• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.695-700
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• 2010

Material properties of the lock plate, which covers the gas-turbine blade, are studied using ultrasonic guided waves. The lock plate is a crucial part of a gas-turbine power plant. The wave velocity and attenuation coefficient are measured to investigate the changes in the material properties under three heat-treatment conditions. Compared to the destructive mechanical tests, the material characterization of Inconel X-750 can be performed more efficiently and nondestructively by using ultrasonic guided waves; this characterization helps identify the changes occurring in its elastic moduli and Poisson's ratio under different heat-treatment conditions. The wave velocity and hardness of Inconel X-750 are proportional to each other. This nondestructive technique for the measurement of material properties can be widely used in various industries to avoid catastrophic failure. It is also expected that the guided-wave technique can be applied as a new cost- and time-saving inspection tool for longer and wider inspection ranges.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.196-201
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• 2003

When the structures are used in cold regions, the mechanical properties and dimension stability of the blade will be changed. The proposal of this study is to test the durability of the structures in cold regions. It is necessary to select the most comfortable materials and fabrication processes for more stable structures in cold regions. To select the most comfortable materials and processes, the static strength has to know through the tensile static tests at the severe condition as cold regions. First, the tensile static specimens made by RIM (Resin injection molding) process & vacuum bagging process with reinforcement materials and resin. Tensile static tests were carried out on three laminate lay-ups (carbon prepreg, carbon fiber dry fabric) at different test temperature($24^{\circ}C$, $-30^{\circ}C$), determining properties such as the mechanical strength, stiffness and strain to failure. At different test temperature, in order to test the tensile strengths of these specimens used the low temperature chamber. Next, the results of this test were compared with each other. Finally, the most comfortable materials and fabrication processes can select based on these results. The results show the changes in the static behavior of three laminate lay-ups at different test temperatures. At low temperatures, the static strengths are higher than the ones at room temperature.

• Journal of Digital Contents Society
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• v.16 no.5
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• pp.691-697
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• 2015

Supercomputers are used for many different areas including new product design of industries as well as state-of-the-art science and technology for large amount of computational needs. Tachyon is a 4th supercomputer built at KISTI that is a high-performance parallel computing system with 3,200 computing nodes and infrastructures. This system is currently about 10,000 users and over 170 organizations are used, the number of jobs they are performing work in batch type form through a scheduler. Also, this system logs lots of job scripts, execution environment, library, job status from the job submit to end. In this paper, we analyzed batch jobs information from Sun Grid Engine, that use as a scheduler in Tachyon system, and job executed information in Tachyon System. In particular, we distinguished the fail jobs from the all tasks that users perform and we analyzed the cause of failure. Among them, we can extracted some of jobs that can be regarded as normal jobs through the improvement in those works logged as all of fail jobs.

• Tribology and Lubricants
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• v.37 no.2
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• pp.48-53
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• 2021

Wind energy is considered as the most competitive energy source in terms of power generation cost and efficiency. The power train of the pitch drive for a wind turbine uses a 3-stage complex planetary gear system in being developed locally. A gear train of the pitch drive consists of an electric or hydraulic motor and a planetary decelerator, which optimizes the pitch angle of the blade for wind generators in response to the change in wind speed. However, it is prone to many problems, such as excessive repair costs in case of failure. Complex planetary gears are very important parts of a pitch drive system because of strength problem. When gears are designed for the power train of a pitch drive, it is necessary to analyze the fatigue strength of gears. While calculating the specifications of the complex planetary gears along with the bending and compressive stresses of the gears, it is necessary to analyze the fatigue strength of gears to obtain an optimal design of the complex planetary gears in terms of cost and reliability. In this study, the specifications of planetary gears are calculated using a self-developed gear design program. The actual gear bending and compressive stresses of the planetary gear system were analyzed using the Lewes and Hertz equation. Additionally, the calculated specifications of the complex planetary gears were verified by evaluating the results from the Stress - No. of cycles curves of gears.

• Design & Manufacturing
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• v.13 no.1
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• pp.61-67
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• 2019

The cooling unit of the industrial showcase consists of a compressor, a condenser and an evaporator. An axial fan is used to circulate the air to improve the efficiency of the heat exchanger. In the past, aluminum fans have been used, which have problems such as low performance, efficiency, high failure rate, and high noise. This study is to develop high performance, high efficiency plastic fan replacing aluminum fan. A major factor in determining the performance and noise of an axial fan is the angle and cross-sectional shape of the blade, which is suitable for raising the lift force, thereby controlling the vortex, which is the main cause of noise and performance degradation. In order to produce a high efficiency injection molded fan, it is necessary to develop a mold that minimizes the deformation of the injection process for the designed shape. In this study, we developed a high efficiency, low noise plastic injection fan with more than 11% performance improvement and noise reduction compared to conventional aluminum fan.

• Journal of Bio-Environment Control
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• v.28 no.4
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• pp.322-327
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• 2019

This study was conducted to improve the performance of automatic grafting robot using image recognition technique. The stem diameters of tomatoes and cucumber at the time of grafting were $2.5{\pm}0.3mm$ and $2.2{\pm}0.2mm$ for scions and $3.1{\pm}0.7mm$ and $3.6{\pm}0.3mm$ for rootstocks, respectively. The grafting failure was occurred when the different height between scions and rootstocks were over 4 mm and below 2 mm due to the small contact area of both cutting surface. Therefore, it was found that the height difference at the cutting surface of 3 mm is appropriate. This study also found that grafting failure was occurred when the stem diameters of both scions and rootstocks were thin. Therefore, it was suggested to use at least one stem with thicker than the average stem diameter. Field survey on the cutting angle of stems by hand were ranged from 13 to 55 degree for scions and 15 to 67 degree for rootstocks, respectively, which indicates that this could cause the grafting failure problem. However, the automatic grafting robot developed in this study rotates the seedlings 90 degree and then the stems are cut using a cutting blade. The control part of robot use all images taken from grafting process to determine the distance between a center of both ends of stem and a gripper center and then control the rotation angle of a gripper. Overall, this study found that The performance of automatic grafting robot using image recognition technique was superior with the grafting success rates of cucumber and tomato as $96{\pm}3.2%$ and $95{\pm}4%$, respectively.

• Composites Research
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• v.33 no.5
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• pp.275-281
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• 2020

The mechanical property related to lap shear strength of the joint structure between carbon fiber reinforced polymer (CFRP) composite and metal (Ni-Cr Alloy) under varying environmental conditions (temperature and humidity) was studied in order to apply to the aircraft fan blade. Room temperature dry (RTD), elevated temperature wet (ETW), and cold temperature dry (CTD) environmental conditions were chosen for investigation based on the flight conditions of aircraft. Lap shear strength tests were conducted according to ASTM Standard D3528 to evaluate the shear strength. The microstructure characteristic of failure zone was analyzed by SEM images to check the adhesive shear strength with the three environmental conditions. In comparison with shear strength for the RTD condition, the shear strength in the ETW condition was reduced by 72.8% while those for the CTD condition increased by 56.5%. The moisture absorption and high temperature in ETW condition strongly had an affect on mechanical property of adhesive, while cold temperature could enhance the adhesive shear strength due to the higher brittleness.