• 동력기계공학회지
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• 제14권3호
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• pp.52-57
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• 2010

Interlaminar stresses near the free edges of composite laminates have been analyzed considering wall effects. Interface modeling of bonding layer was introduced to explain the wall effect. Using Lekhnitskii stress functions and the principle of complementary virtual work, the interlaminar stresses were obtained, which satisfied the traction free boundary conditions not only at the free edges, but also at the top and bottom surfaces of laminates. The interface modeling provides not singular stresses but concentrated finite interlaminar stresses. The significant amount of reductions of stresses at the free edge are observed compared to the results without interface modeling. The real stress state can be predicted accurately and the results demonstrate the usefulness of the proposed interface modeling for the strength design of composite laminates.

• Structural Engineering and Mechanics
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• 제25권6호
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• pp.753-765
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• 2007

The response histories and distribution of dynamic interlaminar stresses in composite laminated plates under free vibration and thermal load is studied based on a thermoelastodynamic differential equations. The stacking sequence of the laminated plates may be arbitrary. The temperature change is considered as a linear function of coordinates in planes of each layer. The dynamic mode of displacements is considered as triangle series. The in-plane stresses are calculated by using geometric equations and generalized Hooke's law. The interlaminar stresses are evaluated by integrating the 3-D equations of equilibrium, and utilizing given boundary conditions and continuity conditions of stresses between layers. The response histories and distribution of interlaminar stress under thermal load are presented for various vibration modes and stacking sequence. The theoretical analyses and results are of certain significance in practical engineering application.

• 한국해양공학회지
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• 제9권2호
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• pp.89-97
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• 1995

The investigate the effect of fiber orientation on the interlaminar fracture toughness of carbon fiber reinforced plastics three prepregs which are domestic products are used in this paper. Those are used for the unidirectional composites, but only one is used for the cross-ply laminate composites which is molded $[0/90]_{6s},\;[0/45]_{6s},\;and\;[0/45/90]_{4s}$. The specimens used for the mode I and mode II Tests are DCB and ENF samples are examined by scanning electron microscope(SEM). The value of $G_{IC}$ is almost same when modified three calculating methods are applied. The highest value of $G_{IC}$at crack initiation is obtained at the $[0/90]_{6s}$ interlaminar and the lowest one is at the $[0/45/90]_{4s}$ interlaminar. The highest value of $G_{IIC}$ at crack initiation, however, is obtained at the $[0/90]_{6s}$ interlaminar and the lowest one is at the $[0/45]_{6s}$. The photographs of SEM show a difference behaviour between mode I and mode II fracture surface.

• 한국결정학회지
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• 제13권2호
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• pp.69-72
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• 2002

본 연구에서는 적층판 자유단 근처에서의 층간응력 문제를 해석하였다. 탄소섬유 복합적층판 [+40/-40］s과 탄소 부직포가 삽입된 적층판 ［+40//-40］s 이 인장하중을 받고 있는 경우에 대하여 해석한다. 부호 “//”는 층간에 부직포가 위치함을 의미한다. 부직포를 삽입함으로서 모우드 Ⅱ의 층간파괴인성치는 크게 증가하지만 모우드 I의 값은 크게 변하지 않음이 보고되어 있다./sup 3)/ 복합재료 구조물에 있어서 모우드 Ⅲ 층간파괴인성치가 중요하지만 그 값을 실험적으로 평가하기는 어렵다. 따라서, 본 연구에서는 부직포 효과 특히, 적층판 자유단 근처에서의 모우드 Ⅲ층간파괴 특성을 이해하기 위하여 유한요소 해석을 통해 전단응력을 분석하고자 한다.

• 한국철도학회논문집
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• 제8권6호
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• pp.573-580
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• 2005

Model I interlaminar fracture behaviors of the carbon/epoxy composite, one of the candidate composites for a tilting train carbody, were investigate by the use of DCB(Double cantilever beam) specimens. These specimens were made of CF3327 plain woven fabric with epoxy resin, and an artificial starter delamination was fabricated by inserting Teflon film with the thickness of $12.5{\mu}m$ of $25.0{\mu}m$ at the one end of the specimen. Mode I interlaminar fracture toughness was evaluated for the specimens with the different thickness of an inserter. Also delamination propagating behaviors and interlaminar fracture surface were examined through an ooptical travelling scope and a scanning electron microscope. We found that abruptly unstable crack propagation called as stick-slip phenomena was observed. In addition, interlaminar fracture behaviors were affected on the location and the morphology of a crack tip as well as an interface region.

• Composites Research
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• 제30권1호
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• pp.71-76
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• 2017

본 연구에서는 환경인자에 노출된 탄소섬유/에폭시 복합재의 층간전단강도를 이용하여 장기 성능을 예측하였다. 필라멘트와인딩 공법으로 제작된 층간전단시편은 분위기 온도가 $50^{\circ}C$, $70^{\circ}C$, $100^{\circ}C$인 건조 조건과 분위기 온도가 $25^{\circ}C$, $50^{\circ}C$, $70^{\circ}C$인 침수 조건에 각각 3000시간까지 노출시켰다. 연구결과에 따르면 분위기 온도가 $50^{\circ}C$와 $70^{\circ}C$인 건조 상태에서는 층간전단강도가 노출시간에 따라 크게 변하지 않지만 분위기 온도가 $100^{\circ}C$인 건조 상태에서는 노출시간이 길어지면 후경화로 인해 다소 증가한다. 그러나 분위기 온도가 $25^{\circ}C$인 침수 상태의 경우 층간전단강도는 노출 초기에 크게 변하지 않다가 노출시간이 길어지면 감소하고 감소 정도는 분위기 온도가 높아지면 커진다. 각 분위기 온도에 대한 층간전단강도 선형회귀식은 침수 상태에 3000시간까지 노출된 시편에서 얻은 층간전단강도에서 구할 수 있었다. 이들 선형 회귀식을 이용하면 층간전단강도는 분위기 온도가 $25^{\circ}C$와 $50^{\circ}C$인 경우 측정값의 5.5% 이내, 분위기 온도가 $70^{\circ}C$인 경우 측정값의 2.3% 이내로 예측이 가능하였다. 따라서 제시된 성능 예측 절차는 환경인자에 노출된 탄소섬유/에폭시 복합재의 장기 층간전단강도를 잘 예측할 수 있다.

• The Korean Journal of Pain
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• 제28권1호
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• pp.11-21
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• 2015

Background: Epidural injections are performed utilizing 3 approaches in the lumbar spine: caudal, interlaminar, and transforaminal. The literature on the efficacy of epidural injections has been sporadic. There are few high-quality randomized trials performed under fluoroscopy in managing disc herniation that have a long-term follow-up and appropriate outcome parameters. There is also a lack of literature comparing the efficacy of these 3 approaches. Methods: This manuscript analyzes data from 3 randomized controlled trials that assessed a total of 360 patients with lumbar disc herniation. There were 120 patients per trial either receiving local anesthetic alone (60 patients) or local anesthetic with steroids (60 patients). Results: Analysis showed similar efficacy for caudal, interlaminar, and transforaminal approaches in managing chronic pain and disability from disc herniation. The analysis of caudal epidural injections showed the potential superiority of steroids compared with local anesthetic alone a 2-year follow-up, based on the average relief per procedure. In the interlaminar group, results were somewhat superior for pain relief in the steroid group at 6 months and functional status at 12 months. Interlaminar epidurals provided improvement in a significantly higher proportion of patients. The proportion of patients nonresponsive to initial injections was also lower in the group for local anesthetic with steroid in the interlaminar trial. Conclusions: The results of this assessment show significant improvement in patients suffering from chronic lumbar disc herniation with 3 lumbar epidural approaches with local anesthetic alone, or using steroids with long-term follow-up of up to 2 years, in a contemporary interventional pain management setting.

• Composites Research
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• 제26권2호
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• pp.141-145
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• 2013

본 연구에서는 CFRP 적층판에 다양한 종류의 부직포를 삽입하여 모드 II 층간파괴인성을 평가하고, 파단면의 SEM 분석을 통해 층간파괴인성의 증가 원인을 파악하였다. 모드 II 층간파괴인성값($J/m^2$)은 ENF실험에 의하여 얻어졌으며, 부직포를 삽입하지 않은 시편과 3종류의 부직포(8 $g/m^2$의 탄소부직포, 10 $g/m^2$의 유리부직포, 8 $g/m^2$의 폴리에스테르부직포)가 각각 삽입된 시험편들이 준비되었다. 각 시험편들에 대한 모드 II 층간파괴인성값은 부직포를 삽입하지 않은 시편을 기준으로 탄소부직포를 삽입한 시편은 197.7% 증가하였고, 유리부직포를 삽입한 시편은 약 135.4% 증가하였으며, 폴리에스테르부직포를 삽입한 시편은 약 158.7% 증가하였다. 부직포 삽입에 의한 모드 II 층간파괴인성값의 증가 원인은 SEM 분석에 의한 결과 단섬유의 섬유가교(Fiber bridging), 섬유파단(Fiber breakage), 헥클(Hackle) 등의 발생에 기인된 것으로 확인되었다.

• Composites Research
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• 제28권3호
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• pp.136-141
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• 2015

The stitching process has been widely utilized for the improvement of through-thickness property of the conventional laminated composites. This paper reports the effects of stitching on the flexural and interlaminar shear properties of multi-axial warp knitted (MWK) composites in order to identify the mechanical property improvements. In order to minimize the geometric uncertainties associated with the stacking pattern of fabrics, the regular lay-up was considered in the examination of the stitching effect. The key parameters are as follows: the stitch spacings, the stitching types, the stitching location, and the location of compression fixture nose. These parameters have little effect on the flexural and interlaminar shear properties, except for the case of stitching location. However, the geometry variations caused by the stitching resulted in minor changes to the mechanical properties consistently. Stitching on the $0^{\circ}$ fibers showed the lowest flexural strength and modulus (12% reduction for both properties). The stitch spacing of 5 mm resulted in 8% reduction for the case of interlaminar strength compared with that of 10 mm spacing.

• 대한기계학회논문집
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• 제19권2호
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• pp.391-401
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• 1995

Several tests of the Double Cantilever Beam(DCB) were carried out for influence of the fiber orientation on the Mode I of the interlaminar fracture behavior in the Carbon/Epoxy composites. The interlaminar fracture toughness of Mode I was estimated based on the energy release rate of Mode I, $G_{I}$. The fracture toughness at crack initiation, $G_{IC}$, increases from type A to type E. The fracture toughness, $G_{IR}$ , is almost constant macroscopically for type A and type E when crack propagates. $G_{IR}$ for types B, C, D increases rapidly at the beginning of the crack growth then it decreases gradually. The fracture surface observation by SEM was also obtained the same results. Consequently the influence of the fiber orientation on the Mode I Interlaminar fracture behavior was made clear.ear.