• Advanced Composite Materials
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• v.18 no.4
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• pp.395-413
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• 2009

Impact tests on high-strength membrane materials under biaxial loads were experimentally conducted in order to evaluate influence of biaxial loads on impact fracture of the membrane materials for the inflated applications. Cruciform specimens of the membrane materials were fabricated for applying biaxial loadings during the impact test. A steel ball was shot using a compressed nitrogen gas gun, and struck the membrane specimen. Impact tests on uniaxial strip specimens were also conducted to obtain the effect of specimen configuration and boundary condition on the impact fracture. The results of the measured crack length and the ultra-high speed photographs indicate the impact fracture properties of the membrane fabrics under biaxial loadings. Crack length due to the impact increased with applied tensile load, and the impact damages of the cruciform membrane materials under biaxial loadings were smaller than those of under uniaxial loadings. Impact fracture of the strip specimen was more severe than that of the cruciform specimen due to the difference of boundary conditions.

• Corrosion Science and Technology
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• v.5 no.5
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• pp.181-188
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• 2006

In this study, the characteristics of the experimentally produced high N-high Cr bearing stainless steels are discussed as a part of applications of materials for FGD (Fuel Gas Desulfurization) system of thermal power plants or for power plants using seawater as coolant. Corrosion resistance of developed alloys is especially investigated in detail. Corrosion characteristics of vacuum melted cast are shown to be superior to that of air melted one. From the viewpoint of CPT, It is estimated that the differences of corrosion resistance are $21.8^{\circ}C{\sim}24.6^{\circ}C$ at PRE 40 and $8^{\circ}C{\sim}12.4^{\circ}C$ at PRE 50, and the gaps becomes bigger as the PRE values are lower. In the evaluation of corrosion resistance in alloy A2501, Z3101, and A3301 according to Cr concentration, alloy A3301 shows a deviation from the general tendency in chloride solutions. It has relatively high PRE value as 48.6, but it has relatively poor pitting resistance. It is, however, difficult to observe a specific phase except ferrite in microstructure analysis and neither detects special phase such as sigma phase.

• Progress in Superconductivity and Cryogenics
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• v.17 no.3
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• pp.33-36
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• 2015

A liquid nitrogen ($LN_2$) is usually used to be a coolant and insulant for a HTS coil system. HTS wires for a superconducting apparatus may be surrounded by gaseous nitrogen ($GN_2$) due to film boiling generated by a quench or voids occurred by electrical breakdown. The increased maximum electric field intensity at $GN_2$ may result in the degradation of dielectric strength of a HTS coil system. In this paper, a study on the dielectric characteristics of a composite insulation system composed of $LN_2$ and $GN_2$ is performed. A sphere-to-plane electrode system made with stainless steel is used to perform the experiments under AC and lightning impulse voltage condition. A sphere electrode is surrounded by $GN_2$ and a plane electrode is immersed into $LN_2$ to conduct dielectric experiments with a composite insulation system. The dielectric experiments are performed according to the level of $LN_2$ from the plane electrode to a sphere electrode. It is found that the dielectric characteristics of a composite insulation system are dependent on the level of $LN_2$ and the field utilization factor of an electrode system.

• Progress in Superconductivity and Cryogenics
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• v.5 no.3
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• pp.30-33
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• 2003

1MVA high temperature superconducting (HTS) transformer with double pancake windings made of BSCCO-2223 HTS tapes was designed and manufactured. And prototype transformer with the same capacity was manufactured also. The each rated voltage of the HTS transformer is 22.9 kV and 6.6 kV. Four parallel BSCCO-2223 HTS tapes were wound in the double pancake windings of low voltage side. In order to distribute the currents equally in each HTS tapes, the three times transposition was performed between the double pancake windings. The windings of prototype transformer were wound using copper tape with the same size as BSCCO-2223 HTS tape. The core of the transformer was designed and manufactured as a shell type core made of laminated silicon steel plate. The several characteristics tests for the prototype transformer were performed in liquid nitrogen and insulation tests were accomplished also.

• Journal of Korean Society for Atmospheric Environment
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• v.19 no.1
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• pp.13-23
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• 2003

A local wind model and a three dimensional local environmental model including advection, diffusion, deposition. and photochemical reactions were performed at Gwangyang Bay, Korea, to predict air flow and air pollutants concentrations. A large grid was used, and nesting method was employed for small grid calculation. From the meterological module simulation, we were able to reproduce local wind characteristics such as sea/land winds and mountain/valley winds simulation at Gwangyang Bay. In addition, the concentration module showed high concentration regions at Yosu industrial complex, Gwangyang steel company. and Container anchor. It was also seen that air pollutants were dispersed by sea/land winds. A comparison between the measurement and the prediction of sulfur dioxide and nitric oxide, which are relatively low-reacted pollutants, was performed. However, the measured nitrogen dioxide and ozone concentrations were higher than the simulated ones. Particularly, ozone concentration between 8 a..m. and 8 p.m. agreed well, but the measured ozone during the rest of time were generally higher.

• Journal of Welding and Joining
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• v.19 no.3
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• pp.317-324
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• 2001

This study deals with high power Nd:YAG laser welding of thin steels for small pressure vessels. Full penetration welding at the overlap joint was performed so as to assure sufficient weld strength. Results showed that mid-depth weld size reduced drastically with increasing the travel speed. Position of focus had little effect on the bead formation even though short focal system was used. However, the shape factor and the bead width had closely related with the position of focus. Based on the microstructural inspection, acceptable weld was obtained when the overlap clearance was controlled up to 20% of the base metal thickness. In the case that the joint contained more clearance than the critical value, both the tensile shear strength and the tear strength were reduced. Results also demonstrated that shielding gases were proved to play a key role as far as the bead formation characteristics was taken into consideration. Blowing dry air through 5mm in diameter nozzle produced narrower bead cross-section than that of argon or nitrogen shielding.

• Journal of Welding and Joining
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• v.20 no.1
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• pp.26-33
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• 2002

This study was undertaken to obtain the fundamental knowledges on the weld deflects and it's realtime monitoring method. The paper describes the results of high speed photography, acoustic emission (AE) detection and plasma light emission (LE) measurements during $CO_2$ laser welding of STS 304 stainless steel and A5083 aluminum alloy in different welding condition. The characteristic frequencies of plasma and keyhole fluctuations at different welding speed and shield gases were measured and compared with the results of Fourier analyses of temporal AE and LE spectra, and they had considerably good agreement with keyhole and plasma fluctuation. Namely, the low frequency peaks of AE and LE shifted to higher frequency range with the welding speed increase, and leer the argon shield gas it was higher than that in helium and nitrogen gases. The low frequencies dominating in fluctuation spectra of LE probably reflect keyhole opening instability. It is possible to monitor the weld bead deflects by analyzing the acoustic and/or plasma light emission signals.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1317-1323
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• 2002

This paper describes the comparison of calculated effective stress with experimental one in austenitic heat resistant steels, STS310J1TB and STS310S with and without a small amount of Nb and N. Based on a solute atoms diffusion model, contribution from soluble nitrogen to the high-temperature strength was numerically examined for austenitic heat-resisting Fe-Cr-Ni-N(STS310J1TB) and Fe-Cr-Ni (STS310S) alloys. The solute atmosphere dragging stress of dislocation was calculated in optional dislocation velocity of STS310J1TB and STS310S at $650^{\circ}C$, $675^{\circ}C$ and $700^{\circ}C$. As a result of the numerical calculation, the solute atmosphere dragging stress of STS310J1TB was about 50 times larger than that of STS310S. When the temperature became high, the maximum value of solute atmosphere dragging stress was small and the velocity of moving dislocation was fast. From the relationship between the dislocation rate and the solute atmosphere dragging stress, the relation of both was proportional and the inclination is about 1 in the level with low velocity of moving dislocation. From above results, the mechanism of dislocation movement in STS310J1TB was the solute atmosphere dragging stress. The solute atmosphere dragging stress, which was calculated from the numerical calculation was close to the effect stress in stress relaxation tests.

• Progress in Superconductivity
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• v.4 no.1
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• pp.86-89
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• 2002

In this paper, the design of a IMVA single-phase high temperature superconducting(HTS) power transformer with BSCCO-2223 HTS tapes is presented. The rated voltages of each sides of the transformer are 22.9 ㎸ and 6.6 ㎸, respectively The winding of 1MVA HTS transformer is consisted of double pancake type HTS windings, which have advantages of insulation and distribution of high voltage, and are cooled by subcooled liquid nitrogen of 65K. Four HTS tapes were wound in parallel for the windings of low voltage side and the four parallel conductors are transposed. The design of 1MVA HTS transformer, a shell type core made of laminated silicon steel plate is chosen, and the core is separated with the windings by a cryostat with a room temperature bore. The cryostat made of non-magnetic and non-conducting material and a liquid nitrogen sub-cooling system is designed in order to maintain the coolant's temperature of 65K. For electromagnetic analysis of 1MVA HTS transformer, a finite element method of an axis of symmetry is used. The maximum perpendicular component of magnetic flux density of pancake windings is about 0.15T. And through analyzing the magnetic field distribution, an optimal winding arrangement of 1MVA HTS transformer is obtained.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.48-51
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• 2003

A 1 MVA transformer with BSCCO-2223 high Tc superconducting (HTS) tapes was designed. The rated voltages of each sides of the transformer are 22.0 kV and 6.6 kV respectively. Double pancake HTS windings, which have advantages of insulations and distribution of high voltage, were adopted. Four HTS tapes were wound in parallel fer the windings of low voltage side. Each winding was composed of several double pancake windings made of four parallel conductors were transposed in order to distribute the currents equally in each conductor. A core of the transformer was designed as a shell type core made of laminated silicon steel plate and the core is separated with the windings by a cryostat with a room temperature bore. The operating temperature of HTS windings will be 65K with liquid nitrogen, and a cooling system using a cryocooler was proposed and designed conceptually. This HTS transformer is going to be manufactured in near future based on the design parameters presented in this paper.