• Journal of Powder Materials
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• v.18 no.1
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• pp.64-72
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• 2011

Nondestructive instrumented indentation test is the method to evaluate the mechanical properties by analyzing load - displacement curve when forming indentation on the surface of the specimen within hundreds of micro-indentation depth. Resistance spot welded samples are known to difficult to measure the local mechanical properties due to the combination of microstructural changes with heat input. Particularly, more difficulties arise to evaluate local mechanical properties of resistance spot welds because of having narrow HAZ, as well as dramatic changed in microstructure and hardness properties across the welds. In this study, evaluation of the local mechanical properties of resistance spot welds was carried out using the characterization of Instrumented Indentation testing. Resistance spot welding were performed for 590MPa DP (Dual Phase) steels and 780MPa TRIP (Transformation Induced Plasticity) steels following ISO 18278-2 condition. Mechanical properties of base metal using tensile test and Instrumented Indentation test showed similar results. Also it is possible to measure local mechanical properties of the center of fusion zone, edge of fusion zone, HAZ and base metal regions by using instrumented indentation test. Therefore, measurement of local mechanical properties using instrumented indentation test is efficient, reliable and relatively simple technique to evaluate the tensile strength, yield strength and hardening exponent.

• Proceedings of the Korean Vacuum Society Conference
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• 2008.02a
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• pp.218-218
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• 2008

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.214-214
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• 2009

While critical properties of BSCCO wires rely considerably on grid direction upon BSCCO and have very complicated mechanism of generating a superconducting phase, making it difficult to improve properties of wires, YBCO thin-film wires which can be formed in a superconducting phase upon metal board through vapor deposition processing can get excellent direction and reduce manufacturing costs with more flexibility in improving critical properties; thus, they will be suitable for instrument application in the future. Contrary to BSCCO wires for which thick silver alloy covering materials should inevitably be used, moreover, YBCO thin-film wires have an advantage of making thickness and quality of covering materials different by usage. Such a property can be an important element to widen application of wires by presenting possibility of using thin-film wires as superconducting material for fault current limiter as well as for high power current application. In this study we intend to prepare YBCO thin-film wires with different stabilizer layers to analyze current application and current restriction properties by stabilizer layers on the basis of detailed researches on changes in current classification properties below critical value.

• Journal of Industrial Technology
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• v.36
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• pp.39-43
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• 2016

The purpose of this study is to determine and compare the mechanical and flow properties of polyvinylsiloxane impression pastes. Twelve polyvinylsiloxane impression materials were used. As mechanical properties, tensile strength and tear resistance were measured. Impression materials are subjected to tensile stresses when they are removed from the oral cavity and from stone models and tear resistance is the ability of the material to resist tearing under a tensile stress. Flow is dependent on the ability of the material to resist shear forces. Flow tests were performed to determine the handling characteristics and was measured using a shark fin testing device. An impression material must be able to penetrate the narrow subgingival sulcus and tight interproximal areas. Therefore, it must be able to resist the shear forces as it is pushed between tooth and gingival walls. It is necessary to understand the properties of interocclusal recording materials and is considered that the results obtained in this study will provide guideline information for the manufacturing of impression materials and for selecting appropriate impression materials.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.309-309
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• 2009

In-Ga-Zn-O (IGZO) has drawn much attention as a compatible material for transparent thin film transistors (TTFT) channel layer due to its high mobility and optical transparency at low processing temperatures. In this work, we investigated the effect of oxygen ambient on structural, electrical and optical properties of amorphous In-Ga-Zn-O (IGZO) thin films by using pulsed laser deposition (PLD). The films were deposited at various oxygen pressures and the structural, electrical and optical properties were investigated. X-ray diffraction (XRD) analysis showed that amorphous IGZO films were grown at all oxygen pressures. The surface morphology and optical properties with various oxygen pressures were studied by field emission scanning electron microscopy (FE-SEM) and UV-VIS spectroscopy, respectively. The grain boundary was observed more apparently and the calculated optical band gap became larger as oxygen pressure increased. To examine the electrical properties, Hall-effect measurements were carried out. The films showed high mobility.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.125-128
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• 2001

In this wort, the $Na^+-MMT$ has organically modified with silane intercalant to prepare the polymer/clay nanocomposites. The pH. X-ray diffraction (XRD), and contact angles were used to analyze the surface properties of clay and the exfoliation phenomenon of clay interlayer, The mechanical interfacial properties of epoxy/clay nanocomposites were investigated by three-point bending test. From the experimental results. the surface modification made by silane intercalant on clay surface leads to an increase of distance of silicate layers, surface acid value. and electron acceptor parameter of organoclay. The treatments are also necessary and useful for epoxy to intercalate into the interlayer by interacting of electron donor-accepter between basic epoxy and clay surface. The mechanical interfacial properties of the nanocomposites was improved by the presence of dispersed clay nanolayer containing low content of organoclay in comparison with the conventional, which increase the interfacial adhesion between dispersed clay and epoxy resins.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.12
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• pp.881-887
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• 2015

The stiffness and natural frequencies for blades, flexbeam, and torque tube of bearingless rotor system are measured to determine the material input properties such as mass distributions and stiffness distribution for the rotor dynamics and load analysis. The flap stiffness, lag stiffness, and torsional stiffness are calculated by measuring section strain or twist angle, gages position, and applied loads through bending and twist tests. The modal tests are undertaken to find out the natural frequencies for flap, lag, torsion modes in non-rotating conditions. The stiffness values and mass properties are tuned and updated to match prediction frequencies to the measured frequencies. The rotorcraft comprehensive code(CAMRAD II) is used to analyze the natural frequencies of the specimens. The analysis results with the updated material properties agree well with the measured frequencies. The updated properties will be used to analyze the rotor stability, dynamic characteristics and loads for the rotor rotation test in a whirl tower.

• Tribology and Lubricants
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• v.32 no.2
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• pp.39-43
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• 2016

Magnetorheological elastomers (MREs) are a type of “smart” material, and their properties can be controlled rapidly and reversibly under the influence of an external stimulus. The application of an external magnetic field can change the shear modulus, hardness, and friction coefficient of MREs. The friction can cause vibration; moreover, the vibration can affect friction. The change of friction depends on the relative motion, normal force, roughness of the rubbing surfaces, material type, temperature, lubrication, relative humidity, and vibration condition. As MREs are a type of “smart material,” their friction coefficient can be reduced by applying an external magnetic field—the applications of this feature in engineering have been widely studied. However, the friction properties of MREs under vibration have not been tested to date. In this study, MRE samples and a reciprocating friction tester were fabricated. The friction coefficient was measured to evaluate the friction properties under various vibration conditions; subsequently, the wear depth and wear surface profile of the MRE were observed in order to evaluate the wear properties. The results show that the friction coefficient of the MREs decreased when a magnetic field was applied. Moreover, the friction coefficient decreased when the vibrational amplitudes increased. The wear depth of the MRE also decreased as the vibrational amplitudes increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.260-260
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• 2010

In recent years, polymer/clay nanocomposites have generated a great interest, both in industry and in academia, because they often exhibit remarkable improvement in material properties when compared with the virgin polymer or conventional micro and macro-composites. Among these properties are stiffness, strength, dimensional stability and permeability. [1-3] The dispersion of hydrophilic silicates in a hydrophobic matrix like Polyethylene (PE) is difficult because of the difference in character between PE and Montmorillonite (MMT). Therefore, it is necessary to modify PE with polar groups, which can increase the hydrophilicity of PE. In this study, High density polyethylene (HDPE)/$Mg(OH)_2$/Montmorillonite (MMT) nanocomposites having a various compositions were prepared by a melt blending technique with an internal mixer and properties namely mechanical, morpology, rheological and thermal properties were investigated

• Steel and Composite Structures
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• v.21 no.3
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• pp.517-536
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• 2016

Thick steel plate is commonly found with mega steel structures but its properties have not been fully explored. Grade Q345GJ-C steel plate with thickness ranging from 60 mm to 120 mm are studied in this paper. Both the static and cyclic performance of material in different directions (horizontal and through-thickness directions) and locations (outer surface, 1/4 thickness and mid-depth) are experimentally obtained. The accumulative damage during cyclic loading is also calculated by using bilinear mixed hardening (BMH) constitutive relationship together with the Lemaitre's damage model. Results show that the static properties are better at the outer surface of thick steel plates than those at mid-depth. Properties in through-thickness direction are similar to those at mid-depth in the horizontal direction. The cyclic performance at different locations of a given plate is similar within the range of strain amplitude studied. However, when damage parameters identified from monotonic tensile tests are included in the numerical simulation of cyclic loading tests, damage is found accumulating faster at mid-depth than close to outer surface.