• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.212-215
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• 2002

Interfacial evaluation and damage sensing of the carbon fiber/epoxy-amine terminated (AT)-polyetherimide (PEI) composites were performed using micromechanical test and electrical resistance measurement. As AT-PEI content increased, the fracture toughness of epoxy-AT-PEI matrix increased, and thus their interfacial shear strength (IFSS) was improved due to the improved toughness. After curing process, the changes in electrical resistance (ΔR) with increasing AT-PEI contents increased gradually because of the changes in thermal expansion coefficient (TEC) and thermal shrinkage of matrix. Matrix fracture toughness was correlated to the IFSS, residual stress and electrical resistance. The results obtained from the electrical resistance measurement during curing process, reversible stress/strain, and durability test were consistent with modified matrix toughness properties.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.5
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• pp.481-487
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• 2012

Recently, the construction of the small Al alloy ships is an increasing trend in viewpoint such as the disposal issue of a retired ship, the enhancement of environmental regulation and resources recycling etc. for FRP ships. However, Al alloy ship which can achieve high speed by light weight in marine environment is exposed to a problem on materials damage by cavitation-erosion which is generated by large impact pressure with the collapse of air bubbles due to cavitation. Consequently, in this study, water cavitation peening technology was applied in Al alloy for ship to enhance durability life by preventing cavitation damage. So, the water cavitaton peening application time that presented the excellent cavitation characteristic investigated. The weight-loss of 5456-H116, 5083-H321 and 5052-O Al alloy at the optimum water cavitation peening time were improved to 42.11 %, 50.0 % and 25.7 %, respectively.

• Journal of the Korean GEO-environmental Society
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• v.18 no.11
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• pp.35-40
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• 2017

The rearside of concrete lining of tunnels constructed in cold region might experience on freezing due to the low temperature. This causes damage of concrete lining resulting in adverse affect on the durability as well as integrity of tunnel structure by causing damage to the concrete lining. In order to prevent the rearside of tunnel lining from freeing, the temperature change inside the concrete lining was measured by attaching a heating element to the tunnel lining surface and generating heat for a certain period of time. A special freezing chamber was developed to conduct the experiments considering in-situ environment. The carbone nanotube (CNT) was used as a heating element in this study. The temperature distribution of the concrete lining was measured by applying the heat to the heating element. The effect of the outside temperature and heating duration were analyzed.

• Journal of the Korean Geotechnical Society
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• v.36 no.8
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• pp.35-47
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• 2020

For permanent anchors used for slope reinforcement, bearing capacity and durability should be secured during the period of use. However, according to recent domestic and foreign studies, phenomena such as tension fractures, damage to anchorages, deformation and damage to slope and reduction of residual load over time have been reported along the long-term behavior of the anchors. These problems are expected to increase in the future, which will inevitably lead to problems such as increasing maintenance costs and relevant facility collapse. It is necessary to improve maintenance procedures and methods of ground anchors more practically. In this study, the problems and limitations of domestic maintenance methods were analyzed by conducting a literature study, and the measurement data of load cells installed on the install ground anchors were analyzed to determine the change in the residual load with regard to the elapsed date of the anchors. Based on the results, the effect of the construction conditions of anchors and the soil compositions on the increase and decrease of load were identified.

• Journal of The Korea Institute of Healthcare Architecture
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• v.27 no.4
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• pp.41-50
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• 2021

Purpose: This study is aimed at the case of the cognitive health design pilot projects promoted by the Seoul Metropolitan Government since 2014 in terms of design to solve social problems in accordance with the aging population of our society. The purpose of this study is to analyze the maintenance and management of the projects and to suggest implications for the promotion and expansion of sustainable cognitive health design in the future. Method: It set the analysis frame by dividing management into maintenance-damage-demolition for the spatial types and spatial elements suggested in the Seoul Cognitive Health Guidelines. And it analyze the actual conditions of four pilot projects based on the field survey. Results: First, the ratio of damage and demolition was higher than maintenance. Second, designs and techniques with low durability were applied. Most of the cases where floor marks were applied to the external environment were lost or difficult to recognize, and their functions were limited due to storage of goods and parking of vehicles and motorcycles. Third, there was a large variation according to the type of residence. The project contents that can be applied to the low-rise residential area were also limited, and more elements were demolished than in the apartment type. Implications: First, it should limit project contents of space types and space elements that can be maintained even over time. Second, it should seek sustainable design and technical solutions. Third, it should seek alternatives to cognitive health design in low-rise residential areas where a large number of elderly people live.

• Journal of the Semiconductor & Display Technology
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• v.21 no.1
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• pp.148-154
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• 2022

As the 4th industrial age approaches, the demand for semiconductors is increasing enough to be used in all electronic devices. At the same time, semiconductor technology is also developing day by day, leading to ultraprecision and low power consumption. Semiconductors that keep getting smaller generate heat because the energy density increases, and the generated heat changes the shape of the semiconductor package, so it is important to manage. The temperature change is not only self-heating of the semiconductor package, but also heat generated by external damage. If the package is deformed, it is necessary to manage it because functional problems and performance degradation such as damage occur. The package burn in test in the post-process of semiconductor production is a process that tests the durability and function of the package in a high-temperature environment, and heat dissipation performance can be evaluated. In this paper, we intend to review a new material formulation that can improve the performance of the adapter, which is one of the parts of the test socket used in the burn-in test. It was confirmed what characteristics the basic base showed when polyamide, a high-molecular material, and alumina, which had high thermal conductivity, were mixed for each magnification. In this study, functional evaluation was also carried out by injecting an adapter, a part of the test socket, at the same time as the specimen was manufactured. Verification of stiffness such as tensile strength and flexural strength by mixing ratio, performance evaluation such as thermal conductivity, and manufacturing of a dummy device also confirmed warpage. As a result, it was confirmed that the thermal stability was excellent. Through this study, it is thought that it can be used as basic data for the development of materials for burn-in sockets in the future.

• Computers and Concrete
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• v.32 no.2
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• pp.119-138
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• 2023

Concrete carbonation is a prevalent phenomenon that leads to steel reinforcement corrosion in reinforced concrete (RC) structures, thereby decreasing their service life as well as durability. The process of carbonation results in a lower pH level of concrete, resulting in an acidic environment with a pH value below 12. This acidic environment initiates and accelerates the corrosion of steel reinforcement in concrete, rendering it more susceptible to damage and ultimately weakening the overall structural integrity of the RC system. Lower pH values might cause damage to the protective coating of steel, also known as the passive film, thus speeding up the process of corrosion. It is essential to estimate the carbonation factor to reduce the deterioration in concrete structures. A lot of work has gone into developing a carbonation model that is precise and efficient that takes both internal and external factors into account. This study presents an ML-based adaptive-neuro fuzzy inference system (ANFIS) approach to predict the carbonation depth of fly ash (FA)-based concrete structures. Cement content, FA, water-cement ratio, relative humidity, duration, and CO2 level have been used as input parameters to develop the ANFIS model. Six performance indices have been used for finding the accuracy of the developed model and two analytical models. The outcome of the ANFIS model has also been compared with the other models used in this study. The prediction results show that the ANFIS model outperforms analytical models with R-value, MAE, RMSE, and Nash-Sutcliffe efficiency index values of 0.9951, 0.7255 mm, 1.2346 mm, and 0.9957, respectively. Surface plots and sensitivity analysis have also been performed to identify the repercussion of individual features on the carbonation depth of FA-based concrete structures. The developed ANFIS-based model is simple, easy to use, and cost-effective with good accuracy as compared to existing models.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.16-22
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• 2023

In this study, a salt water immersion test was performed on concrete specimens simulating the concrete mix design of the nuclear power plant, and the correlation between the amount of chloride and the XRF component according to the depth of the concrete was analyzed. The amount of chloride on the surface of the nuclear power plant concrete increased slightly with increasing immersion time in salt water, but the amount of chloride in the depth of 5.5 mm or more showed a clear tendency to increase with increasing immersion time in salt water. As a result of analyzing the correlation between the amount of chloride in concrete and the XRF component, the concrete with 20% FA substitution compared with the OPC concrete showed a very high correlation between the composition ratio of Cl ions and the evaluation result of salt damage resistance by XRF component analysis. Accordingly, it was confirmed that chlorine ion analysis and salt damage resistance performance evaluation by XRF component analysis were possible through repeated data accumulation in the nuclear power plant concrete mix with 20% fly ash replacement.

• Computers and Concrete
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• v.33 no.4
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• pp.341-348
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• 2024

Ultra-high-performance concrete (UHPC) has received remarkable attentions in civil infrastructure due to its unique mechanical characteristics and durability. UHPC gains increasingly dominant in essential structural elements, while its unique properties pose challenges for traditional inspection methods, as damage may not always manifest visibly on the surface. As such, the need for robust inspection techniques for detecting cracks in UHPC members has become imperative as traditional methods often fall short in providing comprehensive and timely evaluations. In the era of artificial intelligence, computer vision has gained considerable interest as a powerful tool to enhance infrastructure condition assessment with image and video data collected from sensors, cameras, and unmanned aerial vehicles. This paper presents a computer vision-based approach employing deep learning to detect cracks in UHPC beams, with the aim of addressing the inherent limitations of traditional inspection methods. This work leverages computer vision to discern intricate patterns and anomalies. Particularly, a convolutional neural network architecture employing transfer learning is adopted to identify the presence of cracks in the beams. The proposed approach is evaluated with image data collected from full-scale experiments conducted on UHPC beams subjected to flexural and shear loadings. The results of this study indicate the applicability of computer vision and deep learning as intelligent methods to detect major and minor cracks and recognize various damage mechanisms in UHPC members with better efficiency compared to conventional monitoring methods. Findings from this work pave the way for the development of autonomous infrastructure health monitoring and condition assessment, ensuring early detection in response to evolving structural challenges. By leveraging computer vision, this paper contributes to usher in a new era of effectiveness in autonomous crack detection, enhancing the resilience and sustainability of UHPC civil infrastructure.

• Journal of Chest Surgery
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• v.30 no.7
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• pp.670-676
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• 1997

The structural failure of the glutaraldehyde-treated xenograft valves has been the primary concern about the limited durability as predicted from the begimling of clinical use, and long-term follow-up has shown a significant incidence of primary tissue failure(PTF) from both biological and mechanical reasons. Twenty-seven patients with the low-profile lonescu-Shiley valves explanted from mitral position for PTF(Group III) were studied on the patient characteristics and valve pathology, and the results were compared with the matched observations of the Haycock(Group I) and of the standard-profile lonesiu-Shiley valves(Group II). Patients were aged 16 to 56 years(mean, 38.0$\pm$ 11.0 years), and the size of the failed mitral bioprosthesis was 30.8$\pm$ 1.3 mm. The hemodynamic consequences were stenosis in 29.6%, insufficiency in 44.4%, mixed steno-insufficiency in 14.8%, together with normal function for the rest of patients of prophylactic re-replacement. Pathology revealed calcification with or without tissue damage in 63.0% and tissue damage with or without calcification in 58.l%, in contrast with the observations of predominant tissue damage(76.8%) over calcification in Group I and of calcification(76.1%) over tissue damage in group II. Although dystrophic calcification has long and repeatedly dealt with patient's young age as a determinant of valve durability, such a characteristic evidence was not reached even in patients with calcified valves. Moreover, the prolonged explantation p riods from the studied on the previous report suggested strongly yet possibly evolving destructive processes among the valves in the remaining patients, and awaits further follow-up. In conclusion, PTF of the xenograft valves seems to result from more complicated biologic and metabolic reasons as well as more complex mecharical factors than the reported, and newer generation prostheses, with tissue preservation with glutaraldehyde, do not likely to provide decisive improvement in the occurrence of structural failurebioprostheses is generally limited to the highly aged.