decreased with the increasing of the immersion time in distilled water ar $80^{circ}C$. And it turned out that the evaluating of interfacial shear strength using original fiber tensile strength was valuable in the durability test for the water environment by the single fiber fragmentation technique.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.159-162
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• 2000

Interfacial and microfailure properties of carbon fiber/epoxy matrix composites were evaluated using both tensile fragmentation and compressive Broutman tests with acoustic emission (AE). Amino-silane and maleic anhydride polymeric coupling agents were used via the dipping and electrodeposition (ED), respectively. Both coupling agents exhibited higher improvements in interfacial shear strength (IFSS) under tensile tests than compressive cases. However, ED treatment showed higher IFSS improvement than dipping case under both tensile and compressive test. The typical microfailure modes including fiber break, matrix cracking, and interlayer failure were observed during tensile test, whereas the diagonal slippage in fiber ends was observed during compressive test. For both the untreated and treated cases AE distributions were separated well under tensile testing. On the other hand, AE distributions were rather closer under compressive tests because of the difference in failure energies between tensile and compressive loading. Under both loading conditions, fiber breaks occurred around just before and after yielding point. Maximum AE voltage fur the waveform of carbon or basalt fiber breakage under tensile tests exhibited much larger than those under compressive tests.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.79-83
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• 2000

Interfacial and microfailure properties of carbon liber/bismaleimide (BMI) composites were evaluated using both tensile fragmentation and compressive Broutman tests with acoustic emission (AE). Since BMI is rather difficult matrix to apply for the conventional fragmentation test because of its too low elongation and too brittle and high modulus properties, dual matrix composite system was applied. After carbon fiber/BMI composite was prepared for rod shape by controlling differing curing stage, composites rod was embedded in toughened epoxy as outer matrix. The typical microfailure modes including fiber break, matrix cracking, and interlayer failure were observed during tensile testing, whereas the diagonal slippage in fiber ends was observed during compressive test. On the other hand, AE amplitudes of BMI matrix fracture were higher than carbon fiber tincture under tensile test because BMI matrix has very brittle and high modulus. The waveform of signals coming from BMI matrix fractures was consistent with AE amplitude result under tensile tests.

• Macromolecular Research
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• 제10권1호
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• pp.24-33
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• 2002

Interfacial and microfailure properties of carbon fiber/epoxy composites were evaluated using both tensile fragmentation and compressive Broutman tests. A monomeric and two polymeric coupling agents were applied via the electrodeposition (ED) and the dipping applications. A monomeric and a polymeric coupling agent showed significant and comparable improvements in interfacial shear strength (IFSS) compared to the untreated case under both tensile and compressive tests. Typical microfailure modes including cone-shaped fiber break, matrix cracking, and partial interlayer failure were observed under tension, whereas the diagonal slipped failure at both ends of the fractured fiber appeared under compression. Adsorption and shear displacement mechanisms at the interface were described in terms of electrical attraction and primary and secondary bonding forces.

• Geomechanics and Engineering
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• 제15권5호
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• pp.1047-1059
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• 2018

This paper focuses on the cracking and fragmentation process in rock materials containing a pair of non-parallel flaws, which are through the specimen thickness, under vertical compression. Several numerical experiments are conducted with varying flaw arrangements that affect the initiation and tensile wing cracks, shear crack growth, and crack coalescing behaviors. To obtain realistic numerical results, a parallelized peridynamics formulation coupled with a finite element method, which is able to capture arbitrarily occurring cracks, is employed. From previous studies, crack initiation and propagation of tensile wing cracks, horsetail cracks, and anti-wing cracks are well understood along with the coalescence between two parallel flaws. In this study, the coalescence behaviors, their fragmentation sequences, and the role of an x-shaped shear band in rock material containing two non-parallel flaws are discussed in detail on the basis of simulation results strongly correlated with previous experimental results. Firstly, crack initiation and propagation of tensile wing cracks and shear cracks between non-parallel flaws are investigated in time-history and then sequential coalescing behavior is analyzed. Secondly, under the effect of varying inclination angles of two non-parallel flaws and overlapping ratios between a pair of non-parallel flaws, the cracking patterns including crack coalescence, fragmentation, and x-shaped shear band are investigated. These numerical results, which are in good agreement with reported physical test results, are expected to provide insightful information of the fracture mechanism of rock with non-parallel flaws.

• Composites Research
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• 제13권4호
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• pp.54-66
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• 2000

탄소섬유/에폭시 복합재료의 계면 및 미세파괴 물성을 인장 fragmentation과 압축 Broutman 두 시험법과 음향방출 시험을 이용하여 평가하였다. Maleic anhydride polymeric coupling agent와 amino-silane를 각각 전기증착법 및 dipping을 통하여 섬유표면에 적용하였다. 두 coupling agents를 사용한 섬유와 기지간의 계면전단강도는 인장 및 압축 두 시험에서 모두 미처리와 비교하여 큰 증가를 나타내었다. 인장시험 동안에, 원추모양의 섬유파단과 기지의 cracking 그리고 부분적인 interlayer failure로 이루어진 전형적인 미세파괴 형태가 발생하였다. 이에 비하여, 압축시험에서는 부러진 섬유의 끝에서 대각선 방향이 슬립거동이 관찰되었다. 주어진 두 힘의 하중상태에서 섬유의 파단은 항복점 전후 부근에서 일어났다. 음향방출분포는 인장에서 섬유표면 처리와 미처리의 두 조건에서 미세파괴 신호가 잘 분리되었으며, 한편, 압축에서는 signal이 다소 중복되어 나타났다. 이는 탄소섬유의 인장력/압축력 간의 파괴에너지 차이에 기인한다고 고려된다. 탄소와 basalt 섬유복합재료의 섬유파단 waveform의 최대 voltage는 압축보다 인장시험에서 상당히 크게 나타났으며, 이들은 음향방출시험으로 파괴에너지 차이를 명확히 비교 및 확인할 수 있었다.

• Structural Engineering and Mechanics
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• 제82권6호
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• pp.713-724
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• 2022

Effects of coal tensile strength and plow configuration on the coal fragmentation process was modeled by two-dimensional particles flow code (PFC2D). Three tensile strength values, 0.5, 1,5 and 3.5 MPa were considered in this numerical study. The cutters of plow penetrated in the coal for 4 mm at a rate of 0.016 m/s. According to the PFC manual, the local damping factor was 0.7. Three failure mechanism of coal during the fragmentation process by plow were modelled. The coal material beneath the cutters showed the elastic, plastic and fracturing behaviors in this analysis. In all the models, the plastic zone was fractured and some micro-cracks were induced but the elastic zone remained undamaged. It was observed that the tensile strength affected the failure mechanism of coal significantly and as it increased the extent of the fractured zone underneath the plow cutter decreased during the fragmentation process.

• Geomechanics and Engineering
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• 제18권2호
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• pp.111-119
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• 2019

Due to certain geological characteristics (high thickness, rocky properties), some underground coal mines require the use of explosives. This paper explores the effects of fragmentation of different decks detonated simultaneously in a single borehole with the use of numerical analysis. ANSYS/LS-DYNA code was used for the implementation of the models. The models include an erosion criterion to simulate the cracks generated by the explosion. As expected, the near-borehole area was damaged by compression stresses, while far zones and the free surface of the boundary were subjected to tensile damage. With the increase of the number of decks in the borehole, different changes in the fracture pattern were observed, and the superposition effects of the stress wave became evident, affecting the fragmentation results. The superposition effect is more evident in close distances to the borehole, and its effect attenuates when the distance to the borehole increase.

• Advanced Composite Materials
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• 제17권1호
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• pp.75-87
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• 2008

Aerospace structural applications, along with high performance marine and automotive applications, require high-strength efficiency, which can be achieved using metal matrix composites (MMCs). Rotating components, such as jet-engine blades and gas turbine parts, require materials that maximize strength efficiency and metallurgical stability at elevated temperatures. Titanium matrix composites (TMCs) are well suited in such applications, since they offer an enhanced resistance to temperature effects as well as corrosion resistance, in addition to optimum strength efficiency. The overall behavior of the composite system largly depends on the properties of the interface between fiber and matrix. Characterization of the fiber.matrix interface at operating temperatures is therefore essential for the developemt of these materials. The fiber fragmentation test shows good reproducibility of results in determining interface properties. This paper deals with the evaluation of fiber fragmentation characteristics in TMCs at elevated temperature and the results are compared with tests at ambient temperature. It was observed that tensile testing at $650^{\circ}C$ of single-fiber TMCs led to limited fiber fragmentation behavior. This indicates that the load transfer from the matrix to the fiber occurs due to interfacial friction, arising predominantly from mechanical clamping of the fiber by radial compressive residual and Poisson stresses. The present work also demonstrates that composite processing conditions can significantly affect the nature of the fiber.matrix interface and the resulting fragmentation of the fiber.

• 접착 및 계면
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• 제2권1호
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• pp.9-17
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• 2001

전기저항 측정법과 인장 및 압축 시험을 이용하여, 탄소섬유/에폭시 복합재료의 정화특성과 계면물성을 평가하였다. 계면이 존재하지 않는 탄소섬유 자체만을 사용했을 경우에는 경화 초기와 최종단계의 저항차이는 없었으며, 계면이 존재하는 탄소섬유/에폭시 시편의 경우에는 매트릭스 경화 수축에 의해 저항차가 크게 나타났다. 인장 하충하의 저항 변화 측정에서, 전기증작된 시편은 섬유의 첫 파단에 의해 저항이 무한대로 도달하는 시간이 미처리에 비해 다소 지연되는 현상을 보였다. 인장 및 압축 시험에서 표면처리된 시연은 미처리섬유에 비해 계면전단 강도가 현저히 크게 증가하였다. 인장의 경우, 미처리 섬유에서는 debonding 형태, 그리고 표면처리된 섬유에서는 cone 형태의 판단이 관찰되었다. 압축에서는 부러진 섬유 끝에서 대각선으로 미끄러지는 파단 현상이 두 경우 모두에서 나타났는데, 미처리섬유는 창 끝과 같은 예리한 파단이 일어나며, 전기증착된 섬유는 다소 둔한 판단이 나타났다. 이를 통해 전기증착에 의한 표면처리가 계면접착력과 미세파괴구조에 인장 및 압축하에서 각각 다른 영향을 주는 것을 확인하였다.