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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.
구조용 용접강 SWS 490B 의 피로균열 진전시 음향방출 거동
정중채(Jung-Chae Jeong),윤동진(Dong-Jin Yoon),박휘립(Philip Park),김기복(Ki-Bok Kim),이승석(Seung-Seok Lee) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
The objective of this study was to investigate the effect of AE activities during fatigue test.<br/> Laboratory experiment was carried out to identify AE characteristics of fatigue cracks for compact<br/> tension specimen. Compact tension specimen of SWS 490B was prepared for fatigue test. The<br/> relationship between a stress intensity factor and AE signals activity as well as conventional AE<br/> parameter analysis was discussed. From the experimental results, the features of specific parameters<br/> such as the length of crack growth, the AE energy and the AE peak amplitude, showed the almost<br/> same trend in their increase as the stress intensity factor increased. The fracture surface of test<br/> specimens revealed both intergranular fracture and transgranular fracture. Size and density of slip<br/> band by fatigue crack propagation were varied as the stress intensity factor increased, AE activities<br/> were different according to the slip band shape.
가공송전선용 초 내열 알루미늄 합금의 Drawing 거동에 관한 연구
鄭中采,辛奉文 한밭대학교 산업과학기술연구소 2001 논문집 Vol.5 No.-
STAL(Super Thermal Aluminum Alloy) containing Zr for overhead transmission line records good conductivity and thermal-resistance and has 2.6 times higher current carrying capacity than the usual ACSR at 230 ℃ with almost same sag property. Hence, we pursued a series of experiment to confirm the best drawing condition for STAL. In the case of changing the drawing speed from 200 to 500 m/min, grain size was generally decreased. Also, it was found that the tensile strength and conductivity decreased with increasing the drawing speed. So, it was concluded that the most suitable drawing speed is 400 m/min. As the final wire diameter decreased, tensile strength increased. However 4.5 ㎜ of diameter recorded the highest tensile strength. After tensile test, the cross section is almost crater type of ductile fracture, but partially showed fish-mouth and chevron type of brittle fracture.
피로균열 열림 및 닫힘에 따른 음향방출 신호 발생 특성 고찰
정중채(Jung-Chae Jeong),윤동진(Dong-Jin Yoon),박휘립(Philip Park),김기복(Ki-Bok Kim),이승석(Seung-Seok Lee) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
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 SWS 4908 and Al 7075-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 at the time of early stage of crack opening and closure, whereas a few in the peak loading of cycle. Also the time of high occurrence of AE event was different with each specimen. However, in the same material, the trend of AE activity was not affected by the change of cyclic frequency (0.1, 0.2, 1 ㎐). It was found that AE activities during crack opening and closure depend on material properties such as micro-structure, yield strength and elongation.
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.
정중채 세계기독교통일신령협회 2004 統一世界 Vol.- No.5
오늘날 기독교회가 안고 있는 신학적 교리 문제에 대하여 신앙적 양심으로 고백하고자 한다. 하나님의 섭리는 시대에 따라 때로는 기존 교리에 상반되는 말씀과 진리를 선지자를 통하여 선포하신다.
SWS 490B 강의 피로균열 진전시 음향방출 거동과 파단면 관계
鄭中采,尹東珍,朴徽立,金基福,李承錫 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.8
The objective of this study was to investigate the effect of AE activities during fatigue test. Laboratory experiment was carried out to identify AE characteristics of fatigue cracks for compact tension specimen. The relationship between a stress intensity factor and AE signals activity was discussed. From the experimental results, the features of specific parameters such as the length of crack growth, the AE energy and the AE peak amplitude, showed similar trend in their increase as the stress intensity factor increased. The fracture surface of test specimens revealed both intergranular fracture and transgranular fracture. Size and density of slip band were varied as the stress intensity factor increased and AE activities were different according to the slip band shape.