• Title, Summary, Keyword: 균열전파 이론

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Peridynamic models for dynamic fracture in brittle materials (취성 재료의 동적 파괴 해석을 위한 Peridynamics 모델)

  • Ha, Youn-Doh
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.561-564
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    • 2011
  • 다양한 공학/산업적 측면에서 동적 취성 파괴 현상은 매우 중요하다. 취성 균열은 다른 균열 전파에 비해 그 전파 속도가 매우 빠르고 전파 범위가 넓기 때문에 대규모의 파괴 현상을 일으킨다. 동적 전파 중인 취성 균열 거동을 모델화하기 위해 오랜 기간 동안 많은 연구가 진행되었지만, 여전히 많은 부분들이 해석되지 못한 채 남아있다. 특히 균열 생성 및 전파를 위해 인위적인 조건들을 도입해야 하는 것은 기존 방법론들이 가지는 공통적인 문제점이다. 본 연구는 peridynamics를 동적 분기 균열 문제 해석에 도입한다. Peridynamics는 전통적인 연속체 이론에 기반한 수치해석 모델화 기법으로 균열과 같은 비연속성이 있는 문제의 모델화에 강점이 있으며, 인위적인 조건 없이 매우 간단한 방법으로 파괴 현상을 해석할 수 있다. 본 연구에서는 peridynamics 모델이 실험적으로 관측된 분기균열 형상과 균열 전파 속도를 매우 잘 예측해 낼 수 있음을 보인다. 또한 균열팁 주변에 높은 응력이 발생할 때 나타나는 연쇄 분기 현상도 해석할 수 있다. 이와 같은 연구를 통해 응력파가 균열 전파 속도를 변화시키고 전파 방향에도 영향을 주는 것을 알 수 있었다. 수치해석 결과도 또한 실험 결과들과 잘 부합함을 확인하였다.

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부식피로

  • 권영각
    • Journal of the KSME
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    • v.29 no.2
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    • pp.138-143
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    • 1989
  • 부식피로에 대한 몇 가지 이론 및 실제를 소개하였다. 그러나, 부식피로가 학문적으로 관심을 갖게되고 연구의 대상이 된 것은 1970년초 부터로서, 아직까지도 많은 부분이 연구대상으로 남 아있다. 특히, 균열선단에서의 부식반응의 역할이 좀 더 상세히 밝혀져야 하고, 자연 부식조건 에서의 양극반응과 음극반응이 각각 어떠한 역할을 하는가도 좀더 밝혀져야 할 것이다. Mode II 또는 Mode III 상태에서의 균열전파 특성이나, 균열전파에 있어서 반복응력의 주파수의 영 향도 좀더 상세히 밝혀져야 할 연구 대상이다. 이러한 연구들을 통해서 현재까지는 주로 부식의 측면에서만 고려되는 산업현장의 부식피로 문제에 대해 좀더 근본적이고 효과적인 해결 방법을 제시할 수 있을 것이다.

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Modeling of Multi-Stage Hydraulic Fracture Propagation (다단계 수압파쇄균열 전파 모델링 연구)

  • Jang, Youngho;Sung, Wonmo
    • Journal of the Korean Institute of Gas
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    • v.19 no.5
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    • pp.13-19
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    • 2015
  • This paper presents a hydraulic fracture propagation model to describe propagation more realistically. In propagating the hydraulic fractures, we have used two criteria: maximum tangential stress to determine the fracture initiation angle and whether a hydraulic fracture intersects a natural fracture. The model was validated for the parameters relevant to fracture propagation, such as initiation angle and crossing ability through natural fracture. In order to check whether a hydraulic fracture crosses a natural fracture, the model results on crossing state excellently matched with the experimental data. In the sensitivity analysis for direction of maximum horizontal stress, frictional coefficient of fracture interface, and natural fracture orientation, the results show that hydraulic fracture intersects natural fracture, and then, propagated suitably with theoretical results according to fracture interaction criterion. In comparison of this model against vertical fracture approach, it was ascertained that there are discrepancies in fracture connectivity and stimulated reservoir volume.

Peridynamic Modeling for Crack Propagation Analysis of Materials (페리다이나믹 이론 모델을 이용한 재료의 균열 진전 해석)

  • Chung, Won-Jun;Oterkus, Erkan;Lee, Jae-Myung
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.31 no.2
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    • pp.105-114
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    • 2018
  • In this paper, the computer simulations are carried out by using the peridynamic theory model with various conditions including quasi-static loads, dynamic loads and crack propagation, branching crack pattern and isotropic materials, orthotropic materials. Three examples, a plate with a hole under quasi-static loading, a plate with a pre-existing crack under dynamic loading and a lamina with a pre-existing crack under quasi-static loading are analyzed by computational simulations. In order to simulate the quasi-static load, an adaptive dynamic relaxation technique is used. In the orthotropic material analysis, a homogenization method is used considering the strain energy density ratio between the classical continuum mechanics and the peridynamic. As a result, crack propagation and branching cracks are observed successfully and the direction and initiation of the crack are also captured within the peridynamic modeling. In case of applying peridynamic used homogenization method to a relatively complicated orthotropic material, it is also verified by comparing with experimental results.

Crack Coalescence in Rock Bridges under Uniaxial Compression (단축압축 하의 암석 브릿지에서의 균열 결합)

  • Park, Nam-Su;Jeon, Seokwon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.3 no.2
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    • pp.23-32
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    • 2001
  • Rock masses are usually discontinuous in nature, as a result of various geological processes they have underdone and they contain rock joints and bridges. Crack propagation and coalescence processes mainly cause rock failures in tunnels. In this study, we focused on the crack initiation, propagation and coalescence process of rock materials containing two pre-existing open cracks arranged in different geometries. During uniaxial compression, wing crack initiation stress, wing crack propagation angle, and crack coalescence stress of Diastone gypsum and Yeosan Marble specimens were examined. And crack initiation, propagation, and coalescence processes were observed. Shear, tensile and mixed (shear+tensile) types of crack coalescence occurred. To compare the experimental results with Ashby & Hallam model, crack coalescence stress was normalized and it generally agreed with the experimental results.

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A Study on the Interfacial Crack Propagation Criterion for Two Dissimilar Isotropic Bimaterial by the Static Photoelastic Experimental Hybrid Method (정적 광탄성 실험 하이브리드 법에 의한 두 상이한 등방성 이종재료의 계면균열전파 기준에 관한 연구)

  • Tche, Konstantin;Hawong, Jai-Sug;Shin, Dong-Chul;Nam, Sung-Su;Nam, Jeong-Hwan
    • Proceedings of the KSME Conference
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    • pp.1216-1221
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    • 2003
  • The specimen materials used in this research is bimaterial. The static photoelastic experiment was applied to them. And then the specimens used in photoelastic experiment were fractured under static load. The static photoelastic hybrid method was introduced and it's validity had been assured. The static photoelastic hybrid method was applied to the Minimum Strain Energy Density Criterion, the Maximum Tangential Stress Criterion and Mode Mixity. Crack propagation criterion by the static photoelastic hybrid method was introduced and it was applied to the above various failure theories. Comparing the experimental initial angle of crack propagation with the theoretical initial angle of crack propagation from the various failure criterions. And then the optimal crack propagation criterion was suggested and it's validity was assured.

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Application of the Static Photoelastic Experimental Hybrid Method to the Crack Propagation Criterion for Isotropic Materials (등방성체의 균열전파 기준에 정적 광탄성 실험 하이브리드 법 적용)

  • Shin Dong-Chul;Hawong Jai-Sug;Nam Sung-Su
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.8
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    • pp.1229-1236
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    • 2004
  • The specimen materials used in this research are isotropic epoxy resins. The static photoelastic experiment was applied to them. And then the specimens used in photoelastic experiment were fractured under static load. The static photoelastic experimental hybrid method was introduced and its validity had been assured. Crack propagation criterion used the stress components, which are considered the higher order terms, obtained from the static photoelastic experimental hybrid method was introduced and it was applied to the minimum strain energy density criterion, the maximum tangential stress criterion and mode mixity. Comparing the actual initial angle of crack propagation with the theoretical initial angle of crack propagation obtained from the above failure criterions, the validities of the above two criterions are assured and the optimal distance (r) from the crack-tip is 0.01mm in order to get the initial angle of crack propagation of isotropic epoxy resin.

A Study on the Crack Propagation Criterion of Orthotropic Material by the Static Photoelastic Experimental Hybrid Method (정적 광탄성 실험 하이브리드법에 의한 직교이방성체의 균열전파 기준에 관한 연구)

  • Shin, Dong-Chul;Hawong, Jai-Sug;Nam, Sung-Su;Kwon, O-Sung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.11
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    • pp.1799-1806
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    • 2004
  • The static photoelastic experiment was applied to orthotropic materials. And then the specimens used in photoelastic experiment were fractured under static load. The static photoelastic experimental hybrid method for orthotropic material was introduced and its validity had been assured. Crack propagation criterion used the stress components, which are considered the higher order terms, obtained from the static photoelastic experimental hybrid method was introduced and it was applied to the minimum strain energy density criterion, the maximum tangential stress criterion and mode mixity. Comparing the actual initial angle of crack propagation with the theoretical initial angle of crack propagation obtained from the above failure criterions, the validities of the above two criterions are assured and the optimal distance (${\gamma}$) from the crack-tip is 0.01mm in order to get the initial angle of crack propagation of orthotropic material(C.F.E.C.).

Crack Propagation and Coalescence in Yeosan Marble under Uniaxial Compression (단축압축 하에서 대리석의 균열전파 및 결합)

  • 박남수;전석원
    • Tunnel and Underground Space
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    • v.11 no.3
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    • pp.217-224
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    • 2001
  • Rock masses are usually discontinuous in nature due to various geological processes and contain rock joints and bridges. Crack propagation and coalescence processes in rock bridge mainly cause rock failures in slopes, foundations, and tunnels. In this study, we focused on the crack initiation, propagation and coalescence process of rock materials containing two pre-existing open cracks arranged in different geometries. Specimens of 120${\times}$60${\times}$25 mm in size, which were made of Yeoman Marble, were prepared. In the specimens, two artificial cracks were cut with pre-existing crack angle ${\alpha}$, bridge angle ${\beta}$, pre-existing crack length 2c and bridge length 2b. Wing crack initiation stress, wing crack propagation angle, and crack coalescence stress were measured and crack initiation, propagation and coalescence processes were observed during uniaxial compression. Crack coalescence types were classified and analytical study using Ashby and Hallam model (1986) was performed to be compared with the experimental results.

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Propagation Behavior of Inclined Surface Crack of Semi-Infinite Elastic Body under Hertzian Contact (반무한 탄성체의 헤르츠 접촉하의 경사진 표면균열의 전파거동)

  • 김재호;김석삼;박중한
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.3
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    • pp.624-635
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    • 1990
  • Analytical study based on linear fracture mechanics was conducted on propagation behavior of inclined surface crack in semi-infinite elastic body. The analytical model was assumed to be inclined surface crack under plane strain condition upon which Hertzian stress was superimposed. Supposing continuous distribution of dislocation and applying Erdogan-Gupta's method to this crack problem, the stress intensity factors $K_{I}$ and $K_{II}$) at the crack-tip were obtained for various Hertzian contact positions. Analytic results have shown that driving force for crack growth is $K_{I}$ for non-lubricated condition and $K_{II}$ for fluid and boundary lubricated condition. The coefficient of friction at the hertzian contact and crack surfaces plays an important role in predicting the direction of crack propagation. It is also found that the maximum effective stress intensity factor exists at cracks of a certain specific length depending on lubricated condition.ion.n.