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김현수(Huynsoo Kim),도재윤(Jeyoon Do),강창룡(Changyong Kang),남기우(Kiwoo Nam) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.8
Demand of new nondestructive evaluations is growing for detecting fatigue crack growth behavior to predict long term performance of materials and structure in aggressive environments, especially when they are in a non-visible area. The acoustic emission technique is well suited to these problem and has drawn a keen interest because of its dynamic detection; extreme sensitivity and location of growing defects. This study has been to explain the effect of sub-zero treatment on the mechanical, fatigue and acoustic emission properties of austemped ductile cast iron by changing austemering from ductile cast iron. The results obtained from this study are summarized as follow; When the temperature of sub-zero treatment gets lower, much more retained austenite is transformed into martensite, which cause the increase in strength. Fatigue life and fatigue crack propagation property were almost same according to water quenching and sub-zero treatment in all specimens. It could be classified that main frequency range were generated by fatigue crack propagation (300㎑) and of cleavage and graphite fracture mechanism(600㎑).
남기우 한국비파괴검사학회 2003 한국비파괴검사학회지 Vol.23 No.3
본 연구에서는 식물에 나타나는 다양한 환경변화를 고려하여, 식물의 상태를 비파괴적인 방법으로 검토하여 식물생장을 제어하기 위한 기초적인 실험을 실시하였다. 건조토양에서 겉씨식물과 속씨식물은 물관부에서 발생하는 캐비테이션 신호만 검출되었다. 증류수를 공급한 직후는 물관부의 강한 신호와 원형질 연락사 및 세포막의 약한 신호가 동시에 검출되었다. 그러나 강산성수를 공급한 경우는 증류수를 공급한 경우와 상반되는 신호가 검출되었다. 바람의 세기, 잎의 수, 음악, 기온 및 습도는 음향 신호 발생 수에는 영향을 끼쳤으나, 검출된 신호의 주파수 범위는 같았다. A basic experiment was performed to control the plant growth using acoustic emission technique considering the environmental conditions for plant. At a dry soil condition, the signals due to the cavitation from xylem of angiosperm and gymnosperm were mainly detected. The strong signal from xylem and the weak signal from plasmodesmata and casparian strip were detected at the same time after distilled water was provided. Two signals after providing the acid and distilled water were contrary to each other. The wind, number of leaf, music temperature and humidity affected the acoustic emission count from plants but the frequency ranges of the detected signals were the same.