• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.3 s.22
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• pp.124-130
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• 2005

In this paper, the effects of matrix hygrothermal aging and residual stress changes on $Avimid^{(R)}$ K3B/IM7 laminates in $80^{\circ}C$ water were studied. The factors causing the $80^{\circ}C$ water to degradation of the laminates could be the degradation of the matrix toughness, the change in residual stresses. After 500 hours fully saturated aging of the neat resin, the weight gain was 1.55% increase with the diffusion coefficient $7{\times}10^{-6}m^2/s$ and the fracture toughness was decreased about 41%. After 100 hours fully saturated aging of the $[+45/0/-45/90]_s$ K3B/IM7 laminates in $80^{\circ}C$ water, the weight gain was 0.41% increase with the diffusion coefficient $1{\times}10^{-6}m^2/s$ and the loss of the microcracking fracture toughness was 43.8% of the original toughness. To see whether the residual stress influenced the fracture toughness, two ply $[90^{\circ}/0^{\circ}]$ laminates were put in $80^{\circ}C$ water from 2 hours to 8 hours. The changes in residual stress in 8 hours are less than 3MPa. Because the 3MPa change is not sufficient to degrade the laminates, the main factor to degrade the microcracking fracture toughness was the degradation of the matrix fracture toughness.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.38 no.7
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• pp.511-523
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• 1989

This paper investigates physical properties, the electrical and mechanical characteristics of the epoxy resin with different curing methods and postcuring conditions at room temperature or cryogenic temperature (LN2). According to the results in this paper, first, it is found that the physical properties, electrical and mechanical characteristics of the epoxy resin are largely affected by the interior reaction temperature on the curing. Thus, in the fabrication of the sample, several excellent characteristics of the sample are obtained by controlling the interior reaction temperature of the epoxy resin. Second, the sample having optimal electrical and mechanical characteristics is obtained for the repetitive post-curing method at 100c in view point of the post-curing conditions of the epoxy resin. Third, it appears that tan and characteristics at LN2 temperature are about half of those at room temperature. Fourth, it appears that the dielectric strength of the epoxy resin at LN2 temperature is higher by about 0.6-1.0 MV/cm than that at room temperature. The heat-aging of the epoxy resin due to the micro-defect and excess fever-movement have been noticed to affect dielectric strength at LN2 temperature more significantly than at room temperature.

• Restorative Dentistry and Endodontics
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• v.29 no.6
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• pp.520-531
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• 2004

The aim of this study was to investigate the effect of monomer and filler compositions on the rheological properties related to the handling characteristics of resin composites. Methods. Resin matrices that Bis-GMA as base monomer was blended with TEGDMA as diluent at various ratio were mixed with the Barium glass (0.7 um and 1.0 um), 0.04 um fumed silica and 0.5 um round silica. All used fillers were silane treated. In order to vary the viscosity of experimental composites, the type and content of incorporated fillers were changed, Using a rheometer, a steady shear test and a dynamic oscillatory shear test were used to evaluate the viscosity ($\eta$) of resin matrix, and the storage shear modulus (G'), the loss shear modulus (G"), the loss tangent ($tan{\delta}$) and the complex viscosity (${\eta}^*$) ofthe composites as a function of frequency ${\omega}{\;}={\;}0.1-100{\;}rad/s$. To investigate the effect of temperature on the viscosity of composites, a temperature sweep test was also undertaken. Results. Resin matrices were Newtonian fluid regardless of diluent concentration and all experimental composites exhibited pseudoplastic behavior with increasing shear rate. The viscosity of composites was exponentially increased with increasing filler volume%. In the same filler volume, the smaller the fillers were used, the higher the viscosities were. The effect of filler size on the viscosity was increased with increasing filler content. Increasing filler content reduced $tan{\delta}$ by increasing the G' further than the G". The viscosity of composites was decreased exponentially with increasing temperature.

• Journal of Adhesion and Interface
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• v.22 no.2
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• pp.63-68
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• 2021

Unsaturated Polyester Resin (UPR) is in general used as a resin to prepare for composite materials with reinforcing materials such as glass fibers. UPR, a thermosetting resin, is used in industry to prepare for sheet molding compound (SMC) molding prepreg that has excellent productivity and is advantageous for mass production among various molding methods of composite materials. The fiber-reinforced composite material using UPR as a matrix material is light and has the advantage of excellent physical properties, but it is weak against impact and is fragile. Four types of polyurethane were synthesized and added to UPR resin to overcome the shortcomings.

• Fibers and Polymers
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• v.4 no.2
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• pp.77-83
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• 2003

The cell modeling homogenization method to derive the constitutive equation considering the microstructures of the fiber reinforced composites has been previously developed for composites with simple microstructures such as 2D plane composites and 3D rectangular shaped composites. Here, the method has been further extended for 3D circular braided com-posites, utilizing B-spline curves to properly describe the more complex geometry of 3D braided composites. For verification purposes, the method has been applied for orthotropic elastic properties of the 3D circular braided glass fiber reinforced com-posite, in particular for the tensile property. Prepregs of the specimen have been fabricated using the 3D braiding machine through RTM (resin transfer molding) with epoxy as a matrix. Experimentally measured uniaxial tensile properties agreed well with predicted values obtained for two volume fractions.

• Journal of the Korean Ceramic Society
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• v.52 no.4
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• pp.284-289
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• 2015

This study examined carbon layer coating on silicon carbide (SiC) fibers by utilizing solid-state and wet chemistry routes to confer toughness to the fiber-reinforced ceramic matrix composites, as an alternative to the conventional pyrolytic carbon (PyC) interphase layer. Electrophoretic deposition (EPD) of carbon black nanoparticles using both AC and DC current sources, and the vacuum infiltration of phenolic resin followed by pyrolysis were tested. Because of the use of a liquid phase, the vacuum infiltration resulted in more uniform and denser carbon coating than the EPD routes with solid carbon black particles. Thereafter, vacuum infiltration with controlled variation in phenolic resin concentration, as well as the iterations of infiltration steps, was improvised to produce a homogeneous carbon coating having a thickness of several hundred nanometers on the SiC fiber. Conclusively, it was demonstrated that the carbon coating on the SiC fiber could be achieved using a simpler method than the conventional chemical vapor deposition technique.

• Composites Research
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• v.14 no.1
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• pp.30-38
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• 2001

As fiber reinforced composite materials are widely used in aircraft, space structures and robot arms, the on-line cure monitoring during the cure process of the composite materials has become an important research area for the better quality and productivity. In this paper, the dielectric circuit of the Wheatstone bridge type for measuring the dissipation factor during cure of thermsetting resin matrix composite materials was designed and manufactured. Also, the dielectric sensor for the cure monitoring of high temperature cure composites was developed and tested. The residual thermal stresses of the dielectric sensor during high temperature cure were analyzed by the finite element method and its dielectric characteristics at high temperature cure were analyzed by the finite element method and its dielectric characteristics at high temperature were evaluated. The on-line cure monitoring of the BMI(Bismaleimide) resin was performed using the developed Wheatstone bridge type circuit and the high-temperature dielectric sensor.

• International Journal of Concrete Structures and Materials
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• v.10 no.4
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• pp.539-553
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• 2016

Polymer concrete (PC) has been favoured over Portland cement concrete when low permeability, high adhesion, and/or high durability against aggressive environments are required. In this research, a new class of PC incorporating Multi-Walled Carbon Nanotubes (MWCNTs) is introduced. Four PC mixes with different MWCNTs contents were examined. MWCNTs were carefully dispersed in epoxy resin and then mixed with the hardener and aggregate to produce PC. The impact strength of the new PC was investigated by performing low-velocity impact tests. Other mechanical properties of the new PC including compressive, flexural, and shear strengths were also characterized. Moreover, microstructural characterization using scanning electron microscope and Fourier transform infrared spectroscopy of PC incorporating MWCNTs was performed. Impact test results showed that energy absorption of PC with 1.0 wt% MWCNTs by weight of epoxy resin was significantly improved by 36 % compared with conventional PC. Microstructural analysis demonstrated evidence that MWCNTs significantly altered the chemical structure of epoxy matrix. The changes in the microstructure lead to improvements in the impact resistance of PC, which would benefit the design of various PC structural elements.

• Applied Chemistry for Engineering
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• v.17 no.4
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• pp.381-385
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• 2006

We applied a new analyzing technique for the polyurethane acrylate hybrid emulsion sample composed of polyurethane resin and acrylate resin using the phase-lag mapping techniques of atomic force microscopy. For the analysis, we synthesized similarly sized pure polyurethane dispersion and acrylate emulsion particles, which were used for measuring the standard phase-lag intensities for each material. Based on these signal intensity, we could discriminate acryl particle in the polyurethane dispersion matrix with the resolution of a few tens of nanometers. Thus, the techniques show a new possibility in the analysis of the organic two-phase particles, and we believe the techniques are helpful to design organic particles.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.9
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• pp.1334-1340
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• 2017

In this paper, a tie-plate shape is optimized by using the numerical technique to reduce the stray load loss of the tie-plate which is a mechanical structure for assembling and supporting of the transformer core. The eddy current loss of the structure is calculated by an electromagnetic field FEM program and the results are compared with 4 different shapes of tie-plates. Since the thickness of the tie-plate is very thin, and the skin depth is very small, the number of FE elements for 3-D transformer model is too big to solve. So, the surface impedance boundary condition (SIBC) is used to reduce the system matrix size and its computing time. To verify the method a 2.5 MVA 22,900/380V distribution transformer is simulated using one objective function and three design variables with some constraints. The final optimized tie-plate has three slots of 6 mm width and 23 mm gap, and the loss is reduced by 75 %. Consequently, the proposed algorithm seems to be considerably applicable to electric machinery as well as power transformer.