• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.672-682
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• 2008

The resistance spot welding of TRIP590 steels was investigated to enhance understanding of weld fracture during tensile-shear strength (TSS) test. The main failure modes for spot welds of TRIP590 steels were nugget pullout and interfacial fracture. The peak load to cause a weld interfacial failure was found to be related to fracture toughness of the weld and the weld diameter. Although interfacial fracture occurred in the samples, the load carrying capacity of the weld was high and not significantly affected by the fracture mode. Substantial part of the weld exhibits the characteristic dimple (or elongated dimple) fractures on interfacial fractured surface, in spite of the high hardness values associated with the martensite microstructures. The high load-bearing ability of the weld is directly associated with the area of ductile fracture occurred in weld. Therefore, the judgment of the quality of resistance spot welds in TRIP590 steels, the load carrying capacity of the weld should be considered as an important factor than fracture mode.

• Journal of Welding and Joining
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• v.14 no.6
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• pp.48-57
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• 1996

The weldability of high purity aluminum-lithium binary alloys has been investigated using the Varestraint test. Autogenous GTAW (gas-tungsten-arc-welds) were run along specimens of different lithium concentration using three sets of welding parameters. Welding voltage was held constant at 10 volts. Welding current (70∼100 amps) and travel speed (23∼33 cm/min) were the parameter varied. Hot-tearing susceptibility varied with lithium content and exhibited a steep peak at 2.6 weight percent lithium. Depth of penetration increased with increasing heat input and lithium concentration. The susceptibility is influenced by the wettability of dendrites by the interdendritic eutectic liquid as well as the time available for back-Siting by eutectic liquid. The welding condition of welding current 70A and travel speed 23 cm/min was showed good resistance to cracking in aluminum-lithium alloys. Suggestions for improving weld cracking resistance are also provided.

• Journal of electromagnetic engineering and science
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• v.2 no.1
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• pp.5-10
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• 2002

We have analized the inverse class-F and class-F amplifiers using their waveforms. From the analytic equations derived from the analysis, we have calculated tole efficiencies, output powers, DC power dissipations, and optimum fundamental load impedances of the inverse class-F and class-F amplifiers. We also have compared them for various operation conditions, which include the same peak current, saute DC power dissipation, same fundamental RF output power, and same fundamental load impedance with different Ron(on-resistance). These analyses have clearly shown the performance limitations, advantages, and guide to the optimized design of the inverse class-F amplifiers.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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• pp.305-308
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• 2008

This paper presents characteristics of soil ionization when high currents such as lightning and switching surge currents are injected into a grounding rod. Soil ionization phenomena are investigated by using both voltage and current signals recorded by oscilloscope. As a result, a critical electric field intensity($E_C$) for ionization is decreased with reduction of grain size. The pre-ionization resistance($R_1$) and post-ionization resistance($R_2$) at the sand with fine grain size are getting lower with increasing current magnitude. Finally, the time to ionization($t_1$) and ionization current peak($t_2$) of fine grain size are significantly shorter than those of medium grain size.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05b
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• pp.66-70
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• 2003

This dissertation is about the development of $BaTiO_{3}$-type PTC(Positive Temperature Coefficient) thermistor by composition method. PTC samples were fabricated after setting the experimental composition equation as $(Ba_{0.95-x}Sr_{0.05}Ca_x)TiO_3\;-\;0.01TiO_2\;-\;0.01SiO_2\;-\;aMnCO_3\;-\;0.2Nb_{2}O_{5}$ and their testing results were analyzed. a PTC thermistor, having the characteristics of relatively low resistance at room temperature and c and a good temperature coefficient, has been developed.

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.61-63
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• 2004

PTC Thermistors specimens were fabricated by added $MnO_2$ as donors, and $Nb_2O_5$ as acceptors and sintered $1250^{\circ}C$/2hrs. Average grain size decreased with increased in added $MnO_2$, and increased with added in $Nb_2O_5$. But, appeared liquid phase as $Bi_2O_3$ and $TiO_2$, affect to grain growth. XRD result, peak strength was lowed then crystallization not well, but, secondary phase were not showed all specimens. All specimens resistance were so high, about $40M{\Omega}$ over, couldn't measured to those resistance and doesn't appear PTCR effect.

• Proceedings of the KIEE Conference
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• 1998.07e
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• pp.1598-1600
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• 1998

When dielectric surface electric field exceed any electric field strength on air, corona discharge is occurred from the dielectric surface. This paper presents corona discharge phenomena on the dielectric in high field were studied under application of ${\pm}DC$ voltage, constitute of the point to plane 20mm gap. The results obtained in experimental are summarized as follow :(1) Corona pulse is appeared periodically after first corona pulse is occurred and the number of corona pulse increases with the instantaneous applied voltage but peak value is not changed greatly.(2)Applied voltage to beccrite and characteristics and peak value of current are almost a straight line. That kind of tendency accorded with characteristics of beccrite resistance.(3)In case of Positive corona, Positive streamers, were progressed greatly to plane electrodes but In case of negative corona, negative streamers smaller than that of Positive corona.

• Physical Therapy Rehabilitation Science
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• v.12 no.2
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• pp.201-205
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• 2023

Objective: Resistance exercise is a necessary element to improve quality of life, and measurement and evaluation of muscle strength provide important information for prescription and management of rehabilitation and exercise programs. This study analyzed the correlation between direct and indirect 1RM for isokinetic maximum torque of the knee joint in order to provide useful information in the field of exercise programs. In addition, the flexion-extension ratio and the difference in left-right deviation were verified. Design: A cross-sectional study Methods: The subjects of this study were 33 healthy adult men and women without medical problems who participated in the health exercise class program at S University in Seoul. The correlation between isokinetic maximum torque and direct and indirect 1RM was analyzed, and a dependent t-test was performed to analyze the flexion-extension ratio and left-right deviation. Results: There was a high correlation between the isokinetic maximum torque and direct and indirect 1RM, and no statistically significant difference was shown between the test methods in the analysis of the flexion-extension ratio and left-right deviation. Conclusions: Isokinetic muscle function measuring equipment is expensive, so it is difficult to use it in local exercise rehabilitation and training sites. Through this study, it was found that direct and indirect 1RM isokinetic maximum torque showed a high correlation, and there was no difference in evaluating muscle function such as flexion-extension ratio and left-right deviation. Therefore, it is considered that the muscle function evaluation using 1RM in general field can be usefully utilized.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.6
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• pp.1022-1025
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• 2008

This paper presents the generation of the high voltage squarewave pulse using distributed RLC circuit. The demonstrated test was performed with the distributed RLC circuit which consists of the resistance, the inductance and the capacitance. Pspice simulation was also conducted about the experiment circuit. The result of the experiment was in good agreement with the result of the simulation. Theoretical analysis of the initial peak value at the squraewave pulse was derived from the results of the experiment and simulation. Additionally, the characteristics of the time delay was analyzed about the spherical gap switch and the surface discharge gap switch, respectively. It is concluded that the surface discharge gap switch is better than the spherical gap switch to reduce the time delay.

• Journal of Korean Society for Atmospheric Environment
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• v.12 no.2
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• pp.131-139
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• 1996

The developent of ceramic combustor is being increased beca- use of the excellent physical properties of ceramic material, that is, high-resistant strength, high emissivity power and high corrosin-resistance. Ceramic combustor has been interested in the application of ultra-lean combustion for low NO$_{x}$ emission and gaseuos waste incineration with good combustion. This experimental study was conducted to investigate the combustion and emission characteristics of wall recess type ceramic combustor with equivalence ratio, mixture flow velocity and wall recess depth as parameters. The results in this study are as follows: 1. Wall recess played a important role to extend flame stability region. 2. The peak temperature of gas was peoportional to equivalence ratio, mixture flow velocity and wall recess depth. 3. The static pressure of mixing chamber and inlet temperature depended on the position of flame zone. 4. NO reduction was achieved by lean mixture without lower combustibility.y.