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하영준(Young-Joon Ha),이승준(Seung-Joon Lee),이준현(Joon-Hyun Lee),변준형(Joon-Hyung Byun) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.6
Carbon fibre reinforced plastics (CFRP) should be inspected in fabrication process in order to enhance quality by prevent defects such as delamination and void. Generally, ultrasonic technique is widely used to evaluate FRP. In conventional ultrasonic technique, transducer should be contacted on FRP. However, conventional contacting method could not be applied in fabrication process and novel non-contact evaluating technique was required. Technique using air-coupled transducer can make non-contacting ultrasonic technique available in evaluation of FRP. Therefore, in this study, generation technique of laser-based ultrasound using Nd:YAG pulse laser(532㎚, 32mJ) system and reception technique using air-coupled transducer are applied for the non-destructive and non-contact evaluation of delamination in CFRP. Wave propagating through artificial delamination region was received using pitch-catch arrangement. Signal characteristics due to defects were analyzed to find a factor for detecting defects. PZT sensor was used to get a trend of waveform and fundamental database. The high frequency component of 1.1 ㎒ of laser-generated guided wave received with piezoelectric sensor disappeared after propagating through delamination region. However, it could not be received this high frequency guided wave by using air-coupled transducer and linear slit array. In a frequency spectrum of laser-generated guided wave received by air-coulped transducer, the first peak of frequency spectrum under 100㎑ received in the defect region showed higher than in the sound region. The peak of frequency spectrum represented approvable parameter to detect delamination in CFRP. By using this feature, line scanning data was acquired in fully non-contacting pitch-catch method and was proved as useful technique for detecting delamination in CFRP.
남자 중학생의 연속 구르기 동작과 체력과의 상관에 관한 연구
하영준 ( Ha Young-joon ) 인하대학교 교육연구소 1999 교육문화연구 Vol.5 No.-
The purpose of this study was to investigate the relationship between the records of six physical fitness factors and the records considering of the middle school boys' speed of forward and back rolling with bending knees, their distance score, and their conditions of physique. The 330 subjects of study were the random sampled boys at 'S' middle school in Inchon. The itemized measurement content was produced the speed of the consecutive 5 times and 7 times of forward and back rolling at first Secondary, I produced records considering of height, sitting height, and weight. It was measured back strength for strength, 1000m running for endurance, long jump for power, shuttle run for agility, straight walking test for balance, and trunk flexion for flexibility as six physical fitness factors. To make the measured data be meaningful, I wrote down the average of two measured records. I used Pearson Correlation that is lower ranking program of SPSSx to inspect significance among the measured items and I came to an conclusion as below. 1) It was divided into speed of consecutive 5 times and 7 times of forward and back tumbling with their height and the result showed the meaningful correlation coefficient in all six physical strength factors of strength, power, agility, balance, flexibility, and endurance. 2) It was divided into speed of consecutive 5 times of forward and back rolling with their sitting height and the result showed the meaningful correlation coefficient in all six physical fitness factors of strength, power, agility, balance, flexibility, and endurance. 3) There were partially meaningful correlation coefficient in the relation between the records produced in other 29 types of consecutive rolling with bending knees and measured data of six physical fitness factors.