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구조용 알루미늄 합금에서의 피로균열 열림 및 닫힘 시 AE 발생특성 연구
정중채,윤동진,박휘립,김기복,이승석 한국비파괴검사학회 2002 한국비파괴검사학회지 Vol.22 No.2
피로균열 진전시 균열 열림 및 닫힘에 따른 음향방출 특성을 규명하고자 구조용 알루미늄 2024- T4와 6061-T6재료에 대해 소형인장 시편에서의 피로균열 진전시 발생되는 AE특성을 관찰하였으며, 기존의 AE 파라미터 분석은 물론 재료의 파단면 분석을 통해 재료특성에 따른 AE 발생거동 사이의 관계를 논의 하였다. 대부분의 음향방출 신호는 균열이 열리기 시작하는 위상과 균열이 완전히 닫히는 위상에서 많이 발생되었으며 하중을 최대로 받는 균열 완전 열림에서는 전반적으로 적게 발생됨을 알 수 있었다. 또한 재료에 따라서 균열 완전 열림 부분에서 발생하는 음향방출 특성은 달라졌으나 각 피로 사이클 주파수 변화(0.1, 0.2, 1.0Hz)에 따른 결과에서는 동일 재료일 경우 피고 사이클 주파수가 변화하더라도 각 사이클에서의 AE hit 발생 경향은 비슷하게 나타났다. 이와 같은 결과로부터 균열 열림 및 닫힘시 재료의 미세조직과 기계적 특성인 인장강도와 항복강도에 따라 AE 특성이 달리질 수 있음을 알 수 있었다. The objective of this study was to investigate the effect of crack opening and closure in the AE activities during fatigue test. Laboratory experiment using various materials and test conditions were carried out to identify AE characteristics of fatigue crack propagation. Compact tension specimens of 2024 T4 and 6061 T6 aluminum alloy were prepared for fatigue test. AE activities were analyzed based on the phase of the loading cycle. Generally, most of AE were generated when the crack begins opening and the crack closes fully, whereas a few in the pull opening of the crack. Also AE activity in the peak loading of cycle was different with each specimen. However, in the same material, AE activity was not affected by the change of cyclic frequency (0.1, 0.2, 1.0Hz). It was found that AE activities during crack opening and closure depend on material properties such as micro-structure, tensile strength and yield strength.
연소합성법에 의한 SiC 분말의 제조 시 반응변수 연구
정중채,신봉문 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.6
Silicon carbide was synthesized by a combustion synthesis process using exothermic mixture of Mg and (-C₂F₄-) as an activated additive, silicon and carbon. Silicon carbide was synthesized differently with the addition of the activated additive. Especially, with 25wt.% of the additive, better conversion of Si to SiC was obtained. For the types of carbon, it was observed that carbon black and activated carbon showed better reactivity than graphite. In regard of the molar ratio change, when the molar ratio of silicon vs. carbon was 1:2, Si was converted to silicon carbide completely. Among the products, MgF₂ was entirely removed by leaching for 4hrs. at a mixture of 10vol.%(HNO₃+HF)+90% water.
TiO$_2$/Mg 반응에 의한 흑색산화티타늄 제조시 반응 변수 연구
정중채,조정웅,이혁희,이종현,원창환,Jeong, Jung-Chae,Jo, Jeong-Ung,Lee, Hyeok-Hui,Lee, Jong-Hyeon,Won, Chang-Hwan 한국재료학회 2001 한국재료학회지 Vol.11 No.10
One of the important phase of black titanium oxide is $Ti_4O_7$</TEC> which has the excellent properties such as the greatest electrical conductivity among the titanium oxides, chemical resistance against acidic and alkalic conditions and electro-wave absorption etc., so it has been considered as a promising material to be used widely all over the parts of industries. In this study, $Ti_4O_7$</TEC> phase was successfully synthesized by the reaction of TiO$_2$/ Mg system. With the change of the mole of TiO$_2$to Mg, the most excellent blackness was appeared in the 3.5 mole which was the smaller amount than the stoichiometric 4.0 mole. In addition, we found that the blackness decreased as the mole ratio of reactent increased. With decreasing particle size of magnesium, blackness of titanium oxide increased. The reaction property was changed with the compaction pressure, and optimum pressure was found to be 10 MPa. At 55$0^{\circ}C$ of reduction temperature, the blackness increased as the reaction time increased. The blackness of synthesized black titanium oxide was 14 to 18, and the average particle size was 0.2 $\mu\textrm{m}$.