• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.5
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• pp.230-235
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• 2004

In this paper, epoxy elasticity factors were investigated by TMA (Thermomechanical Analysis), DMTA (Dynamic Mechanical Thermal Analysis) and FESEM (Field Emission Scanning Electron Microscope) to improve toughness and reduce brittleness of existing epoxy resin. Dumbbell shaped specimens were made and tested at rates of 0, 20 and 35phr (part per hundred resins). TMA temperatures ranged from -2$0^{\circ}C$ to 20$0^{\circ}C$. Tg (glass transition temperature) of elastic epoxy was measured by thermal analysis. Also investigated were thermal expansion coefficient ($\alpha$), modulus and Tan$\delta$ (loss factor). And we analyzed structure through FESEM, could find elastic-factors of elastic epoxy that is not existing-epoxy. In addition, we measured permittivity and Tan$\delta$ for investigation of the electrical properties of elastic epoxy. Permittivity and Tan$\delta$ depend on elastomer composition. Namely, permittivity and Tan$\delta$ increase according to the elastomer contents. For experimental analysis results, 20phr was considered an excellent specimen.

• Journal of Welding and Joining
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• v.11 no.4
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• pp.91-102
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• 1993

The plasma sprayed $Cr_3C_2$-NiCr coatings are widely used as wear-resistant and corrosion-resistant materials. The mechanical and wear properties of the plasma sprayed $Cr_3C_2$-NiCr coating on steel plate were examined in this study. The pore in the coatings could be classified into two types, the one is the intrinsic pore originated from the spraying powder, the other is the extrinsic pore formed during spraying. During the tensile adhesion test, the fracture occured at the interface of top coating and bond coating. It is though that the compressive residual stress increases with the increase of the top coating thickness. From the wear test, it was found that the wear rate increased with the increase of the sliding velocity regardless of the temperature. It is thought that the fracture toughness reduces with the increase of the sliding velocity at $30^{\circ}C$ and that the adhesion amount increases with the increase of the sliding velocity at $400^{\circ}C$ It is concluded that the wear mechanism at $30^{\circ}C$ is the fracture and pull-out of the carbide particles due to the fatigue on sliding surface, while the wear mechanism at $400^{\circ}C$ is the adhesion of the smeared layer formed during wear process.

• Carbon letters
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• v.19
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• pp.1-11
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• 2016

In efforts to characterize and understand the properties and processing of phenylethynyl-terminated imide (LaRC PETI-5, simply referred to as PETI-5) oligomers and polymers as a high-temperature sizing material for carbon fiber-reinforced polymer matrix composites, PETI-5 imidization and thermal curing behaviors have been extensively investigated based on the phenylethynyl end-group reaction. These studies are reviewed here. In addition, the use of PETI-5 to enhance interfacial adhesion between carbon fibers and a bismaleimide (BMI) matrix, as well as the dynamic mechanical properties of carbon/BMI composites, are discussed. Reports on the thermal expansion behavior of intercalated graphite flake, and the effects of exfoliated graphite nanoplatelets (xGnP) on the properties of PETI-5 matrix composites are also reviewed. The dynamic mechanical and thermal properties and the electrical resistivity of xGnP/PETI-5 composites are characterized. The effect of liquid rubber amine-terminated poly(butadiene-co-acrylonitrile) (ATBN)-coated xGnP particles incorporated into epoxy resin on the toughness of xGnP/epoxy composites is examined in terms of its impact on Izod strength. This paper provides an extensive overview from fundamental studies on PETI-5 and xGnP, as well as applied studies on relevant composite materials.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.137-140
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• 2005

Resin transfer molding (RTM) is one of the most popular processes for producing fiber reinforced polymer composites. In the manufacture of complex thick composite structures, analysis on flow front advancement on the resin impregnating the multi-layered fiber preform is helpful for the optimization of the process. In this study, three-dimensional mold filling simulation of RTM is carried out by using CVFEM (Control Volume Finite Element Method). On the assumption of isothermal flow of Newtonian fluid, Darcy’s law and continuity equation are used as governing equations. Different permeability tensors employed in each layer are obtained by experiments. Numerically predicted flow front is compared with experimental one in order to validate the numerical results. Flow simulations are conducted in the two mold geometries, rectangular plate and hollow cylinder. Permeability tensor of each layer preform in Cartesian coordinate system is transformed to cylinder coordinates system so that the flow within the multi-layered preforms of the hollow cylinder can be calculated exactly. Our emphasis is on the three dimensional flow analysis for circular three-dimensional braided preform, which shows outstanding mechanical properties such as high impact strength and toughness compared with other conventional two-dimensional laminar-structured preforms.

• Composites Research
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• v.24 no.2
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• pp.46-50
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• 2011

This paper describes the state of the art for the development of metallic armor materials which are mainly used as armor plates of the combat vehicles. Several important micro-structural features affecting ballistic properties of the metallic armor are discussed. Optimization of the strength and toughness balance of the metallic armor is necessary for the improvement of the ballistic performance resulting from maximizing the resistance to the penetration of the bullet and also to brittle failure of the plates. Understanding and control of the adiabatic shearing phenomenon developed remarkably during high strain rate deformation is needed to prevent brittle failure of the metallic armor materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.7 s.262
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• pp.756-763
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• 2007

The majority of catastrophic wheel failures are caused by surface opening fatigue cracks either in the wheel tread or wheel flange areas. The inclined cracks at railway wheel tread are initiated and the cracks are caused by wheel damage-spatting after 60,000 km running. Because the failured railway wheel is reprofiled before regular wheel reprofiling, the maintenance cost for the railway wheel is increased. Therefore, it is necessary to analyze the mechanism for initiation of crack. In the present paper, the combined effect on railway wheels of a periodically varying contact pressure and an intermittent thermal braking loading is investigated. To analyze damage cause for railway wheels, the measurements for replication of wheel surface and the effect of braking application in field test are carried out. The result shows that the damages in railway wheel tread are due to combination of thermal loading and ratcheting.

• Design & Manufacturing
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• v.6 no.1
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• pp.39-44
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• 2012

Hot tool steel, in general, has not been used as a material in hot forging. However such a hot tool steel is recently applied to forging materials by recent forging technology. DH32 is known as a kind of hot tool steels, which is developed for characteristics of excellent strength and toughness in high temperature. Feasibility of DH32 to hot forging material has been researched to develop the hot forging technology of a plunger used for a large-sized marine fuel pump. Hot compression experimental works were performed to investigate the hot strain characteristic of DH32 and with the experimental results FE simulations were also conducted for the design of forging processes and preform. It is found out through the hot compression experimental works that DH32 has a hot brittleness at more than $1150^{\circ}C$.

• Journal of the Korean Society for Heat Treatment
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• v.6 no.2
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• pp.59-69
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• 1993

Bending fracture strength test and impact strength test were made for VC coated die steels treated by immersing in molten borax bath and for hardened steels which were quenched and tempered, in order to clarify the effect of VC coating at $1000^{\circ}C$. The material used in this investigation was representative cold and hot work die steels STD11, STD61. The results obtained are as follows. 1) The bending fracture strength of VC coated die steel (STD11, STD61) was lessened with increasing the thickness of the VC coated layer. 2) With increasing the immersing time (imcreasing the thickness of the VC coated layer) the maximum hardness was obtained at 480 minutes holding, after that holding time hardness was decreased. 3) The impact strength of the VC coated die steel was not decreased. In the casse of STD11, it was higher than that of the quenched condition especially at low tempering temperature, and vice versa at high tempering temperature. However in the case of STD61 shows the result to the contrary.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.6
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• pp.73-80
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• 2007

Nanocomposites are used as a new class of polymer system and many researchers have been interested in the clay nanocomposite because of its good mechanical properties, heat resistance, flame retardancy, and barrier property. Modified layered silicates as fillers are dispersed at a nanometer-level within a polymer matrix and then new extraordinary properties are observed. In this study, polypropylene/clay nanocomposites were prepared in a twin screw extruder by the melt compounding method. In order to increase the compatibility of PP with the clay, the MAPP was used as a compatibilizer. And organic modified clays were used as a nanometric filler during the melt extrusion. Through the analysis of SAXS, WAXS, the dispersion of clay was investigated. These nanocomposites compared with a neat polypropylene/talc composite have high modulus, low toughness, and reduced shrinkage at the stable dispersion.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.2
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• pp.115-133
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• 2011

Fiber reinforced polymer composites (FRPs) are being increasingly used for a wide range of engineering applications owing to their high specific strength and stiffness. However, their through-the-thickness performance lacks some of the most demanding physical and mechanical property requirements for structural applications, such as aerospace vehicles and military components. Carbon nanotubes (CNTs) and carbon nanofibers (CNFs), due to their excellent mechanical, thermal and electrical properties, offer great promise to improve the weak properties in the thickness direction and impart multi-functionality without substantial weight addition to FRPs. This paper reviews the progress made to date on i) the techniques developed for integration of CNTs/ CNFs into FRPs, and ii) the effects of the addition of these nanofillers on the interlaminar properties, such as such interlaminar shear strength, interlaminar fracture toughness and impact damage resistance and tolerance, of FRPs. The key challenges and future prospects in the development of multiscale CNT-FRP composites for advanced applications are also highlighted.