• 동력기계공학회지
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• 제16권1호
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• pp.58-64
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• 2012

Power plant boiler is one of the most important utilities providing steam to turbine in thermal power plant. It is composed of thousands of boiler tubes for high efficient heat transfer. Boiler tube material is used in such high temperature and pressure as $540^{\circ}C$, $170kg/mm^2$. The boiler tube material is needed to resist corrosion damage, creep damage and fatigue damage. 2.25%Cr-1Mo steel is used for conventional boiler tubes. In these days steam temperature and pressure of the power plant became higher for high plant efficiency. So, the material property of boiler tube must be upgraded to meet the plant property. Several boiler tube material was developed to meet such condition. X20CrMoV12.1 steel is also developed in early 1980's and used for superheater and reheater tubes in supercritical boilers. The material has martensitic structure, which is difficult to evaluate the material degradation. Boiler tube material at severe condition was tested to evaluate long term and short term degradation and creep. Through long term and high temperature degradation test, lath structure was decreased and recrystallization has been proceeded by sub-crystal. And in this research the effect of temperature and stress on boiler tube characteristic,for example, deformation by creep was changed rapidly at relatively high temperature and stress because creep was affected easily by temperature and stress.

• 한국도로학회논문집
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• 제19권5호
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• pp.107-115
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• 2017

PURPOSES : The piezoelectric energy road analysis technology using a three-dimensional finite element method was developed to investigate pavement behaviors when piezoelectric energy harvesters and a new polyurethane surface layer were installed in field conditions. The main purpose of this study is to predict the long-term performance of the piezoelectric energy road through the proposed analytical steps. METHODS : To predict the stresses and strains of the piezoelectric energy road, the developed energy harvesters were embedded into the polyurethane surface layer (50 mm from the top surface). The typical type of triaxial dump truck loading was applied to the top of each energy harvester. In this paper, a general purpose finite element analysis program called ABAQUS was used and it was assumed that a harvester is installed in the cross section of a typical asphalt pavement structure. RESULTS : The maximum tensile stress of the polyurethane surface layer in the initial fatigue model occurred up to 0.035 MPa in the transverse direction when the truck tire load was loaded on the top of each harvester. The maximum tensile stresses were 0.025 MPa in the intermediate fatigue model and 0.013 MPa in the final fatigue model, which were 72% and 37% lower than that of the initial stage model, respectively. CONCLUSIONS : The main critical damage locations can be estimated between the base layer and the surface layer. If the crack propagates, bottom-up cracking from the base layer is the main cracking pattern where the tensile stress is higher than in other locations. It is also considered that the possibility of cracking in the top-down direction at the edge of energy harvester is more likely to occur because the material strength of the energy harvester is much higher and plays a role in the supporting points. In terms of long-term performance, all tensile stresses in the energy harvester and polyurethane layer are less than 1% of the maximum tensile strength and the possibility of fatigue damage was very low. Since the harvester is embedded in the surface layer of the polyurethane, which has higher tensile strength and toughness, it can assure a good, long-term performance.

• 한국지반공학회논문집
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• 제36권8호
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• pp.35-47
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• 2020

비탈면 보강 용도로 사용되는 영구앵커의 경우 사용기간 동안 지지력 및 내구성이 확보되어야 한다. 그러나 최근 국내·외 연구 결과에 따르면 앵커의 장기거동에 따라 긴장재 파단, 정착구 파손, 비탈면 변형 및 손상, 시간에 따른 잔존긴장력 감소 등의 현상들이 보고되고 있다. 이러한 문제는 앞으로 증가할 것으로 보이며, 이로 인한 유지보수 비용의 증가, 시설물 붕괴 사고 등의 문제가 불가피할 것으로 보인다. 이에 본 연구에서는 그라운드 앵커의 유지관리 절차 및 방법을 현실적으로 보완하기 위해 문헌연구를 수행하여 국내 유지관리 기법의 문제점 및 한계를 제시하였다. 이후 실제 현장 그라운드 앵커에 설치되어 있는 하중계 계측자료를 분석하여 앵커들의 경과일에 따른 잔존긴장력의 변화를 파악하였고, 최종 분석 결과를 통해 앵커의 시공조건, 구성암반 등이 긴장력의 증감에 미치는 영향을 파악하였다.

• 한국프랜차이즈경영연구
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• 제12권2호
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• pp.35-49
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• 2021

Purpose: The major objective of this study is to develop a model for the impact of franchisors' Gapjil (verbal·nonverbal Gapjil, abusing bargaining position, refusing transaction, false or exaggerated information, restrictive practices, unfair damage compensation) on franchisee's recontract intention. We also examine the mediating role of economic satisfaction and social satisfaction in the relationship between franchisors' Gapjil and franchisee's contract intention. Research design, data, and methodology: Data were collected from franchisee owners located nationwide in Korea. Out of 256 questionaires distributed, a total of 256 questionnaires were returned. After excluding 10 invalid respondent questionnaires, we coded and analyzed 246 valid questionnaires (effective response rate of 96.09%) using frequency, confirmatory factor analysis, correlations analysis, and structural equation modeling with SPSS 22.O and SmartPLS 3.0. Results: The findings of this study are summarized as follows: First, among the Gapjil of the franchisors, restrictive practices and unfair damage compensation had negative effects on economic and social satisfaction, but verbal and nonverbal Gapjil for economic and social satisfaction was not significant. Second, abusing bargaining positions and false or exaggerated information had negative effects on social satisfaction, but for economic satisfaction, found to be insignificant. Third, economic and social satisfaction had positive effects on the franchisee's recontract intention to the franchisor. Conclusion: The following implications of this study are as follows. First, the construct of Gapjil that occurs between the franchisors and the franchisees was first presented, and the franchisors' Gapjil is divided into interpersonal Gapjil and structural Gapjil. Second, the Gapjil of the franchisors can be an important predictor variable in maintaining and developing a long-term relationship between the franchisors and the franchisees. Third, solving conflict due to the Gapjil problem between franchisors and franchisees can be an important factor for franchisors and franchisees to co-survive and thrive in Korean franchise system. Fourth, this study suggest that managing the Gapjil of the franchisors was a important antecedent factor in maintaining long-term relationship between the franchisors and the franchisees. Therefore, this study will help franchisors formulate effective symbiotic marketing strategies to satisfy relationships with franchisees and consequently enhance long-term orientation.

• 복합신소재구조학회 논문집
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• 제5권2호
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• pp.27-32
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• 2014

Since the collapse of historical masonry structures in Europe in the late 1990's, the interests in understanding the long-term effect of masonry under sustained compressive stresses have increased. That requires combining the significance of time-dependent effects of creep with the effect of damage due to overstress to realize the evolution of cracks and then failure in masonry. Meanwhile, composite analysis of masonry columns was proven effective for realizing ultimate strength capacity of masonry column. In this study, a simplified mechanical model with step-by-step in time analysis was proposed to incorporate the interaction of damage and creep to estimate the maximum stress occurred in masonry. It was examined that the interaction of creep and damage in masonry can accelerate the failure of masonry.

• Smart Structures and Systems
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• 제15권2호
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• pp.283-297
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• 2015

Jacket-type offshore structures are always exposed to severe environmental conditions such as salt, high speed of current, wave, and wind compared with other onshore structures. In spite of the importance of maintaining the structural integrity for an offshore structure, there are few cases to apply a structural health monitoring (SHM) system in practice. The impedance-based SHM is a kind of local SHM techniques and to date, numerous techniques and algorithms have been proposed for local SHM of real-scale structures. However, it still requires a significant challenge for practical applications to compensate unknown environmental effects and to extract only damage features from impedance signals. In this study, the impedance-based SHM was carried out on a 1/20-scaled model of an Uldolmok current power plant structure in Korea under changes in temperature and transverse loadings. Principal component analysis (PCA)-based approach was applied with a conventional damage index to eliminate environmental changes by removing principal components sensitive to them. Experimental results showed that the proposed approach is an effective tool for long-term SHM under significant environmental changes.

• 열처리공학회지
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• 제7권3호
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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.

• Geomechanics and Engineering
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• 제9권4호
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• pp.499-511
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• 2015

The creep property of salt rock significantly influences the long-term stability of the salt rock underground storage. Triaxial creep tests were performed to investigate the creep behavior of salt rock. The test results indicate that the creep of salt rock has a nonlinear characteristic, which is related to stress level and creep time. The higher the stress level, the longer the creep time, the more obvious the nonlinear characteristic will be. The elastic modulus of salt rock decreases with the prolonged creep time, which shows that the creep damage is produced for the gradual expansion of internal cracks, defects, etc., causing degradation of mechanical properties; meanwhile, the creep rate of salt rock also decreases with the prolonged creep time in the primary creep stage, which indicates that the mechanical properties of salt rock are hardened and strengthened. That is to say, damage and hardening exist simultaneously during the creep of salt rock. Both the damage effect and the hardening effect are considered, an improved Maxwell creep model is proposed by connecting an elastic body softened over time with a viscosity body hardened over time in series, and the creep equation of which is deduced. Creep test data of salt rock are used to evaluate the reasonability and applicability of the improved Maxwell model. The fitting curves are in excellent agreement with the creep test data, and compared with the classical Burgers model, the improved Maxwell model is able to precisely predict the long-term creep deformation of salt rock, illustrating our model can perfectly describe the creep property of salt rock.

• 수산경영론집
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• 제54권2호
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• pp.045-058
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• 2023

This study aims to analyze the cost of climate change damages to laver and sea mustard aquaculture, which are considered to be highly vulnerable to climate change in Korea. For this purpose, the correlation between aquaculture production and climate factors such as water temperature, salinity, air temperature, and precipitation was estimated using a panel regression model. The SSP scenario was applied to predict the changes in production and damage costs due to changes in future climate factors. As a result of the analysis, laver production is predicted to decrease by 18.0-27.2% in 2050 and 20.6-61.6% in 2100, and damage costs are predicted to increase from 29.7-50.8 billion KRW in 2050 to 35.7-116.1 billion KRW in 2100. Sea mustard production is projected to decrease by 24.5-37.2% in 2050 and 24.0-34.5% in 2100, with similar damage costs of 41.1-61.8 billion KRW and 41.1-58.6 billion KRW, respectively. These damage costs are expected to occur in the short term as damage caused by fishery disasters such as high temperatures, and in the long term as a decrease in production due to changes in aquaculture sites. Therefore, measures such as strengthening the forecasting system to prevent high-temperature damage, developing high-temperature-resistant varieties, and relocating fishing grounds in response to changes in aquaculture sites will be necessary.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1248-1253
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• 2007

Urban transit or subway stations generally service for a long period of several decades. And, the urban transit or subway is public transportation which lots of people takes every day. During the service time, they are inevitably damaged from environmental corrosion, material aging, fatigue, and the coupling effects with long-term loads and extreme loads. The included damage accumulates and performance degenerates due to the above factors. They would inevitably reduce the resisting capacity of station against the disaster; even they result in collapse with the structural failure under extreme loads. And, if disaster such as earthquake, fire, etc. happens, it causes huge property damage and threatens the human lives. Because of these above reasons, the intelligent health surveillance system should be researched and developed for ensuring the safety of station. In this paper, the research plans of the intelligent health surveillance system of urban transit station are presented. And also, the development or establishment directions of this system are suggested.