• Composites Research
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• v.26 no.4
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• pp.245-253
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• 2013

In this paper, we developed a theoretical model which is able to predict the tensile strength and elastic modulus of hybrid composites reinforced by two types of randomly distributed discontinuous reinforcements. For this, we considered two known models; One is a prediction model based on the assumption that the composite is reinforced by two types of well aligned continuous reinforcements. The other is a statistical model for the composite which is reinforced by only one type of randomly distributed discontinuous reinforcements. In order to evaluate the validity of accuracy of our prediction model, we measured the strength and elastic modulus of polypropylene hybrid composite reinforced by talc and short glass fiber. We found that the present model drastically enhances the accuracy of strength prediction compared to an existing model, and predicts the elastic modulus within the same order with experimentally measured values.

• Textile Coloration and Finishing
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• v.7 no.4
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• pp.25-32
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• 1995

This study was carried out to examine the influences of fatigue and perspiration on the deterioration of chrome leather for shoes. The samples were treated with acidic and alkaline artificial perspirations and applied cyclic tensile stress, and the elastic recovery from fatigue strain, tensile strength and elongation, stiffness etc. by regions and directions were determined. The physical properties generally indicate considerable difference by regions and directions due to the thickness, entangling state, and arrangement direction of fiber buldles within the leather. By the treatment of artificial perspirations, the length, weight, strength, elastic recovery from fatigue of the lether are decreased and the thicknes, elongation, and stiffness are increased; and their extents by the alkaline perspiration are higher than those by the acidic one. The elastic recovery from fatigue of samples are decreased with increasing fatigue cylcle; and indicate regressive relations against the logarithm of the elapsed time, and the means of regression coefficients are 2.73 > 2.55 > 2.22 for samples treated by the acidic perspiration, untreated, and treated by the alkaline perspiration, respectively. The tensile strength is decreased and elogation is increased by fatigue, but the changes are diminished likely due to a rearrangment of fiber bundles with increasing fatigue cycle. And the samples become a little flexible immediately after fatigue; but stiffen again with elastic recovery from fatigue strain, consequently for some cases their stiffness after recovery are rather greater than those before fatigre.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.839-844
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• 1998

The purpose of this study is to analyze the interface debonding failure on RC beams strengthened with carbon fiber sheet(CFS). The behavior of damaged RC beams strengthened with CFS is analytically investigated using both linear elastic fracture mechanics (LEFM) approach and the finite element method. This study includes the investigation of the separation mode by interface fracture of the strengthening materials due to the interfacial shear and normal stresses.

• Proceedings of the Korean Fiber Society Conference
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• 2001.10a
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• pp.355-358
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• 2001

Copolyetheresters are us,ed as an engineering thermoplastic elastomer due to their excellent mechanical properties, thermooxidative stability up to high temperatures and a good resistance against many chemicals. However, fibers made from the copolyetheresters exhibited elastic recovery of about 80-85％ after being stretched 200％, while spandex fibers usually showed 90-95％ recovery. (omitted)

• Structural Engineering and Mechanics
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• v.5 no.6
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• pp.705-713
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• 1997

The residual thermal stresses at the interface corner between the elastic fiber and the viscoelastic matrix of a two-dimensional unidirectional laminate due to cooling from cure temperature down to room temperature were studied. The matrix material was assumed to be thermorheologically simple. The time-domain boundary element method was employed to investigate the nature of stresses on the interface. Numerical results show that very large stress gradients are present at the interface corner and this stress singularity might lead to local yielding or fiber-matrix debonding.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.4
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• pp.63-69
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• 2003

In discontinuous composite mechanics, shear lag theory is one of the most popular model because of its simplicity and accuracy. However, it does not provide sufficiently accurate strengthening predictions in elastic regime then the fiber aspect ratio is small. This is due to its neglect of stress transfer across the fiber ends and the stress concentrations that exist in the matrix regions near the fiber ends. To overcome this shortcoming, a more simplified shear lag model introducing the stress concentration factor which is a function of several variables, such as the modulus ratio, the fiber volume fraction, the fiber aspect ratio, is proposed. It is found that the modulus ratio($E_f$/$E_m$) is the essential variable among them. Thus, the stress concentration factor is expressed as a function of modulus ratio in the derivation. It is found that the proposed model gives a good agreement with finite element results and has the capability to correctly predict the values of interfacial shear stresses and local stress variations in the small fiber aspect ratio regime.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.6 s.237
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• pp.876-888
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• 2005

Tensile properties and fracture toughness of monolithic aluminum, fiber reinforced plastics and glass fiber/aluminum hybrid laminates under tensile loads have been investigated using plain coupon and single-edge-notched specimens. Elastic modulus and ultimate tensile strength of GFMLs showed different characteristic behaviors according to the Al kind, fiber orientation and composition ratio. Fracture, toughness of A-GFML-UD which was determined by the evaluation of $K_{IC}$ and $G_{IC}$ based on critical load was similar to that of GFRP-UD and was much higher than monolithic Al. Therefore, A-GFML-UD presented superior fracture toughness as well as prominent damage tolerance in comparison to its constituent Al. By separating Al sheet from GFMLs after the test, optical microscope observation of fracture zone of GFRP layer in the vicinity of crack tip revealed that crack advance of GFMLs depended on the orientation of fiber layer as well as Al/fiber composition ratio.

• Transactions of Materials Processing
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• v.32 no.1
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• pp.28-34
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• 2023

In this research, a representative volume element (RVE)-based FE Model is presented to estimate the mechanical properties of additively manufactured continuous fiber-reinforced composites with different fiber orientations. To construct the model, an ABAQUS Python script has been implemented to produce matrix and fiber in the desired orientations at the RVE. A script has also been developed to apply the periodic boundary conditions to the RVE. Experimental tests were conducted to validate the numerical models. Tensile specimens with the fiber directions aligned in the 0, 45, and 90 degrees to the loading direction were manufactured using a continuous fiber 3D printer and tensile tests were performed in the three directions. Tensile tests were also simulated using the RVE models. The predicted Young's moduli compared well with the measurements: the Young's modulus prediction accuracy values were 83.73, 97.70, and 92.92 percent for the specimens in the 0, 45, and 90 degrees, respectively. The proposed method with periodic boundary conditions precisely evaluated the elastic properties of additively manufactured continuous fiber-reinforced composites with complex microstructures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1A
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• pp.19-24
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• 2011

Concrete columns strengthening effect due to FRP (Fiber Reinforced Polymer) confinement depends on the elastic modulus of the FRP. This study analyzes the retrofitting effect of FRP confinements according to elastic modulus of FRPs using the existing data and suggests a practical model to assess the strengthening effect. This study subdivides the FRP elastic modulus into three parts based on normal concrete and steel elastic modulus. The slope and the y-axis intersection seem to increase with increasing FRP elastic modulus. In addition, the strengthening effect does not develop up to some amount of FRP confinement having relatively smaller elastic modulus than the compressive elastic modulus of concrete. In this case, a linear model to assess the strengthening effect is hard to be used. Thus, this study suggests that the FRP jackets having 2 times larger elastic modulus than that of concrete are recommended to be used for retrofit of concrete and that a linear model can be applied for the case. The suggested model shows nearly the same result regardless to the restraint of the y-axis intersection. This has been observed at the model of steel confinement and, thus, is a reliable result.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.11
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• pp.694-697
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• 2015

We investigated the characterizations of carbon films fabricated by dual magnetron sputtering under various RF powers for the improvement of physical properties in carbon fiber (CF). All sputtered carbon films exhibited amorphous structure, regardless of RF powers, resulting in uniform and smooth surfaces. The hardness and elastic modulus are increased with the increase of RF power, and the adhesion and friction properties of carbon films were improved with the increase of RF power. In the results, The increase of RF power in the sputtering method improved tribological properties of the carbon films, and these attributes can be expected to improve the physical properties of the carbon fiber reinforcement plastics.