• 한국생산제조학회지
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• 제8권2호
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• pp.126-136
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• 1999

We studied on crack growth retardation in single overloading condition. Crack tip branching which as the second mechanism on crack growth retardation was examined. Crack tip branching was observed to kinked type and forked type. It was found that the branching angle range was from 25 to 53 degree. The variations of crack driving force with branching angle were calculated with finite element method The variation of {{{{ KAPPA _I}}}}, {{{{ KAPPA _II}}}} and total crack driving force(K) were examined respectively So {{{{ KAPPA _I}}}}, {{{{ KAPPA _II}}}} and K mean to mode I, II and total crack driving force. Present model(Willenborg's model) for crack growth retardation prediction was modified to take into consideration the effects of crack tip branching When we predicted retardation with modified model. it was confirmed that predicted and experimental results coincided with well each other.

• International Journal of Precision Engineering and Manufacturing
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• 제3권3호
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• pp.76-81
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• 2002

In order to study the fatigue crack and retardation mechanism in variable loading, the effects of crack tip branching in crack growth retardation were examined. The characteristics of crack tip branching behavior were considered with respect to microstructure and crack tip branching angle was examined. Crack tip branching was observed along the grain boundary of finite and pearlite structure. It was found that the branching angle ranges from 25 to 53 degrees. Using the finite element method, the variable of crack driving farce to branching angle was examined. The effective crack driving farce (K$\_$eff/) decreased as the branching angle increased. The rate of decrease was 33% for kinked type and 29% for forked one. It was confirmed that the effect of crack tip branching is a very important factor in crack growth retardation. Therefore, crack branching effect should be considered in building the hypothetical model to predict crack growth retardation.

• Journal of the Korean Data and Information Science Society
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• 제25권5호
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• pp.1137-1149
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• 2014

Since the bifurcating autoregressive (BAR) model was developed by Cowan and Staudte (1986) to analyze cell lineage data, a lot of research has been directed to BAR and its generalizations. Based mainly on the author's works, this paper is concerned with a contemporary review on the BAR in terms of an overview and perspectives. Specifically, bifurcating structure is extended to multi-cast tree and to branching tree structure. The AR(1) time series model of Cowan and Staudte (1986) is generalized to tree structured random processes. Branching correlations between individuals sharing the same parent are introduced and discussed. Various methods for estimating parameters and related asymptotics are also reviewed. Consequently, the paper aims to give a contemporary overview on the BAR model, providing some perspectives to the future works in this area.

• 한국정보과학회논문지:시스템및이론
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• 제27권2호
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• pp.123-134
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• 2000

등치선(wire-frame contour)으로 표현된 물체의 볼륨정보에서부터 3차원 표면을 재구성하는 방법을 제안한다. 등치선 삼각화법(contour triangulation)이라고도 하는 이 방법에서 가장 문제가 되는 것이 인접 단층사이에서 표면이 분기하는 경우에 발생하는데, 이것은 하나의 등치선이 인접한 층의 두 개이상의 등치선과 연결되는 형태로 나타나며, 표면 생성시의 많은 모호성을 발생시킨다. 본 논문에서는 이러한 분기문제를 가장 일반적으로 발생하는 이중분기문제와 그 이상의 다중분기문제로 구분하고, 먼저 이중 분기 알고리즘을 제안하였으며, 다중분기문제를 다수의 이중분기문제로 단순화하는 다중분기 알고리즘을 제안하였다. 제안된 이중분기 알고리즘은 모 등치선을 분할하는 방법을 이용하였는데, 먼저 해협다각형을 정의하고 이를 삼각분할하여 분할선을 구하는 것에 바탕을 두고 있다. 이 방법은 이중분기가 매우 복잡하게 나타나는 경우에도 잘 적용이 되며, 분할선의 레벨을 조절함으로써 매우 사실적인 표면을 만들어 낼 수 있다는 장점이 있다. 또한 다중분기문제를 단층 간격의 문제로 규정하고, 인접한 두 층 사이에 가상의 등치선을 추가하여 가지 등치선을 연속적으로 병합하는 방법으로 해결하였다. 제안된 방법은 등치선 삼각화의 가장 큰 문제인 분기문제를 해결하기 위한 매우 구조적인 접근방법으로, 다양한 실제 등치선 데이타에 적용한 결과 좋은 성능을 나타냈다.

• 한국정밀공학회지
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• 제14권6호
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• pp.83-89
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• 1997

In order to study on fatigue crack retardation and retardation mechanism in variable loading, the effects of crack tip branching in fatigue crack growth retardation were examined. The characteristics of crack tip banching behavior was considered to micro structure. It was examined that the variation of crack tip branching angle. Crack tip branching was observed along the grain boundary of ferrite and pearlite structure. It was found that the abanching angle ranges from 25 to 53 degrees. Using the finite element method, the variable of crack driving force to branching angle was examined. The effective crack driving force ( $K_{\eff}$ ) decreased as the braching angle increases. The rate of decrease was 33% for the kinked type and 29% for the forked one. It was confirmed that the effect of crack tip branching is a very important factor in fatigue crack growth retardation. Therefore, crack branching effect should be considered building the hypoth- etical model to predict crack growth retardation.

• Structural Engineering and Mechanics
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• 제75권3호
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• pp.339-356
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• 2020

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.

• 한국전산구조공학회논문집
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• 제24권6호
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• pp.637-643
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• 2011

본 논문에서는 결합 기반 페리다이나믹스 해석법을 사용하여 동적취성 파괴시뮬레이션을 수행하였다. 페리다이나믹스 모델은 분기 균열, 균열 불안정성, 균열 경로의 비대칭성, 연쇄 분기 균열, 2차 균열 전파 등 다양한 동적취성 파괴현상을 잘 해석해 낼 수 있다. 본 논문에서는 분기 균열의 분기 각도와 균열 전파속도에 대한 응력파의 영향에 대해 연구하였다. 극한 시점에 도달한 균열은 둘 이상으로 분기되어 전파되고 그 전파속도는 기존 균열의 전파속도와 크게 달라지지 않는다는 사실이 여러 실험을 통해서 입증이 되었다. 페리다이나믹스로 해석된 분기 균열은 실험을 통해 제안된 균열 전파현상들과 잘 부합되는 것을 확인할 수 있었다.

• 한국전산구조공학회논문집
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• 제28권3호
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• pp.309-316
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• 2015

상태 기반 페리다이나믹 모델은 일반적인 재료 구성 모델을 구현할 수 있고 비국부 영역 내에서 연결된 모든 결합의 변형을 통해 각 절점의 재료 응답이 결정되기 때문에 체적 및 전단 변형을 모두 표현할 수 있다. 따라서 상태 기반 모델은 복잡한 동적 취성 파괴 현상(분기균열, 2차 균열, 계단균열, 균열 유착 등)을 해석하는데 유용하다. 본 논문에서는 평면응력 탄성체에 대해 2차원 상태 기반 페리다이나믹 모델을 적용하고 에너지해방율과 페리다이나믹 에너지 포텐셜로부터 손상 모델을 구성하였다. 페리다이나믹 파괴 해석 모델을 통해 취성 유리 재료에 대해 균열 면에 평행한 압축 응력파가 균열 분기 패턴에 미치는 영향에 대해 조사하였다. 실험을 통해 관찰된 동적 균열 진전 및 분기 패턴에 대한 주요 특성들이 페리다이나믹 해석을 통해 확인되었다. 또한 강한 인장 하중 하의 계단균열과 이차균열 등이 상태 기반 페리다이나믹 시뮬레이션을 통해 잘 모사가 되는 것을 확인할 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.765-768
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• 2003

The objective of the present study was to visualize the pulsatile flow field in a branching model by using the high-resolution PIV system. A bifurcated flow system was built for the experiments in the pulsatile flow. Harvard pulsatile pump was used to generate the pulsatile velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow fields. Two consecutive particle images at several cross sections of the flow filed were captured by the CCD cameras ($1K{\ast}1K$ and $640{\ast}480$). The results after the image processing clearly showed the recirculation zones and the formation of the paired secondary flows from the distal to the apex in the bifurcated model. The results also indicated that the flow velocities in the inner wall moved faster than those in the outer wall due to the inertial force effects and the helical motions generated in the branch flows as the flow proceeded toward the outer wall. While the PIV images from the $1K{\ast}1K$ camera were closer to the simulation results thantheimagesfromthe640${\ast}$480camera,bothresultsofthePIVexperimentsusingthetwocamerasgenerallyagreed quitewellwiththeresultsfromthenumericalsimulation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.830-833
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• 2005

SDM(Structural Dynamics Modification) is to improve dynamic characteristics of a structure, more specifically of a base structure, by adding or deleting auxiliary(modifying) structures. In this paper, I will focus on the optimal layout of the stiffeners which are attached to the plate to maximize 1st natural frequency. Recently, a new topology method was proposed by yamazaki. He uses growing and branching tree model. I modified the growing and branching tree model. The method is designated modified tree model. To expand the layout of stiffeners, I will consider non-matching problem. The problem is solved by using local lagrange multiplier without the mesh regeneration. Moreover The CMS(Component mode synthesis) method is employed to reduce the computing time of eigen reanalysis using reduced componet models.