• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.136.1-136.1
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• 2005

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
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• pp.17-21
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• 2002

A finite element method based on the two-dimensional progressive failure analysis is presented for characterizing the strength and failure of the unidirectional-fabric hybrid laminated composite joints under pin loading. The 8-node laminated shell element is incorporated in the updated Lagrangian formulation. Various failure criteria including the maximum stress, Tsai-Wu, Yamada-Sun, and combinations of them are used in conjunction with the complete unloading stiffness degradation method. For the verification, joint tests are conducted for the specimens with various geometries. Although there are some differences depending on the geometry, the finite element model using the Yamada-Sun or the combined Yamada-Sun and Tsai-Wu criterion predicts the failure strength best.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 추계학술발표대회 논문집
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• pp.183-186
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• 2003

Long shafts for power transmission should transmit torsional load with vibrational stability. Hybrid shafts made of unidirectional fiber-reinforced composite and metal have high fundamental bending natural frequency as well as high torque transmission capability. However, thermal residual stresses due to the coefficient difference of thermal expansion of the composite and metal are developed so that the high residual stresses decrease fatigue resistance of the hybrid shafts, especially at low operating temperatures. In this work, axial compressive preload was given to the shaft in order to change the residual stresses. Static and fatigue torsional tests were performed and correlated with stress analyses with respect to the preload and service temperature.

• Composites Research
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• 제29권6호
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• pp.342-346
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• 2016

경량화 소재 중 CFRP(Carbon Fiber Reinforced Plastic)는 카본 섬유를 이용한 섬유구조물이다. 카본과 플라스틱의 특성을 갖는 복합소재이다. 섬유구조는 섬유방향으로 큰 강도를 갖는다. 이러한 경량 소재인 CFRP로 가장 많이 사용되는 것은 직조된 CFRP이다. 직조된 CFRP는 단방향 CFRP에 비하여 구조가 안정적이기 때문이다. 단직조된 CFRP는 고가이다. 따라서 본 연구는 단방향 CFRP의 섬유 구조 특성을 파악하고자 하였다. 본 연구에서는 적층각도 [0/X/-X/0]로 X를 변수로 갖는다. X의 각도 위상이 반전되어 적층된 단방향 CFRP이다. 이러한 단방향 CFRP를 이용하여 중앙 크랙을 갖는 두께 2 mm 판재 형태의 해석 모델을 이용하였다. 해석에서는 핀으로 연결된 상부와 하부에서 하중이 가해지고 있으며 중앙 크랙부분에서 파단을 연구한다. 해석 모델은 CATIA를 이용한 3D Surface 모델로 설계하였다. CFRP 적층을 위해, ANSYS프로그램에서 ACP를 이용한 적층 방향을 결정하여 2개의 적층들을 갖는 해석 모델을 만들었다. 이후 구조해석을 진행하였다.

• 한국안전학회지
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• 제20권2호
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• pp.26-31
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• 2005

The strong continuous fiber reinforced metal matrix composites (MMCs) are recently used in aerospace and transportation applications as an advanced material due to its high strength and light weight. Unidirectional fiber-metal matrix composites have superior mechanical properties along the longitudinal direction. However, the applicability of continuous fiber reinforced MMCs is somewhat limited due to their relatively poor transverse properties. Therefore, the transverse properties of MMCs are significantly influenced by the properties of the fiber/matrix interface. In order to be able to utilize these MMCs effectively and with safety, it must be determined their elastic plastic behaviors at the interface. In this study, the interfacial stress states of transversely loaded unidirectional fiber reinforced metal matrix composites investigated by using elastic-plastic finite element analysis. Different fiber volume fractions $(5-60\%)$ were studied numerically. The interlace was treated as three thin layer (with different properties) with a finite thickness between the fiber and the matrix. The fiber is modeled as transversely isotropic linear-elastic, and the matrix as isotropic elastic-plastic material. Using proposed model, the effects of the interface region and fiber arrangement in MMCs on the distributions of stress and strain are evaluated. The stress distributions of a thin multi layer interface have much less changes compared with conventional perfect interface. The analyses were based on a two-dimensional generalized plane strain model of a cross-section of an unidirectional composite by the ANSYS finite element analysis code.

• 한국세라믹학회지
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• 제51권1호
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• pp.19-24
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• 2014

Three-layer porous alumina-mullite composites with a symmetric gradient porosity are prepared using a controlled freeze/gel-casting method. In this work, tertiary-butyl alcohol (TBA) and coal fly ash with an appropriate addition of $Al_2O_3$ were used as the freezing vehicle and the starting material, respectively. When sintered at $1300-1500^{\circ}C$, unidirectional macro-pore channels aligned regularly along the growth direction of solid TBA were developed. Simultaneously, the pore channels were surrounded by less porous structured walls. A high degree of solid loading resulted in low porosity and a small pore size, leading to higher compressive strength. The sintered porous layered composite exhibited improved compressive strength with a slight decrease in its porosity. After sintering at $1500^{\circ}C$, the layered composite consisting of outer layers with a 50 wt% solid loading showed the highest compressive strength ($90.8{\pm}3.7MPa$) with porosity of approximately 26.4%.

• 대한기계학회논문집A
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• 제30권3호
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• pp.260-268
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• 2006

The micromechanical approach was used to investigate the interfacial strain distributions of a unidirectional composite under transverse loading in which fibers were usually found to be randomly packed. Representative volume elements (RVE) for the analysis were composed of both regular fiber arrays such as a square array and a hexagonal array, and a random fiber array. The finite element analysis was performed to analyze the normal, tangential and shear strains at the interface. Due to the periodic characteristics of the strain distributions at the interface, the Fourier series approximation with proper coefficients was utilized to evaluate the strain distributions at the interface for the regular and random fiber arrays with respect to fiber volume fractions. From the analysis, it was found that the random arrangement of fibers had a significant influence on the strain distribution at the interface, and the strain distribution in the regular fiber arrays was one of special cases of that in the random fiber array.

• 비파괴검사학회지
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• 제21권3호
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• pp.269-276
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• 2001

복합재료의 초음파검사는 매직의 탄성이방성으로 인해 빔스큐(beam skew)현상 등이 발생하기 때문에 등방성 재료의 검사에 비해 훨씬 어렵다. 그 동안의 많은 연구의 결과로서 이방성 재료 네 탄성파의 전파 현상에 대한 해석해법이 정립되어 있으나, 그 해석해가 매우 복잡하여 실제 문제의 해를 구하기 위해서는 수치적인 방법에 의존하여야 하는 경우가 많다. 본 연구에서는 횡등방 이방성(transversely isotropic)으로 가정할 수 있는 단일방향 섬유 복합재료 내 점원에 의한 초음파 전파의 해석해를 먼저 구하고, 이러한 복합재료를 질량-스프링 모델로 모델링하여 해석해에 상응하는 수치해를 구하였다. 그 결과, 초음파의 전파에 대한 수치해와 해석해가 매우 잘 일치하는 것을 확인하였다. 동일한 수치해석법을 사용하여 초음파가 복합재료의 자유표면에서 반사되는 현상과 균일에 의해 산란되는 현상에 대한 수치해도 구하였으며 그 결과를 파동역학의 관점에서 고찰하였다. 본 연구에서 그 유효성이 확인된 수치 모델은 복합재료의 초음파검사를 시뮬레이션 함에 있어 매우 유용하게 사용될 수 있을 것이다.

• Computers and Concrete
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• 제30권5호
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• pp.311-321
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• 2022

The interfacial bond strength of partially encased composite (PEC) structure tends to 0, therefore, the cast-in-place concrete theoretically cannot embody better composite effect than the fabricated structure. A total of 12 specimens were designed and experimented to investigate the energy dissipation and damage of fabricated PEC beam through unidirectional cyclic loading test. Because the concrete on both sides of the web was relatively independent, some specimens showed obvious asymmetric concrete damage, which led to specimens bearing torsion effect at the later stage of loading. Based on the concept of the ideal elastoplastic model of uniaxial tensile steel and the principle of equivalent energy dissipation, the energy dissipation ductility coefficient is proposed, which can simultaneously reflect the deformability and bearing capacity. In view of the whole deformation of the beam, the calculation formula of energy dissipation is put forward, and the energy dissipation and its proportion of shear-bending region and pure bending region are calculated respectively. The energy dissipation efficiency of the pure bending region is significantly higher than that of the shear-bending region. The setting of the screw arbors is conducive to improving the energy dissipation capacity of the specimens. Under the condition of setting the screw arbors and meeting the reasonable shear span ratio, reducing the concrete pouring thickness can lighten the deadweight of the component and improve the comprehensive benefit, and will not have an adverse impact on the energy dissipation capacity of the beam. A damage model is proposed to quantify the damage changes of PEC beams under cyclic load, which can accurately reflect the load damage and deformation damage.

• 대한기계학회논문집A
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• 제22권3호
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• pp.540-544
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• 1998

Compliance calibration method is frequently used to determine $G_IC$ from the DCB composite specimen. However, the method requires at least 4 to 5 fracture test (loading-unloading) records. In this study, $G_IC$ of unidirectional graphite/epoxy DCB composites was determined from the elastic work factor approach which uses a single fracture test record. In order to inspect the validity of the elastic work factor approach, $G_IC$ determined from the elastic work factor approach was compared to that of determined from the compliance calibration method. It was shown that $G_IC$ determined from the elastic work factor approach was comparable to that determined from the compliance calibration method. That is, the elastic work factor approach can be used to determine $G_IC$ of unidirectional graphite/epoxy DCB specimen from a single fracture record.