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Al6061-T6 평판 시편의 노치반경과 두께가 파괴 메커니즘에 미치는 영향
두샤오(Xiao Du),왕량(Liang Wang),최낙삼(Nak-Sam Choi) 대한기계학회 2021 大韓機械學會論文集A Vol.45 No.3
Al6061-T6 합금의 연성파괴는 네킹의 발생 시에 생기는 삼축인장응력과 관계가 있다. 노치 반경과 두께에 따른 시편 표피와 내부의 응력상태가 달라진다. 본 연구에서는 두께 4 mm, 8 mm의 평판으로 노치 없는 시편(un-notched), 노치 반경이 큰 시편(L-notched, R228.1 mm), 노치 반경이 작은 시편(S-notched, R2.5 mm)을 제작하였다. 슬립라인 이론(slip line theory), 타원기준(ellipse criterion), 유한요소법(FEM), 2D 디지털 이미지 상관법(2D-DIC)을 이용하여 노치 반경과 두께에 따른 응력상태와 파괴위치를 해석하였으며 주사 전자현미경(SEM) 관찰을 병행하여 파괴 양상을 관찰하였다. 노치반경이 작을수록 응력집중으로 인해 시편 내부에 형성한 높은 삼축인장응력이 파괴를 주도하였다. 두께가 커지면 파괴는 삼축인장응력과 최대전단응력에 의한 혼합모드의 파괴거동을 보였다. The fracture behavior of Al6061-T6 alloy is related to stress triaxiality formation during the local necking process of the specimen. Distribution of triaxial tensile stress varies with different notch radii and specimen thickness. In this study, plate specimens (un-notched), specimens with large notch radius (L-notched, R228.1 mm), and specimens with small notch radius (S-notched, R2.5 mm) were made of aluminum alloy plates (thickness 4 mm, 8 mm). Slip line theory, the ellipse criterion, finite element method (FEM), and 2D digital image correlation (2D-DIC) were used to find the effect of notch radii and specimen thickness on stress state distributions and initial fracture mechanisms. A scanning electron microscope (SEM) was used to observe the initial fracture surface. For a small notch radius causing high stress concentration, the fracture began at a site close to the notch tip due to high triaxial tensile stress. With increasing specimen thickness, the fracture surface showed a mixed mode failure behavior caused by both the triaxial tensile stress and maximum shear stress.
노치 반경과 재료 강도에 따른 고강도강 SENT 시편의 균열 개시 위치 분석
김재윤(Jae-Yoon Kim),황진하(Jin-Ha Hwang),김윤재(Yun-Jae Kim),마사키 오미야(Masaki Omiya) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
The Sheet Metal Forming process is important in manufacturing a car body. Cracking defects are one of the serious problems that reduce quality in sheet metal forming process. In this study, the effect of notch radius and material strength of the Single Edge Notched Tension (SENT) specimen on the crack initiation location of the high-strength steel was analyzed. Through the SENT experiment, it was confirmed that the crack initiation locations were different at the notch radius of 0.5mm and 5mm. Also, the crack initiation occurred at the back of the crack tip as the material strength increased. The experiment was simulated by Finite Element Analysis. The Stress Field according to the distance from crack tip was compared and analyzed. In this study, by introducing damage criterion, we were able to simulate the difference in crack initiation locations depending on the notch radius and material strength.
원형 노치 CT 시편을 이용한 다양한 피로수명평가 절차의 보수성 평가
강주연,장동주,허남수,김준영,김상언,이종민,김종성,김진원,김윤재,김대수 한국압력기기공학회 2019 한국압력기기공학회 논문집 Vol.15 No.2
In this study, to evaluate conservatism of various fatigue life evaluation procedures, fatigue tests were conducted using compact tension (CT) specimens with a round notch, made of A516 Gr.70 carbon steel and A240 TP304 stainless steel, under load-controlled cyclic condition. Experimental fatigue failure cycles were measured and compared with predicted fatigue lives using two different life evaluation methods; (1) Design-By-Analysis (DBA) procedure given in ASME B&PV Code, Sec. III, Div. 1, Subsec. NB-3200 and (2) structural stress-based approach provided in ASME B&PV Code, Sec. VIII, Div. 2, Part 5. To predict fatigue failure cycles, three-dimensional elastic finite element analysis was conducted. Fatigue lives were predicted by both design fatigue curve given in ASME B&PV Code, Sec. III, Div. 1, Appendices and best-fit fatigue curve suggested in NUREG/CR-6815 for the DBA procedure. Finally, fatigue lives evaluated by various methods were compared with test results, and then conservatism between each evaluation procedure was discussed.
구조응력기반 마스터 S-N 선도를 이용한 노치를 가지는 Al 7075 시편의 피로수명예측
곽시영(Si Young Kwak),황성철(Seong Chul Hwang),홍정균(Jeong Kyun Hong) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.2
본 논문에서는 임의의 응력 집중 계수를 갖는 일반 노치 구조물에 대한 마스터 S-N 선도를 이용한 피로 수명 예측 방법을 제안한다. 먼저 미국의 바텔 연구소에서 수행한 알루미늄 7075 노치 시험편(Kt = 1.5, 2, 4, 5)에 대한 피로 수명 데이터를 이용하여 구조응력을 계산하고 이에 기초한 마스터 S-N 선도를 작성하였다. 그 후 작성된 마스터 선도에서 유도된 예측 값과 Kt 3의 노치 시편에 대해 새롭게 실시한 피로 시험 결과를 비교하였다. 이러한 과정을 통해 결과적으로 구조응력 기반 마스터 S-N 선도의 피로 수명 예측의 정확성과 유용성을 검증하였다. This paper proposes the possibility of fatigue life estimation using the master S-N curve of a general notched structure with arbitrary stress concentration factor. Firstly, the structure stress was computed from the fatigue data that had been generated by Battelle Institute for Al 7075-T6 notched specimens (Kt=1.5, 2, 4, 5), and a master S-N curve based on the structural stress was drawn up. Secondly, a novel fatigue test was conducted for a notched specimen (Kt=3) and the result of this test was compared to the predictive value derived from the master S-N curve. From these processes, it was possible to validate the accuracy and usefulness of fatigue life estimation using master S-N curve.
배홍수,우경식,조형순,노진호,이수용 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.4
본 논문에서는 필수파괴에너지 실험을 통하여 얇은 연성 폴리메 멤브레인의 파괴에너지를 구하였다. 폴리머 재료로는 캡톤과 마일라를 고려하였으며 다양한 크기의 리가멘트 길이를 가지는 양단노치 인장시편을 제작하여 인장실험을 수행한 수 실험에서 구한 하중-변위선도에서 필수파괴에너지를 추출하였다. 각각의 재료에 대해 두 세트의 시편크기에 실험을 수행하고 그 결과를 비교하였다. In this study, fracture energy of thin ductile polymer membranes was obtained by essential work of fracture experiments. Double-edge notched tensile specimens with various ligament lengths were made for Kapton polyimide and Mylar (polyethylene terephthalate) films. Uniaxial tensile tests were performed and the energy was calculated from the load-displacement curves, from which the specific work of fracture was calculated. The experiments were performed for two sets of specimens with different length and width dimensions and the results were compared.
이준규,배홍수,우경식,노진호 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.4
본 논문에서는 얇은 연성 폴리머 멤브레인의 찢김 해석을 수행하였다. 해석 형상은 양 끝단에 인장력이 가해진 캡톤 폴리머를 양단 노치 시편을 고려하였으며, 균열 진전은 응집영역 모델링을 통하여 모사하였다. 상용유한요소 코드 ABAQUS를 사용하여 해석을 수행하였으며, 해석을 통하여 하중-변위선도를 중심으로 얇은 멤브레인의 찢김 거동을 조사하였다. 실험 결과와 비교하여 해석의 타당성을 검증하였다. In this paper, tearing analysis of thin ductile polymer membrane was performed. Double-edge notched tensile specimen was modeled with regular finite elements, and then a line of cohesive elements were inserted between the bulk elements along the expected tear line. The analysis results were compared with the experimental results. The load-displacement curves were carefully examined to investigate the tearing behavior of ductile thin polymer membranes.
STS304강의 순수 및 외팔보형 굽힘피로에 대한 파괴확률특성
노성국,정순억 경상대학교 해양산업연구소 2002 해양산업연구소보 Vol.15 No.-
Big accidents of flyings, vessel, subways, gas equipments, buildings and bridge happens frenquently. Therefore many people are suffering harm of property. The destruction cause of macaine components is almost accused by fatigue. This study is test for STS304 specimen by using pure and cantilever bending state. Rounded specimen and notched specimen including fracture surface investigation was comparatively experimented, fatigue life according to degree of surface finishing was examined. Fatigue fracture probability of notched canilever specimens were predicted by P-S-N curve, median rank and Weibull distribution. And at the relation with the rotational speed and stress the fatigue life of the test specimen was higher than low speed at high speed.