• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.79-82
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• 2002

A finite element method based on the two-dimensional progressive failure analysis considering material nonlinearity 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. Failure criteria including the Maximum Stress and Tsai-Wu are used in conjunction with the complete unloading stiffness degradation method. For the verification, joint tests are conducted for the specimens with two different ply-number ratios of UD composite to fabric composite. Although there are some differences depending on ply-number ratios, the finite element model using the maximum stress criterion considering nonlinear material behavior predicts the failure strength best.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.110-113
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• 2002

As a preliminary study for the three dimensional failure analysis of composite joints, the three dimensional stress analysis on a pin-loaded unidirectional-fabric hybrid composite joints are performed. The contact and frictions between composite plate and metal bush are considered in the finite element method by NASTRAN. Experiments are conducted to validate the accuracy and feasibility of the finite element technique for 25 specimens with 5 different geometries. The finite element and experimental results show the bush cap induces the unsymmetric deformation, stress distribution, and failure behavior through the thickness. The experiment also shows the failure loads are higher in the joint with bush cap than without it.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.3
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• pp.579-587
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• 1998

In this study, fatigue behavior of the optical fiber sensor embedded in composite laminate was investigated. Static tensile and fatigue tests were performed for three types of laminated composite specimens with embedded optical fiber sensor in the neutral plane ; [0/sub 6//OF/0/sub 6/]/sub T/, [0/sub 2//90/sub 4//OF/90/sub 4//0/sub 2/]/sub T/ and [0/sub 3//90/sub 3//OF/90/sub 3//0/sub 3/]/sub T/. The fracture of the embedded optical fiber sensor was detected by the intensity drop off of laser signal transmitted through the optical fiber sensors embedded within laminated composite specimen. The maximum fatigue stress applied to laminated specimen was compared with the average tensile stress at which the fracture of the embedded optical fiber within the laminate occurred under static tensile loading. From the experiments, firstly it is observed that the decrease in the life of optical fiber sensors embedded within unidirectional-ply laminate by the fatigue loading is relatively small compared to that of cross-ply laminate. Secondly, the optical fiber embedded in unidirectional-ply laminate is fractured by the fatigue damage due to the growth of internal defects of optical fiber, however the optical fiber embedded in cross-ply laminate is fractured by the growth of transverse matrix crack.

• Composites Research
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• v.29 no.6
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• pp.321-327
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• 2016

In this study, tests and finite element analyses were performed regarding compression after impact strength for laminated composite structures of unidirectional carbon fiber reinforced plastic widely used in structural materials. Two lay-up sequences of composite laminates were selected as test specimens and four impact energy conditions were applied respectively. Impact and compressive strength tests were conducted in accordance with ASTM standards. Impact damages in test specimens were analyzed by using non-destructive inspection method of C-Scan, and compression after impact strengths were calculated with compressive test results. Progressive failure analysis method that can progressively simulate damages and fractures of fiber/matrix/lamina/laminate level was used for impact and compressive strength analyses. All analysis results including contact force, deflection, impact damages, compressive strengths, etc. were compared to test results, and the validity of analysis method was verified.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.611-617
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• 1991

Effective stiffness of short fiber composite with a three-dimensional random orientation of fibers is derived theoretically and compared with available experimental data. The laminate analogy and transformed laminate analogy are used for modulus prediction of 2-D and 3-D random composites, respectively. The effective stiffness of random oriented fiber composite can be expressed in terms of longitudinal and transverse stiffnesses of unidirectional composites. The result of transformed laminate analogy is more accurate than other approaches such as, Christensen-Waals equational and Lavengood-Goettler equation, etc. Also the effective properties of random oriented fiber composite can be expressed in terms of fiber and matrix properties such as elastic modulus, shear modulus and Poisson's ratio.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.118-121
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• 2002

Polyvinylidene di-fluoride (PVDF) film sensor appeared to be practically useful for the structural health monitoring of composite materials and structures. PVDF film sensors were either attached to or embedded in the graphite/epoxy composite (CFRP) samples to detect the fatigue damage at the bondline of single-lap joints or the tensile failure of unidirectional laminates. PVDF sensors were sensitive enough to detect and determine the crack front in linear location since composites usually produce very energetic acoustic emission (AE). PVDF sensors are extremely cost-effective, as flexible as other plastic films, in low profile as thin as a few tens of microns, and have relatively wide-band response, all of which characteristics are readily utilized for the structural health monitoring of composite structures. Signals due to fatigue damage showed a characteristics of mode II (shear) type failure whereas those from fiber breakage at DEN notches showed that of mode I (tensile) type fracture.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.12-16
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• 2000

This study is about the effect of braiding on the 2-D biaxial braided hollow composite(BD) compared with unidirectional hollow composite(UD). The specimens were made of T700S Carbon/Epoxy prepreg and T700S dried Carbon yarns. Fiber volume fraction of UD and BD was obtained experimentally and analytically. Fiber volume fraction of BD was derived based on unit cell of braiding yarn section. Bending test was executed to investigate the effect of braiding part. The result of experiment and analysis of fiber volume fraction has good agreement. Bending strength of BD is about 20% higher than that of UD.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1990.11a
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• pp.63-68
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• 1990

Friction and wear behavior of a unidirectional high modulus carbon fiber reinforced epoxy composite exposed to high and low humidity was experimentally examined with various sliding speeds. The results show that the moisture at the sliding surface greatly influences friction and wear properties of the composite. It is also discoverd that the difference in friction and wear behavior between samples with different fiber orientations is mainly due to the anisotropic properties caused by the microstructure of oriented graphite crystals in the carbon fibers and the macrostructure of fiber orientation in the matrix.

• Tribology and Lubricants
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• v.6 no.2
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• pp.88-93
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• 1990

Friction and wear behavior of a unidirectional high modulus carbon fiber reinforced epoxy composite exposed to high and low humidity was experimentally examined with various sliding speeds. The results show that the moisture at the sliding surface greatly influences friction and wear properties of the composite. It is also discoverd that the difference in friction and wear behavior between samples with different fiber orientations is mainly due to the anisotropic properties caused by the microstructure of oriented graphite crystals in the carbon fibers and the macrostructure of fiber orientation in the matrix.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.1
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• pp.37-43
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• 2004