• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.169-172
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• 2008

FPR(Fiber Reinforced Polymer)는 중량에 비해 높은 강도, 높은 내부식성 등 우수한 역학적 특성으로 인해 최근 건설분야에 적용되는 사례가 많아지고 있으며, 특히 콘크리트 구조물 보강에 가장 활발히 적용되고 있다. FRP를 이용한 전통적인 보강방법은 인장면에 FRP를 부착하는 부착공법이었으나, 부착공법은 FRP의 박리 또는 부착파괴와 같은 조기파괴 문제점과 고정하중과 분담과 사용성 개선이 어려운 단점을 갖고 있다. 이러한 FRP 부착공법의 문제점들을 해결하기 위한 노력으로 최근에는 CFRP 판에 프리스트레스를 도입하는 공법에 대한 연구들이 시작되었다. 판형태의 CFRP를 이용하여 구조물에 긴장력을 도입하면 주인장철근의 응력을 경감시킬 수 있을 뿐만 아니라, 구조물의 균열폭과 휨변형도 감소시킬 수 있으며, 추가되는 활하중뿐만 아니라 고정하중도 일부 분담할 수 있게 되어 고가의 CFRP를 효율적으로 활용할 수 있는 방법이 된다. CFRP 판 긴장공법을 위해 최우선적으로 해결되어야 하는 것은 CFRP 긴장재를 정착하기 위한 적절한 정착장치의 개발이다. 본 연구에서는 CFRP 판 긴장재를 위한 정착장치를 개발하고자 CFRP 판의 정착단부 상세를 변수로 한 정착장치 인장실험을 수행하였으며, 기존 상용 정착구와 비교하여 저비용으로 제작 가능한 CFRP 판 긴장재용 몰드형 정착구의 성능을 검증하였다. 몰드형 정착장치에 대한 성능실험 결과 CFRP 판 긴장재의 표면이 거칠게 처리된 시편이 가장 정착성능이 우수한 것으로 나타났으며, 정착단부의 형상변화는 정착성능에 기여하지 못하는 것으로 나타났다.

• 대한금속재료학회지
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• 제50권9호
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• pp.697-702
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• 2012

In this study, unidirectional and plain woven carbon fiber reinforced magnesium matrix composite laminates were fabricated by the liquid pressing infiltration process, and evolutions of the microstructure and compressive strength of the composite laminates under corrosion were investigated by static immersion tests. In the case of the unidirectional composite laminate, the main microstructural damage during immersion appeared as a form of corrosion induced cracks, which were formed at both CF/Mg interfaces and the interfaces between layers. On the otherhand, wrap/fill interface cracks were mainly formed in the plain woven composite laminate, without any cracks at the CF/Mg interface. The formation of these cracks was considered to be associated with internal thermal residual stress, which was generated during cooling after the fabrication process of these materials. As a consequence of the corrosion induced cracks, the thickness of both laminates increased in directions vertical to the fibers with increasing immersion time. With increasing immersion time, the compressive strengths of both composite laminates also decreased continuously. It was found that the plain woven composite laminates have superior corrosion resistance and stability under a corrosive condition than unidirectional laminates.

• Composites Research
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• 제19권4호
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• pp.1-6
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• 2006

PSF/AS4 복합재 적층구조의 가속노화가 피로강도에 미치는 영향을 변분이론을 이용한 에너지 발산율(energy release rate) 분석을 이용하여 연구하였다. 변분이론 분석은 수지미소균열에 대한 파괴역학을 해석하는데 사용되어 왔으며 이 논문에서는 피로하중 하에서 가속노화 시간에 따르는 파괴인성이 어떻게 변하는가를 설명하였다. 수정된 Paris 법칙에 의한 선도는 각 재료마다. 미소균열이 형성되는 특성을 나타낸다. PSF/AS4 $[0/902]_s$ 적층구조가 60일 동안 유리천이온도에 근거를 두고 세분한 4개의 각기 다른 온도로 가속노화를 하였다. 모든 온도에서 파괴인성은 가속노화 시간에 따라 감소하였다. 높은 온도에서의 파괴인성의 감소는 낮은 온도에서의 감소보다 빠르게 진전되었다. 가속노화가 피로강도에 미치는 영향을 파악하기 위해 유리 천이온도인 섭씨 180도에 가까운 170도에서 60일 동안 노화한 것과 노화하지 않은 것을 비교하였다. 노화된 시편에 대하여 파괴인성의 변화(${\Delta}G_m$)가 낮은 값에서 미소균열이 형성되는 것을 알 수 있었다.

• 대한기계학회논문집A
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• 제26권3호
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• pp.553-559
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• 2002

Carbon-fiber which has very small radial dimension makes us difficult to measure it's properties. So in this paper, we suggest a simple method to measure the thermal conductivity of a carbon-fiber's and carbon-fiber-reinforced-plastics(CFRP) laminates. The thermal conductivity of CFRP laminates was measured experimentally at the same time analytically. The experimental model is based on the one-dimensional analysis of fin sample because CFRP laminates has a thin geometric configuration. The analytical model to measure the thermal conductivity of carbon-fiber is expressed by use of mean-field model which is based on Eshelby's elliptical inclusion problem. Therefore the thermal conductivity of angle-ply laminates can be computed by use of effective longitudinal and transverse thermal conductivities of unidirectional composite of the constituents.

• 한국자동차공학회논문집
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• 제8권6호
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• pp.247-258
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• 2000

It is thought that impact damages and hygrothermals can affect to CFRP (Carbon-fiber reinforced plastic) composite laminated due to the sensitivity on the composite laminated Therefore, this paper focuses on the fracture mechanisms experimentally based on a scanning acoustic microscope (SAM) when subjected to impact damages, i.e., foreign object damages(FOD), and also the influence of impact damages and hygrothermals on residual fatigue bending strength of CFRP laminates. Composite laminates used in the experiment are CF/EPOXY orthotropy laminated plates, which constist of two-interfaces [04/904]s. A steel ball launched by an air gun collides against CFRP laminates to generate impact damages. Bending fatigue tests are periodically interrupted for a nondestructive evaluation (NDE) measurement of the progrossive damages to built the fracture mechanism by impact damages, and three-point fatigue bending tests are carried out to investigate the influence of hygrothermals on the effect on the residual bending fatigue strength of CFRP laminates.

• 복합신소재구조학회 논문집
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• 제1권1호
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• pp.9-15
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• 2010

In this paper, A reinforced concrete slab bridges is analyzed by the composite laminates theory. Both the geometry and the material of the cross section of the reinforced concrete slab bridge are considered symmetrical with respect to the mid-surface so that the bending extension coupling stiffness, Bij = 0, and D16 = D26 = 0. Each longitudinal and transverse steel layer is regarded as a lamina, and material constants of each lamina is calculated by the use of rule of mixture. This slab with simple support is under uniformly distributed vertical and axial loads. In this paper, the finite difference method and specially orthotropic laminates theory are used for analysis. The result of specially orthotropic laminates theory analysis is modified to obtain the solution of the beam analysis. The result of this paper can be used for reinforced concrete slab analysis by the engineers with undergraduate study in near future.

• International Journal of Aeronautical and Space Sciences
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• 제18권2호
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• pp.236-244
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• 2017

In this study, the high-velocity impact penetration behavior of $[45/0/-45/90]_{ns}$ carbon/epoxy composite laminates was studied. The considered configuration includes a spherical steel ball impacting clamped circular laminates with various thicknesses and diameters. First, the impact experiment was performed to measure residual velocity and extent of damage. Next, the impact experiment was numerically simulated through finite element analysis using LS-dyna. Three-dimensional solid elements were used to model each ply of the laminates discretely, and progressive material failure was modeled using MAT162. The result indicated that the finite element simulation yielded residual velocities and damage modes well-matched with those obtained from the experiment. It was found that fiber damage was localized near the impactor penetration path, while matrix and delamination damage were much more spread out with the damage mode showing a dependency on the orientation angles and ply locations. The ballistic-limit velocities obtained by fitting the residual velocities increased almost linearly versus the laminate diameter, but the amount of increase was small, showing that the impact energy was absorbed mostly by the localized impact damage and that the influence of the laminate size was not significant at high-velocity impact.

• Structural Engineering and Mechanics
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• 제64권6권
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• pp.783-792
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• 2017

Carbon Fiber Reinforced Polymer (CFRP) laminates are used widely either for repairing or strengthening of existing structures. When CFRP laminates are used for strengthening of RC continuous T-beams in the Hogging Moment Zone (HMZ); above and around the intermediate supports, it is important to study the expected positions of the laminates across the width of the beam flange. Although, it is traditional to consider CFRP laminates added above the beam web, this is not practical since walls and columns are located in such positions in general. This paper examines the effect of changing the positions of CFRP laminates used for the strengthening of the hogging moment zone across the beam flange of two-span-T-section beams. The Finite Element (FE) Package ANSYS is used to create 3-D theoretical models needed for the study. It can be concluded that changing the position of CFRP strengthening across the beam flange, in the hogging moment zone, is effective upon the overall behavior. The best locations are either above the web or at the flange just beside the web, due to the presence of walls and/or columns.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.784-789
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• 2001

In order to investigate the fracture behaviors(penetration modes) and the resistance to penetration during ballistic impact of cold-rolled Al 5052 H34 alloy laminates, anodized Al 5052 H34 alloy laminates, and Al 5052 H34 alloy after cold-rolling, ballistic testing was conducted. In general, superior armor material is brittle materials which have a high hardness. Ballistic resistance of these materials was measured by protection ballistic limit(V50), a statical velocity with 50% probability for incomplete penetration. Fracture behaviors and ballistic tolerance, described by penetration modes, are observed respectfully, resulting from V50 test and Projectile Through Plate(PTP) test at velocities greater than V50. PTP tests were conducted with 0$^{\circ}$obliquity at room temperature using 5.56mm ball projectile. V50 tests with 0$^{\circ}$obliquity at room temperature were also conducted with projectiles that were able to achieve near or complete penetration during PTP tests. Surface Hardness, resistance to penetration, and penetration modes of Al 5052 H34 alloy laminates compared to those of cold-rolled Al 5052 H34 alloy laminates and anodized Al 5052 H34 alloy laminates anodized Al 5052 H34 alloy after cold-rolling.

• Journal of Mechanical Science and Technology
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• 제16권3호
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• pp.292-301
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• 2002

Ultrasound waves interact strongly with the orientation and sequence of the plies in a layup when propagating in the thickness direction of composite laminates. Also the layup orientation greatly influences its properties in a composite laminate. If the layup orientation of a ply is misaligned, it could result in the part being rejected and discarded. Now, most researchers cut a small coupon from the waste edge and use a microscope to optically verify the ply sequences on important parts. This may add a substantial cost to the production since the test is both labor intensive and performed after the part is cured. A nondestructive technique would be very beneficial, which could be used to test the part after curing and requires less time than the optical test. Therefore we have developed, reduced, and implemented a novel ply-by-ply vector decomposition model for composite laminates fabricated from unidirectional plies. This model decomposes the transmission of a linearly polarized ultrasound wave into orthogonal components through each ply of a laminate. High probability is found, by comparisons between the model and tests, in characterizing cured layups of the laminates by using the proposed method.