• Composites Research
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• v.12 no.1
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• pp.68-75
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• 1999

This study has observed that the dynamic behavior of Metal Matrix Composites (MMCs) in low velocity impact varies with impact velocity. MMCs with 15 fiber volume percent were fabricated by using the squeeze casting method. The AC8A was used as the matrix, and the alumina and the carbon were used as reinforcements. The tensile and vibration tests conducted yielded the yielded the tensile stress and elastic modulus of MMCs The low pass filter and instrumented impact test machine was adopted to study dynamic behaviors of MMCs corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact energy of unreinforced alloy and MM s increased as the impact velocity increased. The increase of crack propagation energy was especially prominent, but the dynamic toughness of each material did not change much. To show the relation between crack initiation energy and dynamic fracture toughness, a simple model was proposed by using the strain energy and stress distribution at notch. The model revealed that crack initiation energy is proportional to the square of dynamic fracture toughness and inversely proportional to elastic modulus.

• Korean Journal of Materials Research
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• v.4 no.3
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• pp.253-258
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• 1994

The effect of hole size and hole-to-hole distance in the braided and laminated composite was studied in terms of tensile strength, pin bearing strength, and flexural strength of S2-glass fiber braided polyester. The tensile strength reduction with hole size was well fitted with he Whitney and Nuismer's prediction for the laminated composite. The characteristic distance was measured to be about 1.6mm for braided composite and 1.8mm for laminated one. The effect of distance between the centers of two circu lar holes on tensile strength was negligible when the distance between these two holes was larger than 4 times of the diameter of circular hole for both braided and laminated composite. The side effect was diminished when the center of hole was located 3 times farther than the diamet.er of the hole. The pin bearing strengths was decreased with the size of pin hole for both braided and laminated composite.

• Composites Research
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• v.12 no.2
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• pp.10-25
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• 1999

A new evaluation method for the interfacial properties of fibrous composites based on a fragmentation technique is proposed by using the gradual multi-fiber composite, in which the inter-fiber spacing is gradually changed. The results showed that as the inter-fiber distance increased, the aspect ratio of broken fibers decreased while the interfacial shear strength between the fiber and matrix increased. When the reciprocal of the inter-fiber destance was taken for the above relations, both the aspect ratio and interfacial shear strength showed a saturated value. This means that the gradual multi-fiber composite indicates an upper bound in aspect ratio and an upper bound in interfacial shear strength. It was concluded that this fragmentation test could be a new method for composite evaluation, since reducing a difference between these two bounds is effective for composite strengthening. In addition an elastoplastic finite element analysis was carried out to relate the above results with fiber stress a distribution around fiber breaks. It was proved that the bound obtained in the gradual multi-fiber composite test is closely related to stress concentrations caused by a group of multi-fiber breaks.

• Composites Research
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• v.36 no.2
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• pp.101-107
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• 2023

In this study, aluminum nitride (AlN) reinforced aluminum (Al) matrix composites are fabricated via plasma arc melting under a nitrogen atmosphere. Within a minute of the chemical reaction between Al and N, dispersed AlN with the shape of transient and lamellar layers is in situ formed in the Al matrix. The composite contains 10 vol.% AlN reinforcements with low thermal resistance and strong bonding at the interfaces, which leads to the unique combination of thermal expansivity and conductivity in the resulting composites. The coefficient of thermal expansion of the composite can be further reduced when Si was alloyed into the Al matrix, which proposes the potential of the in situ Al matrix composites for thermal management applications.

• Composites Research
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• v.26 no.4
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• pp.235-244
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• 2013

A volume integral equation method (VIEM) is introduced for the solution of elastostatic problems in an unbounded isotropic elastic solid containing multiple isotropic elliptical fibers of arbitrary orientation subject to uniform stress at infinity. The fibers are assumed to be long parallel elliptical cylinders composed of isotropic elastic material perfectly bonded to the isotropic matrix. The solid is assumed to be under plane strain on the plane normal to the cylinders. A detailed analysis of the stress field at the matrix-fiber interface for square and hexagonal packing of the fibers is carried out for different values of the number, orientation angles and concentration of the elliptical fibers. The accuracy and efficiency of the method are examined through comparison with results obtained from analytical and finite element methods.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.45-49
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• 2006

The thermal degradation of carbon fiber reinforced phenolic composites have been studied at high temperature by using thermogravimetry analysis (TGA). The aim is that ultimately it can be used to predict the service temperature during solid rocket firing for any level and type of mechanical loading and to recommend protection systems required. To simulate the high heating rate in firing condition, the modified thermal decomposition constant (1000 K/min) was used for FEM analysis. The temperature distribution and the thickness of thermal decomposition were estimated well and we could predict the thickness of thermal decomposition within ${\pm}1mm$.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.22-25
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• 2005

The thermal degradation of carbon/phenolic composite have been studied at high temperature by using thermogravimetric (TGA). A heating .ate of 5, 10, 15, 30 and $50^{\circ}C/min$ was used for the determination of thermal decomposition parameters of composite materials at high-temperature service. It has been shown that as the heating rates is increased, the peak decomposition rates are occur at higher temperature. Based on results of thermogravimetric analysis, the pyrolysis process is analyzed and physical and mathematical models for the process are proposed. The thermal analysis also has been conducted using transient heat conduction and the in-depth temperature distribution and the density profile were evaluated along the solid rocket nozzle. As a future effort the thermal decomposition parameter determined in this investigation will be used as input to thermal and mechanical analysis when subjected to solid rocket propulsion environment.

• Composites Research
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• v.23 no.4
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• pp.7-13
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• 2010

A volume integral equation method (VIEM) is introduced for the solution of elastostatic problems in an unbounded isotropic elastic solids containing interacting multiple anisotropic inclusions subject to remote uniaxial tension. The method is applied to two-dimensional problems involving long parallel cylindrical inclusions. A detailed analysis of stress field at the interface between the matrix and the central inclusion is carried out for square and hexagonal packing of the inclusions. Effects of the number of anisotropic inclusions and various fiber volume fractions on the stress field at the interface between the matrix and the central inclusion are also investigated in detail. The accuracy of the method is validated by solving the single inclusion problem for which solutions are available in the literature.

• The Journal of the Acoustical Society of Korea
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• v.11 no.4
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• pp.22-30
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• 1992

The propagation of coherent time-harmonic elastic SH waves in a medium with random distribution of cylindrical inclusions is studied for characterizing the dynamic elastic modulus and the attenuation property of fiber-reinforced composite materials. A multiple scattering theory using the single scattering coefficients in conjunction with the Lax's quasicrystalline approximation is derived and from which the dispersion relation for such medium is obtained. The pair-correlation functions between the cylinders which are needed to formulate the multiple scattering interaction between the cylinders are obtained by Monte Carlo simulation method.From the numerically calculated complex wavenumbers, the propagation speed of the average wave, the coherent attenuation coefficient and the effective shear modulus are presented as functions of frequency and area density.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.6
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• pp.34-44
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• 1996

In order to examine the accuracy of the intensity method, the fiber orientation-angle distribution of fiber-reinforced polymeric composites is measured using image processing. The fiber orientation function is calculated from the fiber orientation measured by the soft X-ray photograph. Theoretical and experimental results of fiber orientation function are compared for the composites with different fiber contents and fiber orientations. The intensity method is used for the experimental investigation and the measured fiber orientation function is compared to the calculated one. The relations between the measured and the simulated fiber orientation functions $J{\small{M}}$ and $J{\small{S}}$ respectively are identified. For the fiber length of 1.000mm and 2.000mm, it shows that $J{\small{M}}=0.83J{\small{M}}$. However. in general. the value of $J{\small{M}}$ decreases as the fiber length increases. For GFRP composites the relations between $J{\small{M}}$ and theoretical value J show that $J{\small{M}}$=0.73J for short fiber and $J{\small{M}}$=0.81J for long fiber.