• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.2
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• pp.121-128
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• 2005

This study focuses on evaluating the reliability index of a deck of RC slab having chloride contamination and studying the relation of grades of rebar corrosion and the reliability index of a bridge deck For this purpose, first, the failure probability related to flexural strength was calculated using a model for deterioration, which contains the application of deicing salts that usually causes significant long-term deterioration and reduction in the structural safety for strength of structure. And also, according to the depth of covering, the chloride contents depending on time due to depths of RC slab deck, the appearance time for initial corrosion of rebar and the occurrence time for split of covering were investigated using a MCS method.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.403-408
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• 2003

The erosion behavior of :artificially aged HK40 steel was investigated. Erosion tests were conducted at room temperature, $200^{\circ}C$ and $400^{\circ}C$ using $Al_2O_3$ particles. Erosion rates increased with increment of temperature. The maximum erosion rate increased with the impingement angle of 30 degree. The erosion rate increased, reached the maximum at 1000 hours, and after that, decreased with heat treatment time. The mechanism of erosion seems to be the cutting wear which is very much associated with the strength of material. As results, the erosion rates were rather affected by the tensile strength and the strain hardening coefficient than the hardness and the yield strength. Such changes of material properties would be caused by the change of micro-structure due to the precipitation of carbide and the dissolution of solid element within matrix during the heat treatment.

• Composites Research
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• v.34 no.6
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• pp.421-425
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• 2021

In this study, thermoplastic composites were manufactured using a thermoplastic resin (PEEK) with the same melting temperature and a highly heat-resistant carbon UD tapes with different carbon fibers (Type A, Type B). And the bonding characteristics and mechanical characteristics of each of the two produced thermoplastic composites by induction heating welding were examined. The bonding characteristics and mechanical characteristics of the thermoplastic composites were performed using C-Scan and B-Scan, which is a non-destructive inspection, and the single lap shear test, respectively. The temperature of the carbon composites surface was monitored using a thermal image camera.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.108-114
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• 2018

Degradations of durability and aesthetic performance in concrete happen during service life due to surface deterioration and dirt stains. Recently, many researches have been performed on self-cleaning and surface enhancement through surface impregnant using photocatalytic reaction with VOCs(Volatile Organic Compounds) removal. This paper is for preliminary study on surface impregnation with silicate and photocatalysis - $TiO_2$. For the work, two types of silicate based impregnants(CS - Coloidal Silica and SC - Sodium Alumina Silicate) are considered. Several tests for viscosity and surface tension are performed, and pull-off test on impregnated concrete is performed. For the surface impregnated concrete, $TiO_2$ is absorbed through submerging and spraying conditions. Through compressive strength test and SEM analysis, it is evaluated that spraying $TiO_2$ on surface impregnated concrete after 30min. of drying period is very effective both for strength enhancement and surface densification.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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• pp.2116-2124
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• 2001

It's required mechanical properties of in-service facilities to maintain safety operation in power plants as well as chemical plants. In this studdy the four classes of the thermally aged 1Cr-lMo-0.25V specimens were prepared using an artificially accelerated aging method at 630$\^{C}$. Ultrasonic tests, tensile tests, K$\_$IC/ tests and hardness tests were performed in order to evaluate the degree of degradation of the material. The mechanical properties were decreased as degraded, but the attenuation coefficient and the harmonic generation level of a ultrasonic signal were increased. Expecially the nonlinear parameter derived from the harmonic generation level is sensitive and will be a good parameter to evaluate the material degradation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1672-1677
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• 2005

The Heat exchanger to be used in the place of business that is presented an utility period comes to be long and the problem of the length of life shares by the manufacture course and using environment factor. Consequentl, it is came to the front problem of inspection, repair, exchange, the utility stopping, safety and confidence. As a result the possibility which the large safety accident can happen comes to be high. It leads mostly to the large accedent when the explosion accident happens. to keep this, The system which the regular period passes to disuse the structure is prepared but The phenomenon which Time and the strength characteristic of the material change, namely Deradation. but It can't be a preventable solution by accident to the damage. Consequentl, This research can take important role to prevent an every kind accident for domestic pressure vessel by evaluating the mechnical characteristic change of meterial, the structure safety and residual life etc.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05e
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• pp.31-34
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• 2003

폴리머 애자의 장기성능예측을 위하여 많은 수단과 측정방법이 연구되어 왔다. 그러나 폴리머 애자에 있어서 성능저하는 대부분 하우징 재료의 열화에 기인되고 있어 예측 및 진단목적의 연구가 하우징 재료의 가속열화에 초점이 맞추어져 있다. 폴리머 애자는 초고압 절연성능과 기계적 강도가 우수하여 송배전 설비에 많이 사용되고 있지만 애자의 형상과 장기성능과의 관계가 정량적으로 규명되어 있지 않아 개발하는 회사는 물론 사용하는 전력회사가 함께 어려움을 가지고 있다. 폴리머 애자의 형상이 폴리머 애자의 장기 성능에 어떻게 영향을 주는 지를 비교분석하고 평가하는 연구가 필요한 시점이다. 본 연구에서는 규칙 교대 갓, 불규칙 교대 갓의 폴리머 애자를 조립방식으로 제작하고, 규칙 교대 갓의 폴리머 애자를 일체형 진공사출 방식으로 제작을 하여 건조섬락전압, 주수섬락전압, 오손섬락전압을 측정하였다. 오손섬락전압은 주수섬락에 비하여 60% 정도 감소함을 보였고 불규칙한 교대 갓의 폴리머 애자의 경우 특성의 편차가 크게 나타났다. 폴리머 애자의 경우 소재의 우수한 특성도 중요하지만 형상적인 인자도 중요한 설계요소이므로 최적화 방안이 요구된다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2860-2870
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• 1994

When crack are detected in aged turbine rotors of power plants, information on fracture resistance of the aged material at operating temperature is needed for determination of critical loading condition and residual life of the turbine. In this study, fracture toughness (J$_lc$) and tearing modulus(T$_mat$) of virgin and thermally degraded 1Cr-1Mo-0.25V steel, which is one of the most widely used rotor steels, were measured at 538.deg. C according to ASTM E813 and ASTM E1152, respectively. Five kinds of specimen with different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C.$ It was observed that J$_lc$ and T$_mat$ value decreased as the degradation level increased. Analysis of microstructures using a scanning electron microscope showed that the decrement of J$_lc$ is related to segregation of impurities at grain boundaries. It was also verified that the DC electric potential drop method is accurate and reliable for crack length monitoring at elevated temperature.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.108-113
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• 2007

In this report, stress corrosion cracking generation due to pipe material degradation in the primary stage of the nuclear power plant was investigated. Firstly, after artificially degrading the CF8A steel during 2, 4, and 6 months in actual temperature, $400^{\circ}C,$ assessed corrosion susceptibility of the degraded material following ASTM G5 standard. And next, the S.C.C. tests for the degraded material were conducted under the condition of $60^{\circ}C,$ 2wt.% H2BO3+Li70H solution, 0.8 oy. From the results, Corrosion rates linearly increased with degradation period and solution temperature increase. And both the raw material and the degraded materials were not failed in the S.C.C. test condition. In spite of long time test (about 3,900 hrs) under S.C.C. condition, surface pits or surface corrosion by the electro chemical reaction were not observed. And also, even though the nondestructive DCPD and ACPD methods were applied to on-line monitor the S.C.C. failure processes it was impossible because the surface pits and cracks were not generated.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.398-403
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• 1999

Studies on the electrical treeing deterioration and dielectric breakdown phenomena in the polymeric insulator of polyethylene and epoxy resin were carried out. Block type samples with needle-plane electrode geometry were electrically stressed and the tree pattern from the needle tip was observed. In LDPE the density of electrical tree was very high and its pattern was bush type. For the case of XLPE, branched tree was observed. As temperature and SN content increased, the dielectric breakdown voltage decreased and the treeing phenomena became more complicated. Fan type cracks were observed around the conducting tree path in the brittle DGEBA/MDA system.