• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.433-433
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• 2013

Graphene, $sp^2$-hybridized 2-Dimension carbon material, has drawn enormous attention due to its desirable performance of excellent properties. Graphene can be applied for many electronic devices such as field-effect transistors (FETs), touch screen, solar cells. Furthermore, indium tin oxide (ITO) is commercially used and sets the standard for transparent electrode. However, ITO has certain limitations, such as increasing cost due to indium scarcity, instability in acid and basic environments, high surface roughness and brittle. Due to those reasons, graphene will be a perfect substitute as a transparent electrode. We report the graphene synthesized by inductive coupled plasma enhanced chemical vapor deposition (ICP-PECVD) process on Cu substrate. The growth was carried out using low temperature at $400^{\circ}C$ rather than typical chemical vapor deposition (CVD) process at $1,000^{\circ}C$ The low-temperature process has advantage of low cost and also low melting point materials will be available to synthesize graphene as substrate, but the drawback is low quality. To improve the quality, the factor affect the quality of graphene was be investigated by changing the plasma power, the flow rate of precursors, the scenario of precursors. Then, graphene film's quality was investigated with Raman spectroscopy and sheet resistance and optical emission spectroscopy.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.3
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• pp.1-7
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• 2007

The hollow RC(Reinforced concrete) column has the effect of reducing weight and materials compared to solid RC column. However, the hollow RC column shows a low ductile behavior due to brittle failure of inside concrete. To overcome this problem, the internally confined hollow reinforced concrete column has been developed. In this study, the behavior of internally confined hollow RC columns were evaluated with safety ratio, ductility, total material cost, the total weight of the pier, etc. The hollow ratio is varied from 0.50 to 0.85.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.1
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• pp.23-32
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• 2018

In this study, we conducted a shake table test to verify the seismic performance of the paneling system with steel truss composed of bolt connections. The control group was set to the traditional paneling system with steel truss connected by spot welding method. Test results showed that the bolted connection type paneling system has excellent deformation capacity without cracking or brittle fracture of the steel truss connection parts compared to the welding type paneling system. Furthermore, in the bolted connection type, slight damage occurred at the time of occurrence of the same story drift angle as compared with the existing method, it is considered that it has excellent seismic performance. In compliance with the performance-based design recommended for the current code (ASCE 41-13) on non-structural components, it is judged that in the case of the bolted connection type paneling system, it can be applied to all risk category structures without restriction. However, in the case of traditional paneling system with spot welding method, it is considered that it can be applied limitedly.

• Earthquakes and Structures
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• v.7 no.5
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• pp.691-704
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• 2014

Reinforced concrete (RC) shear walls are commonly used for building structures to resist seismic loading. While the RC shear walls can have a high load-carrying capacity, they tend to fail in a brittle mode under shear, accompanied by forming large diagonal cracks and bond splitting between concrete and steel reinforcement. Improving seismic performance of shear walls has remained a challenge for researchers all over the world. Engineered Cementitious Composite (ECC), featuring incredible ductility under tension, can be a promising material to replace concrete in shear walls with improved performance. Currently, the application of ECC to large structures is limited due to the lack of the proper constitutive models especially under shear. In this paper, a new Cyclic Softening Membrane Model for reinforced ECC is proposed. The model was built upon the Cyclic Softening Membrane Model for reinforced concrete by (Hsu and Mo 2010). The model was then implemented in the OpenSees program to perform analysis on several cases of shear walls under seismic loading. The seismic response of reinforced ECC compared with RC shear walls under monotonic and cyclic loading, their difference in pinching effect and energy dissipation capacity were studied. The modeling results revealed that reinforced ECC shear walls can have superior seismic performance to traditional RC shear walls.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.6
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• pp.1013-1028
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• 2017

This paper presents key findings obtained from the numerical experiment investigating into the use of the cylindrical cavity for rock splitting operations. The stress and strain path analyses were carried out in order to provide a better insight into the crack formation. The principal stress analysis carried out along the crack line using the results obtained from these numerical analyses allowed the failure of the brittle material and the crack propagation to be investigated. This paper also suggested possible reasons for the change in crack direction observed during the rock splitting operations using the results obtained.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.110-117
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• 2002

In a strengthened bridge deck which received increased service loads, failure patterns of bridge deck vary depending on deck thickness, compressive strength of concrete, yielding strength of reinforcement, reinforcement ratio and additional strengthening ratio. General failure pattern that is most commonly reported as punching shear failure after the main rebar yields, followed by yielding of distributing rebar. In this paper, by Proposing a limit to the amount of strengthening material, a brittle failure can be prevented and a ductile failure mode similar to that developed in unstrengthened deck is derived. In order to calculated the limit strengthening ratio, the yield line theory and previously proposed plastic punching shear model have been used

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.831-836
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• 2000

During machining, since more than 50% compliance of the cutting point in machine tool structures comes from headstocks, with the remainder coming from beds, slides and structural joints, the structural analysis of the headstock is very important to improve the static and dynamic performances. Especially, in case of machining hard and brittle materials such as glasses and ceramics with the grinding machine, the reinforced headstock with the high damping material is demanded. Since the fiber reinforced composite materials have excellent properties for structures, owing to its high specific modulus, high damping and low thermal expansion, it is expected that the dynamic and thermal characteristics of the headstock will be improved if they are employed as the materials fur headstock. In this paper, the design and the manufacturing methods as well as the static and dynamic characteristics of a steel-composite hybrid headstock were investigated analytically and experimentally to improve the performance of the grinding machine system.

• Earthquakes and Structures
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• v.13 no.1
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• pp.29-38
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• 2017

Stone masonry is one of the oldest construction types due to the natural and free availability of stones and the relatively easy construction. Since stone masonry is brittle, it is also very vulnerable and in the case of earthquakes damage, collapses and causalities are very likely to occur, as it has been seen during the last Italian earthquake in Amatrice in 2016. In the recent years, some researchers have performed experimental tests to improve the knowledge of the behaviour of stone masonry. Concurrently, there is the need to reproduce the seismic behaviour of these structures by numerical approaches, also in consideration of the high cost of experimental tests. In this work, an alternative simplified procedure to numerically reproduce the diagonal compression and shear compression tests on a rubble stone masonry is proposed within the finite element method. The proposed procedure represents the stone units as rigid bodies and the mortar as a plastic material with compression and tension inelastic behaviour calibrated based on parametric studies. The validation of the proposed model was verified by comparison with experimental data. The advantage of this simplified methodology is the use of a limited number of degrees of freedom which allows the reduction of the computational time, which leaves the possibility to carry out parametric studies that consider different wall configurations.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.6
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• pp.87-93
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• 1994

This paper describes on the establishment of an optimal internal grinding conditions for the purpose of improving the grinding efficiency against to the high-speed grinding. Through the fundamental grinding tests for the brittle and hardened material, we are concluded that high-speed internal grinding is effective to improve the grinding accuracy as well as the grinding efficiency. The obtained results are as follows: (1) Under the speed ratio $(V_w/V_g)$ is constant, it is possible to increase the grinding efficiency with satifying the constraint conditions. (2) Increasing the wheel velocity, surface roughness and out-roundness are improved. (3) Under the wheel depth of cut is constant and increasing the speed ratio, workpiece residual stress is decreased. The described method, in this paper, is capable of determining the optimum internal grinding conditions taking into account some constraint conditions, and practical algorithm for optimum internal grinding conditions are presented.

• Journal of Korea Foundry Society
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• v.20 no.1
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• pp.21-28
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• 2000

Ni and Ni-Cr porous metals which are estimated to be easy to fabricate by squeeze casting are used as strengtheners for composite materials. As a matrix material, Al-7%wtSi-0.3 wt%Mg(AC4C) has been used. In case of Ni/AC4C and Ni-Cr/AC4C composite, $750^{\circ}C$ melt temperature and minimum 25 MPa squeezing pressure are needed to produce sound composite materials. The observation of interfacial reaction zone at various heat treatment condition showed that solutionizing temperature of above 520^{\circ}C$, the interfacial reaction zone increased proportionally with increasing heat treatment tim and reaction products formed by interfacial reaction are mainly composed of $Al_3Ni$ and $Al_3Ni_2$ phases. The tensile strength of Ni/AC4C and Ni-Cr/AC4C composite is lower than the matrix metal and this can be explained by the brittle intermetallic compounds formed at the interface of Ni and Ni-Cr reinforcements. But the properies of hardness, wear resistance and thermal expansion are better than the matrix due to the strengthening effect of Ni-Cr porous metals.