탄소성 유한요소 해석을 통한 곡관 두께에 따른 파손 위치 및 균열 진전 방향 분석

김재윤,이종민,김윤재,김진원 한국압력기기공학회 2022 한국압력기기공학회 논문집 Vol.18 No.1

When piping system in a nuclear power plant is subjected to a beyond design seismic condition, it is important to accurately determine possibility of crack initiation and, if initiation occurs, its location and time. From recent experimental works on elbow pipes, it was found that the crack initiation location and crack propagation direction of the SA403 WP316 stainless steel elbow pipe were affected by the pipe thickness. In this paper, the crack initiation location and crack propagation direction for SA403 WP316 stainless steel elbow pipes with different thickness were analyzed via elastic-plastic finite element analysis. Based on FE results, the effect of the pipe thickness on different crack initiation location and crack propagation direction was analyzed using ovality, stress and strain components. It was also confirmed that the presence of internal pressure had no effect on the crack initiation location and crack propagation direction.

혼합모드 하중 하에서의 피로균열닫힘과 성장거동

송삼홍(Samhong Song),서기정(Kijeong Seo),이정무(Jeongmoo Lee) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

The stress conditions acting on the practical structure are complex, and thus most cracks existing in the practical structures are under mixed-mode loading conditions. The effect of shear load component of mixed-mode loading acts more greatly in the stage of crack initiation than crack propagation stage. Hence, research on the behavior in the stage of crack initiation need to be examined in order to evaluate behavior of mixed-mode fatigue cracks. In this study, the crack opening displacement(COD) was measured by using the direct measuring method(DMM). We examined the behavior at crack tip by determining crack opening load. From the test results, the propagation behavior of mixed-mode fatigue cracks was evaluated. Also, we examined the characteristic of crack propagation under mixed-mode loading by considering propagation directions and paths of mixed-mode fatigue cracks.

Peridynamic analysis of dynamic fracture behaviors in FGMs with different gradient directions

Miaomiao Kou,Jing Bi,Binhang Yuan,Yunteng Wang 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.3

In this article, a developed bond-based peridynamic model for functionally graded materials (FGMs) is proposed to simulate the dynamic fracture behaviors in FGMs. In the developed bond-based peridynamic model for FGMs, bonds are categorized into three different types, including transverse directionally peridynamic bond, gradient directionally peridynamic bond and arbitrary directionally peridynamic bond, according to the geometrical relationship between directions of peridynamic bonds and gradient bonds in FGMs. The peridynamic micromodulus in the gradient directionally and arbitrary directionally peridynamic bonds can be determined using the weighted projection method. Firstly, the standard bond-based peridynamic simulations of crack propagation and branching in the homogeneous PMMA plate are performed for validations, and the results are in good agreement with the previous experimental observations and the previous phase-field numerical results. Then, the numerical study of crack initiation, propagation and branching in FGMs are conducted using the developed bond-based peridynamic model, and the influence of gradient direction on the dynamic fracture behaviors, such as crack patterns and crack tip propagation speed, in FGMs is systematically studied. Finally, numerical results reveal that crack branching in FGMs under dynamic loading conditions is easier to occur as the gradient angle decreases, which is measured by the gradient direction and direction of the initial crack.

혼합모드(Ⅰ+Ⅱ)하에서 각도와 균열길이 변화를 갖는 피로균열 전파 거동

정의효,허방수,권윤기,오택열 韓國工作機械學會 2000 한국생산제조학회지 Vol.9 No.5

The applications of fracture mechanics have traditionally concentrated on cracks loaded by tensile stresses, and growing under an opening or mode I mechanism. However, many cases of failures occur from growth of cracks subjected to mixed mode loading. Several criteria have been proposed regarding the crack growth direction under mixed mode loadings. This paper is aimed at investigation of fatigue crack growth behaviour under mixed mode(I+II) with variation of angle and pre-crack length in two dimensional branched type precrack. Especially the direction of fatigue crack propagation was predict-ed and effective stress intensity factor was calculated by finite element analysis(FEA). In this paper, the maximum tangen-tial stress(MTS) criterion was used to predict crack growth direction. Not only experiment but also finite element analysis was carried out and the theoretical predictions were compared with experimental results.

평직 복합재료의 섬유 배열각도별 CFRP피로 균열 성장 평가

금진화(Jin-Hwa Geum),최정훈(Jung-Hun Choi),박홍선(Hong-Sun Park),구재민(Jae-Mean Koo),석창성(Chang-Sung Seok) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.6

많은 연구자들이 평직 탄소섬유강화플라스틱에 대해서 연구해왔지만 피로 균열 진전에 관한 연구는 아직도 미지한 상태이다. 그리고 하중과 섬유 배열 각도에 따라 균열 진전 양상이 다름을 알 수 있다. 본 연구에서는 서로 다른 두 개의 섬유 배열각도(0°, 45°)에서 평직 탄소섬유강화플라스틱의 피로 균열 진전에 대해 연구하였다. 평직 탄소섬유강화플라스틱의 피로 균열 진전 테스를 하중비 0.1에 10㎐로 수행하였다. 그 시험 결과로써, 피로 균열 진전 속도(da/dN)와 에너지해방률(ΔG)과의 그래프를 도출하였고, 섬유 배열 각도에 따른 균열 진전 양상을 0°의 경우에는 Mode I를 적용하였고, 45°의 경우에는 Mixed Mode를 적용하였다. Many researchers have studied woven fabric carbon-fiber-reinforced composite (CFRP) materials but the study of fatigue crack propagation in composites has been insufficient. It has known that the crack propagation behavior differs depending on the load and the fiber direction. In this study, the fatigue crack propagation along two different fiber array directions (0°, 45°) in plain woven CFRP composite was investigated. Fatigue crack propagation tests were conducted on the woven CFRP composite under a sinusoidal waveform load with stress ratios of 0.1 at a frequency of 10 ㎐. Once the results of the tests were obtained, fatigue crack propagation rates (da/dN) were plotted against the energy release rate amplitude (ΔG), and it was observed that either mode I crack propagation or mixed mode crack propagation occurs depending on the fiber array direction.

경사진 균열을 가진 직사각형 시편의 균열진전 거동 연구

우경식 ( Kyeong Sik Woo ),김영아 ( Young Ah Kim ),왕위 ( Wei Wang ) 충북대학교 건설기술연구소 2012 建設技術論文集 Vol.31 No.1

본 논문에서는 경사진 균열을 가진 사각형 인장시험 시편형상에 대해 반복계산에 의한 가상균열진전법과 CZM (Cohesive Zone Modeling) 방법을 사용하여 균열전파거동을 연구하였다. 사각형 시편형상은 2차원 평면요소를 사용* 하여 이산화 하였으며 경사진 균열을 외연적으로 나타내도록 모델링 하였다. 가상균열진전해석에서는 반복적으로 선형탄성파괴역학적 방법으로 균열전파 방향을 계산한 후 작은 크기의 斗상균열 크기만큼 균열크기를 증가시키도록 하였고, CZM 방법에서는 균열이 전파될 것으로 예측되는 지역에 위치한 모든 요소들 사이에 코히시브 요소를 삽입한 후 해석을 수행하여 해석형상의 응력상태에 따라서 균열의 전파경로가 결정되도록 하였다. 코히시브 트랙션-분리 관계식의 초기강성 및 요소의 형상 둥이 균열전파가 거동 에 미치는 영향을 체계적으로 조사하였다. In this paper, the crack propagation behavior of rectangular tensile specimen with slanted center crack was studied by an iterative virtual crack propagation method (IVCP) and cohesive zone modeling (CZM), The rectangular specimen configuration was discretized using 2-dimensional plane elements with the slanted center crack modeled explicitly. In the IVCP method, first the crack propagation direction was calculated by LEFM based methods and then a small sized virtual crack was extended successively. In the CZM method, the cohesive elements were inserted between the sides of every bulk element in the region where the crack was thought to propagate. The effect of the initial stiffness of the traction-separation relation and element shapes on the crack propagation behavior was systematically investigated.

Direct shear testing of brittle material samples with non-persistent cracks

Haeri, Hadi,Sarfarazi, Vahab,Shemirani, Alireza Bagher,Zhu, Zheming Techno-Press 2018 Geomechanics & engineering Vol.15 No.4

The mechanical behavior of the brittle material samples containing the internal and edge cracks are studied under direct shear tests. It is tried to investigate the effects of stress interactions and stress intensity factors at the tips of the pre-existing cracks on the failure mechanism of the bridge areas within these cracks. The direct shear tests are carried out on more than 30 various modeled samples each containing the internal cracks (S models) and edge cracks (E models). The visual inspection and a low power microscope are used to monitor the failure mechanisms of the tested samples. The cracks initiation, propagation and coalescences are being visualized in each test and the detected failure surfaces are used to study and measure the characteristics of each surface. These investigations show that as the ratio of the crack area to the total shear surface increases the shear failure mode changes to that of the tensile. When the bridge areas are fixed, the bridge areas in between the edge cracks have less strength than those of internal cracks. However, the results of this study show that for the case of internal cracks as the bridge area is increased, the strength of the material within the bridge area is decreased. It has been shown that the failure mechanism and fracture pattern of the samples depend on the bridge areas because as the bridge area decreases the interactions between the crack tip stress fields increases.

A molecular dynamics study on the biased propagation of intergranular fracture found in copper STGB

정하영,조맹효 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.11

Structural failure of the polycrystalline material is influenced by the interaction between the crystal and their boundaries. Specifically, a ductile material such as copper exhibit the different mechanisms of failure depending on the direction of the crack propagation within the grain boundary. Such directional anisotropy is often studied based on Rice’s criteria, which has the analytic solution in the grain boundary with [110] rotation of the axis. In this work, we expand the study of such intergranular directionality to a propagation within [100] grain boundary. This work introduces the inherent bias found in the intergranular fracture of [100] grain boundaries, using molecular dynamics simulations. Later, such observation is shown to agree with the relative crack propagation velocities, and cohesive energies obtained at the crack tip vicinity. These anisotropic trends are lastly correlated with the detailed atomistic movements observed during structural failures. These findings are to be used in improving the simulation capability and predictability of crack propagation.

Effect of Annealing and Crack Orientation on Fatigue Crack Propagation of Ti64 Alloy Fabricated by Direct Energy Deposition (DED) Process

Soyoung Kim,Hojun Oh,Jung Gi Kim,Sangshik Kim 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.1

Efects of annealing condition and crack orientation on fatigue crack propagation (FCP) behavior of DED (direct energydeposition)-processed Ti–6Al–4V (Ti64) specimens were studied. It was found that the FCP resistance of Ti64 increasedsignifcantly with annealing, particularly above β transus temperature, due to the microstructural coarsening inducing lessdamage accumulation at the tip of crack. The FCP behavior of as-built and as-annealed DED Ti64 specimens was isotropicwith crack direction either parallel or perpendicular to building direction. The detailed micrographic and fractographicanalyses on FCP-tested specimens suggested that the presence of largely elongated β grain boundaries did not afect theadvance of crack.

압연 및 용접방향이 같은 맞대기 용접강판의 하중방향에 따른 피로균열 진전특성

이용복,김성엽,오병덕,Lee Yong-Bok,Kim Sung-Yeup,Oh Byung-Duck 대한용접접합학회 2005 대한용접·접합학회지 Vol.23 No.6

Most of the welding steel plate structures have complicated mechanical problems such as rolling directional characteristics and residual stresses caused by manufacturing process. For the enhancement of reliability and safety in those structures, therefore, a systematic investigation is required. SS400 steel plate used for common structures was selected and welded by FCAW butt-welding process for this study, and then it was studied experimently about characteristics of fatigue crack propagations with respect to rolling direction and welding residual stress of welded steel plates. When the angles between rolling direction and tensile loading direction in base material are increased, their ultimate strength not show a significant difference, but yielding strength are increased and elongations are decreased uniformly. It is also shown that fatigue crack growth rate can be increased from those results. When the angles between welding bead direction and loading direction in welded material are increase, fatigue crack growth rate of them are decreased and influenced uniformly according to the conditions of residual stress distribution. In these results, it is shown that the welded steel plate structures are needed to harmonize distributed welding residual stress, rolling direction and loading direction fur the improvement of safety and endurance in manufacture of their structures.