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양유창(Yoo Chang Yang),한경섭(Kyung Seop Han) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
Optical fiber vibrations sensors (OFVSs) and extrinsic Fabry-Perot interferometer (EFPI) were used in<br/> damage monitoring of fiber-metal laminates(FML). The optical fiber vibration sensor and EFPI were applied<br/> in order to detect and evaluate the strain, damage and failure of FML. Damages in composites, such as matrix<br/> cracks, delamination and fiber breakage may occur as a result of excessive load, fatigue and low-velocity<br/> impacts. Tensile and indentation test was performed with the measurement of optical signal and acoustic<br/> emission (AE). The signals of the optical fiber vibration sensor due to damages were quantitatively evaluated<br/> by wavelet transform. It was found that damage information of comparable in quality to acoustic emission<br/> data could be obtained from the optical fiber vibration sensor signals.
오광환(Kwang-Hwan Oh),양유창(Yoo-Chang Yang),한경섭(Kyung-Seop Han) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8
The effects of short fiber and particle hybrid reinforcement on fatigue crack propagation behaviors in aluminum matrix composites have been investigated. Single and hybrid reinforced 6061 aluminum containing same 20 Al₂O₃ volume % with four different constituent ratios of short fibers and particles were prepared by squeeze casting method and tested to check the near-threshold and stable crack growth behavior. The fatigue threshold of the composites increased with portion of particle contents and shows the superior crack resistance in low stress intensity range. In stable crack growth region, the slop of Paris' Law which indicating the crack growth rate was independent of microstructure. After allowing for crack closure, the differences in crack propagation rate among the composites were significantly diminished. Observation of the crack path revealed that the fatigue crack propagate mainly to the interfaces and across the hoop direction of short fibers, however crack seldom propagate though the particle for their low aspect ratio. Overall experimental results was shown that Particle reinforcing was enhanced the fracture toughness and fatigue threshold and induced the resistance of crack propagation.
오광환(Kwang Hwan Oh),정창규(Chang Kyu Jung),양유창(Yoo Chang Yang),한경섭(Kyung Seop Han) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
Acoustic emission behavior during fatigue crack growth test was investigated under various loading<br/> condition. To describe the acoustic emission activity, counts rate (dh/dn) was related with SIFR (stress<br/> intensity factor range, DK). Results indicated that SIFR could be divided into two parts according to its<br/> relationship with counts rate. For DK<25MPa m , counts rate was increased as the SIFR increased. However,<br/> for values greater than 25MPa m , decreasing behavior was shown. This behavior of counts rate corresponding<br/> SIFR was keeping the same trend regardless of load range or crack length. Acoustic emission response to the<br/> single overload was sudden drop and slow recovery in counts rate like crack growth retardation. Under<br/> variable loading condition, counts rate of each loading block was same as that of constant amplitude loading.<br/> Overall experimental data was somewhat scattered since sensitive characteristics of acoustic emission method.<br/> However, these empirical relations indicated that counts rate was uniquely correlate with single parameter,<br/> SIFR.
PEMFC용 복합소재 분리판을 위한 2단계 제조공법의 제조 조건에 대한 연구
허성일(Heo, Seong-Il),오경석(Oh, Kyeong-Seok),윤진철(Yun, Jin-Cheol),양유창(Yang, Yoo-Chang),한경섭(Han, Kyung-Seop) 한국신재생에너지학회 2007 한국신재생에너지학회 학술대회논문집 Vol.2007 No.06
The 2-step manufacturing method consisting of preforming and stamping processes was developed to manufacture composite bipolar plates for PEMFCs. The preform was composed of expanded graphite, graphite flake and phenol resin. Precuring conditions were optimized by checking the electrical conductivity, flexural strength and microstructure. Precuring temperature (100?C) slightly above the melting point of phenol powders (90?C) induced moderate curing, but also prevented excessive curing. Preforms utilizing the tangled structure of expanded graphite were easily fabricated at low pressure of 0.07-0.28MPa. The proper precuring time, 5min, was determined to fabricate the preform stably because insufficient and excessive precuring deteriorated the flexural strength of composite bipolar plates.