• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.129-140
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• 2007

A major purpose of this study is to develop a drainage system that can quickly drain water penetrated into pavement layers to mitigate pot holes which is one of the major distress types in bridge deck pavements. This system can be established by applying a thin drainage layer between waterproof and pavement layers. The most important elements for this system are the performance of waterproof layer and construction technique for the thin drainage layer. The porous asphalt mix with the maximum aggregate size of 10mm is first developed based on the porous asphalt mix design guide proposed by NCAT, and various physical and mechanical tests are performed to confirm that the porous mix satisfies all the specification requirements. In addition, a series of laboratory tests including low-temperature bending and bonding strength tests for the MMA(Methyl Methacrylate) type of waterproofing material. It is observed from the tests that the MMA material satisfies all the specification requirements. To evaluate the Reld performance of the drainage system, a field study has been conducted on a relatively small size bridge. The QC/QA tests are conducted on the both waterproofing and pavement materials. It has been found that the drainage system works well to drain the water penetrated into the pavement layers.

• Conservation Science in Museum
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• v.17
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• pp.85-100
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• 2016

The Bukji-ri Stone Pensive Bodhisattva of Bonghwa in the collection of Kyungpook National University Museum was transported to the National Museum of Korea for display in a special exhibition('Masterpieces of Early Buddhist Sculpture 100 BCE - 700 CE') and therefore underwent conservation ahead of the exhibition's start date. The stone sculpture had visibly encrusted surface dirt, granular disintegration and fissures upon arrival. Notably, a crack running obliquely across its lower half rendered the object unable to support its own weight without a pedestal, so one was created in order to maintain the sculpture in an upright position while on exhibition. The sculpture was further examined using a polarizing microscope and a stereoscopic microscope. SEM-EDS resulted in petrographic analysis of the stone's mineral composition and identification of its surface contaminants. Polarizing light microscopy confirmed biotite granite as the main mineral component of the object. Several urethane resins cast in round cross-sections were inserted into the newly made pedestal and stability tests were perform to measure the frictional force of the resins. An additional test was performed to compare urethane resin and epoxy resin, with results showing urethane to have a higher coefficient of friction. Utilizing a pedestal with urethane resin effectively ensured the stability of the Bukji-ri Stone Pensive Bodhisattva of Bonghwa during the aforementioned exhibition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.5
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• pp.375-380
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• 2017

This paper reports the results of an acceleration test to predict the contact-induced failure that could occur at the cylinder-to-hole joint for the fuel rod of a sodium-cooled fast reactor (SFR). To incorporate the fuel life of the SFR currently under development at KAERI (around 35,000 h), the acceleration test method of reliability engineering was adopted in this work. A finite element method was used to evaluate the flow-induced vibration frequency and amplitude for the test parameter values. Five specimens were tested. The failure criterion during the life of the SFR fuel was applied. The S-N curve of the HT-9, the material of concern, was used to obtain the acceleration factor. As a result, a test time of 16.5 h was obtained for each specimen. It was concluded that the $B_{0.004}$ life would be guaranteed for the SFR fuel rods with 99％ confidence if no failure was observed at any of the contact surfaces of the five specimens.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.581-586
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• 2018

Cast iron manhole lids cause environmental pollution during the manufacturing process, and the work environment is very poor. In addition, if the height of the manhole cover does not match the height of the road surface, it causes considerable inconvenience and safety problems. This study proposes a height - adjustable steel manhole cover that can replace cast iron manhole covers and easily match the road surface with the upper surface of the manhole cover. Structural analysis was performed to grasp the design variable of the structure of the manhole cover, satisfying the required quality performance. To fabricate a manhole cover that satisfies the required load capacity, the optimal design for the U-shaped reinforcement structure was made. The cylindrical shape of the height adjustment part and the low frame were formed by bending the steel sheet into a circular shape and then welding. Reinforcing bars were also made by bending a steel plate. The height adjustment groove was machined by a CNC milling machine. Four prototypes were fabricated and a load bearing test was carried out, and new manhole cover was made reflecting results of the test. In the load bearing test, there was no breakage of the welded part, and deformation occurred mainly at the contact area between the groove and gusset plate. Deformation of 1 to 2.7mm occurred due to a load of 450kN. On the other hand, after removing the load, there was almost no residual deformation, and the load bearing evaluation was judged to be satisfactory because the manhole cover could be disassembled and reassembled.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.32-38
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• 2020

Cargo train braking uses the pressure changes in the air braking pipe to operate the braking tightening and releasing service repeatedly. Air-braking release failure means partial braking caused by a failure of the variable load valve after the driver handling the brake release. This phenomenon causes wheel flaws while driving a wagon, resulting in wheel breakage or train derailment. This study developed the air-braking release failure proof valve considering the technical requirements of the railway operation corporations. In addition, a durability test of the valve was carried out using a braking performance simulator, and its operating performance was evaluated from the pneumatic history under cyclic braking conditions. The warranty life of this valve was assessed by performing 160,000 cycles of testing of 12 prototypes in accordance with the zero-failure test method, considering the number of braking cycles while driving the wagon. During the durability test, the pneumatic input time, output time, and release velocity were almost constant. The warranty life of this valve was 59,860 times the 95% confidence level, which means that it can be operated without trouble for four years when the valve is installed in the bogie of the wagon.

• International Journal of Highway Engineering
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• v.5 no.1 s.15
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• pp.11-18
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• 2003

Road roughness, as the key factor influencing not only drivers' ride quality and safety but also pavement deterioration, is one of the most important pavement performance indicator to be evaluated by users' subjective assessment. For this reason, a specific number of the pavement roughness has been adopted to monitor the condition of a road for pavement management systems and to evaluate the quality of newly constructed sections, however, none of the unified methodology was internationally accepted. In Korea highway network, road roughness has been used mainly to evaluate newly placed pavement by using 7.6m CP (California Profile meter) to calculate PrI (Profile Index). But this instrument is manually operated to measure road profiles by traffic closure and their interpretation depends on personal bias. Therefore, problems arisen from the manually operated instrument will be overcome by using the APL (Longitudinal Profile Analyzer) which can be operated in the speed of 80km per hour. A study was conducted to correlate the relation from both concrete and asphalt pavement between IRI (measured by APL) and PrI (measured by 7.6m CP). Test results showed that there was a good correlation between IRI and PrI.

• Composites Research
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• v.28 no.4
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• pp.219-225
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• 2015

Air spoiler, which can reduce the drag during operation, can be considered as a possible means to reduce carbon dioxide emission and to increase fuel efficiency. In this study, a composite air spoiler was designed and tested by static and repeated loads. The Green Water Pressure of 0.1 MPa a ship experiences during operation was perpendicularly applied to the air spoiler. Air spoiler was manufactured with sandwich panel which has glass fabric face and balsa core. Multiple sandwich panels were assembled to steel frame by bolt joint. The joint was designed to have bearing failure and examined by static and fatigue tests. Tests showed that the designed joint has enough margin of safety to endure joint failure. The developed sandwich panel to air spoiler is planned to be applied to a large scale commercial ship.

• Korean Journal of Construction Engineering and Management
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• v.19 no.4
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• pp.34-42
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• 2018

Apartment is a typical type of housing preferred by the majority of people. However, and defect disputes occur because various defects such as cracks, subsidence, breakage, water leakage, dew condensation and dropout are confirmed with numerous structures and finishing materials. From this point of view, this paper analyzes defect frequency and costs of each warranty period by work types, and estimates defect risks by using defect dispute cases. It examined about 5,337 defect items for 32 apartment over ten years old. In this paper, there are 10 types of work types and the warranty liability period is divided into 6 categories. Based on these categories, defect frequency and costs are investigated, and finally defect risk of the warranty liability period by work types confirmed. As a result of this analysis, it was found that defect risk in RC and finishing work is very high. Especially the RC work revealed that there is a high risk of trying from the third year onwards and it was found that the defect risk up to the second year is high in the finishing work. Due to aging of RC structure, the defect risk gradually increases, and finishing work initially cause defect disputes because of the housing environment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.513-519
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• 2019

Typically, contaminated sediments cause clogging of the drain pipe, which increases the residual water pressure in the drain pipe; this study constructed a system for improving drainage efficiency of tunnels by reducing physical and chemical obstructions through ultrasonic energy generated by a PVDF film. The developed hybrid drainage system utilized a PVDF material film fused with an existing drainage tunnel and maintenance system resulting in the ability to initialize the reverse piezoelectric effect, which was evaluated through an on site application. In order to investigate the maintenance performance of the tunnel drainage system, contaminated sediments were simulated in a drainage pipe to test the effect of ultrasonic conditions on drainage efficiency in the laboratory. As a result of applying the developed portable equipment, the ultrasonic energy was generated for about 20 minutes resulting in a reduction of 74.62% of the contaminated sediments and improving drainage efficiency. From the tunnel, acoustic pressure measurements were taken to calculate the response rate while taking into account the laboratory results. In addition, PVDF film was attached to the transverse and longitudinal side of the drainage pipes where contaminated sediments occur most often in the field tunnel. these calculations show contaminant removal was 90% effective.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.2
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• pp.113-119
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• 2022

In order to improve the mechanical reliability of next-generation electronic devices including flexible, wearable devices, a high level of mechanical reliability is required at various flexible joints. Organic adhesive materials such as epoxy for bonding existing polymer substrates inevitably have an increase in the thickness of the joint and involve problems of thermodynamic damage due to repeated deformation and high temperature hardening. Therefore, it is required to develop a low-temperature bonding process to minimize the thickness of the joint and prevent thermal damage for flexible bonding. This study developed flexible laser transmission welding (f-LTW) that allows bonding of flexible substrates with flexibility, robustness, and low thermal damage. Carbon nanotube (CNT) is thin-film coated on a flexible substrate to reduce the thickness of the joint, and a local melt bonding process on the surface of a polymer substrate by heating a CNT dispersion beam laser has been developed. The laser process conditions were constructed to minimize the thermal damage of the substrate and the mechanism of forming a CNT junction with the polymer substrate. In addition, lap shear adhesion test, peel test, and repeated bending experiment were conducted to evaluate the strength and flexibility of the flexible bonding joint.