• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.11a
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• pp.213-218
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• 2008

Recently automatic construction system is attended in construction domains because of the increase of aged workers and the shortage of the experienced. The research level of automatic construction system in Korea will soon attain to the stage of full automation like Japan, which is the highest level in the world. However, in the fully automated level, it is difficult for the automatic system to operate flexibly like the human in various work condition. In the result, the higher the level of automation in the system is, the less efficient the automatic system work in the site. So, it's necessary the development material design to compensate for the flexibility shortage of the system. Therefore, this study proposes the development process to material design suitable for automatic construction system using QFD technique.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.157-162
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• 2001

Fretting is a potential degradation mechanism of structural components and equipments exposed to various environments and loading conditions. The fretting degradation, for example, can be observed in equipments of nuclear, fossil as well as petroleum chemical plants exposed to special environments and loading conditions. It is well known that a cast stainless steel(CF8M) used in a primary reactor coolant(RCS) degrades seriously when that material is exposed to temperature range ken $290^{\circ}C{\sim}390^{\circ}C$ for long period. This degradation can be resulted into a catastrophical failure of components. In the present paper, the characteristics of the fretting fatigue are investigated using the artificially aged CF8M specimen. The specimen of CF8M are prepared by an artificially accelerated aging technique holding 1800hr at $430^{\circ}C$ respectively. Through the investigations, the simple fatigue endurance limit of the virgin specimen is not altered from that obtained from the fatigue tests imposed the fretting fatigue. The similar tests are performed using the degraded specimen. The results are not changed from those of the virgin specimen. The significant effects of fretting fatigue imposed on both virgin and degraded specimen on the fatigue strength are not found.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.3
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• pp.7-12
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• 1991

Effects of Mo content and aging conditions on the amount of retained austenite and mechanical properties of 18 Ni maraging steels were investigated. Maraging steels were fabricated with variation of Mo content. 3, 5, 7, 9% and heat treated by austenitizing at $840^{\circ}C$ for 1 hour and then aged at $480^{\circ}C$ for 0.5~100 hours. It was found that the amount of retained austenite after aolution treatment was negligible up to 5% Mo. 8 and 11 volume percents of retained austenite were obtained with 7 and 9% Mo respectively. The maximum hardness and yield strength without great loss of impact toughness were attained in the range of 4~8 hours of aging time at $480^{\circ}C$ with 5% Mo. It was concluded, as a result, that the optimum Mo content for the good combination of strength and toughness is to be 5% Mo.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.3
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• pp.155-159
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• 1994

As Cr-Mo-V steels have excellent mechanical and creep properties at elevated temperatures, they are extensively used in power plants. However, the steam turbine components are supposed to have suffered material degradation during long-term service at elevated tenperatures. Many efforts have been made to assess the safety and residual life of these components by means of non-destructive methods such as plastic replication, hardness and electric resistance techniques. Recently, a parameter correlating hardness changes during long-term heating to those during creep was introduced and it was named 'G parameter'. The electric resistivity as well as hardness are affected by damage accumulation, but there have been no efforts to correlate G parameter to resistivity changes. In this study, relationship between G parameter and changes in electric resistivity was investigated using artificially aged Cr-Mo-V steel. It is well understood that G parameter can be applied to electric: resistance techmique.

• Journal of Power System Engineering
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• v.6 no.1
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• pp.61-67
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• 2002

15Cr-5Ni 석출강화 스테인리스강 3종류의 피로균열 발생과 성장 특성 및 파괴인성에 대하여 노치함수로서 연구하였다. 3종류강의 열처리 조건은 $482\;^{\circ}C,\;579\;^{\circ}C$ 및 $621\;^{\circ}C$이다. $621\;^{\circ}C$에서 4시간동안 열처리한 시험편 C는 약 $280\;MPa\;\sqrt{m}$의 가장 높은 파괴인성을 보였으며, 3종류에서 피로균열 성장이 가장 늦었다. $482\;^{\circ}C$에서 1시간 열처리한 시험편 A에서, 피로균열발생한계, ${\Delta}k{\rho}$, 는 노치반경0.3 mm에서 약 $280\;MPa\;\sqrt{m}$의 가장 높은 값을 보였다. 시험편 A는 시험편 B와 C보다 피로균열 성장이 빨랐지만, 피로균열 발생이 늦었다. 예 하중에 의한 노치선단의 압축잔류응력은 노치 시험편의 피로강도 향상에 유용한 방법이었다.

• Korean Journal of Veterinary Research
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• v.51 no.2
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• pp.93-99
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• 2011

This study surveyed the prevalence of traumatic reticular diseases (TRD) of slaughter cattle in Korea, the typology of the causative foreign bodies and the effects on beef quality and carcass weight. The overall prevalence of TRD in 3,121 slaughter cattle was 5.5%. However, the prevalence was significantly higher in Korea indigenous cattle Hanwoo (5.8%, p < 0.05) and female cattle (20.75%, p < 0.001). The prevalence significantly increased in aged cattle (p < 0.001). Major lesions related to foreign bodies were reticulitis (96%) and peritonitis (86%). Most causative foreign bodies were made of iron including nails, wires, steel rods, screw nails, and syringe needles. Cattle affected with TRD produced significantly lower grade quality of beef compared to normal cattle (p < 0.0001), but TRD did not affect carcass weight. The data will be useful in the management of TRD, with the aim of increasing beef productivity in Korea.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.2
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• pp.47-53
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• 1991

Recrystallization behaviors of ordered and disordered structures in $Ll_2$ type $Ni_3Fe$ alloy were studied through hardness measurement and differential thermal analysis. When the disordered structure was isothermally aged at $480^{\circ}C$ below order-disorder transition temperature, the hardness of the structure was increased due to progressive ordering with increasing aging time. The hardness of the disordered structure was increased rapidly with increasing deformation degree up to 10%, and then gradually increased with further deformation degree. while the hardness of the ordered structure was increased rapidly with increasing deformation degree up to 10%, showing a constant hardness value up to 50% and gradually decreased with further deformation degree. The hardness of the ordered structure was higher than that of the disordered structure at all same deformation degrees. The recrystallization temperature of the ordered and disordered structures were decreased with increasing deformation degree. At the same deformation degrees, the recrystallization temperature of the ordered structure was lower than that of the desordered structure.

• Nuclear Engineering and Technology
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• v.49 no.5
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• pp.1109-1112
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• 2017

The precise prediction of radiation embrittlement of aged reactor pressure vessels (RPVs) is a prerequisite for the long-term operation of nuclear power plants beyond their original design life. The expiration of the operation licenses for Korean reactors the RPVs of which are made from SA533B-1 plates and welds is imminent. Korean regulatory rules have adopted the US Nuclear Regulatory Commission's transition temperature shift (TTS) models to the prediction of the embrittlement of Korean reactor pressure vessels. The applicability of the TTS model to predict the embrittlement of Korean RPVs made of SA533B-1 plates and welds was investigated in this study. It was concluded that the TTS model of 10 CFR 50.61a matched the trends of the radiation embrittlement in the SA533B-1 plates and welds better than did that of Regulatory Guide (RG) 1.99 Rev. 2. This is attributed to the fact that the prediction performance of 10 CFR 50.61a was enhanced by considering the difference in radiation embrittlement sensitivity among the different types of RPV materials.

• Journal of the Korean Society of Safety
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• v.33 no.6
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• pp.58-65
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• 2018

The life span of the porcelain insulator was made to be 30 years, but currently many of the 154kV NGK porcelain insulators using in Korea are found to have passed the production life. Accidents caused by aged mechanical breakdown can lead to disruption of power supply in some areas, large economic losses, and casualties. Therefore, ultrasonic method, which is one of the non - destructive test methods, is applied as a method for evaluating the integrity of porcelain insulators. In this study, the experiment on the interface of cap was conducted and the difference between the energy difference and the attenuation coefficient of the reflected wave was derived according to the interface state of the steel - cement. The results of this study are expected to be used as the basic data of the ultrasonic testing to evaluate the interface condition of the porcelain insulator cap.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.709-731
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• 2022

Loss of fracture resistance due to thermal aging degradation is a potential limiting factor affecting the long-term (80+ year) viability of nuclear reactors. To evaluate the effects of decades of aging in a practical time frame, accelerated aging must be employed prior to mechanical characterization. In this study, a variety of chemically and microstructurally diverse austenitic stainless steels were aged between 0 and 30,000 h at 290-400 ℃ to simulate 0-80+ years of operation. Over 600 static fracture tests were carried out between room temperature and 400 ℃. The results presented include selected J-R curves of each material as well as K_0.2mm fracture toughness values mapped against aging condition and ferrite content in order to display any trends related to those variables. Results regarding differences in processing, optimal ferrite content under light aging, and the relationship between test temperature and Mo content were observed. Overall, it was found that both the ferrite volume fraction and molybdenum content had significant effects on thermal degradation susceptibility. It was determined that materials with >25 vol% ferrite are unlikely to be viable for 80 years, particularly if they have high Mo contents (>2 wt%), while materials less than 15 vol% ferrite are viable regardless of Mo content.