• Title, Summary, Keyword: Brittle Failure

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Failure Criterion Including Brittle Damage (취성재의 결함을 고려한 파괴기준에 대한 연구)

  • Yoh, Eun-Gu;Lee, Yong-Shin
    • Proceedings of the KSME Conference
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    • pp.507-510
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    • 2001
  • Brittle failure mechanism has been well known as growth of initial micro-damage, that causes macro crack and failure in the end. Several precise criteria are suggested recently, based on experiments values in a whole load range. Among them, Mohr-Coulomb's criterion is used widely these days, but it has a big error compared with the real failure behavior since it does not show reciprocal actions of stresses. In this study, a new brittle failure criterion is proposed, which includes the effects of brittle damage evolution by taking a brittle damage parameter specifically. Comparisons between the proposed model and the previous ones are also given.

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Damage-controlled test to determine the input parameters for CWFS model and its application to simulation of brittle failure (CWFS모델변수 결정을 위한 손상제어시험 및 이를 활용한 취성파괴모델링)

  • Cheon, Dae-Sung;Park, Chan;Jeon, Seok-Won;Jung, Yong-Bok
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.9 no.3
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    • pp.263-273
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    • 2007
  • When a tunnel or an underground structure is excavated in deep geological environments, the failure process is affected and eventually dominated by stress-induced fractures growing preferentially parallel to the excavation boundary. This fracturing is generally referred to as brittle failure by spatting and slabbing. Continuum models with traditional failure criteria such as Hoek-Brown or Mohr-Coulomb criteria have not been successful in prediction of the extent and depth of brittle failure. Instead cohesion weakening and frictional strengthening (CWFS) model is known to predict brittle failure well. In this study, CWFS model was applied to predict the brittle failure around a circular opening observed in physical model experiments. To obtain the input parameters for CWFS model, damage-controlled tests were carried out. The predicted depth and extent of brittle failure using CWFS model were compared to the results of the physical model experiment and numerical simulation using traditional model.

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The extent and depth of brittle failure around circular tunnel with stress conditions (응력조건에 따른 원형터널 주변의 취성파괴범위와 파괴심도)

  • Cheon, Dae-Sung;Park, Chul-Whan;Jeon, Seok-Won;Park, Chan
    • Tunnel and Underground Space
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    • v.17 no.4
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    • pp.311-321
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    • 2007
  • Failure of underground structures in hard rocks is a function of the in-situ stress, the intact rock strength and the distribution of fractures in the rock mass. At highly stressed regime, brittle failure is often observed due to excavation-induced stress. The characteristics of brittle failure are classified as failure grade, failure initiation stress, extent of failure and depth of failure. For safety construction of underground structures, these characteristics of brittle failure with stress conditions should be understood. In this study we evaluated the relationship between the extent and depth of failure with stress conditions for failure happened model specimens through true triaxial model experiments. The extent and depth of failure were determined using visual observation and computed tomography (CT). The results indicate that the depth of failure was affected by differential stress perpendicular to the axis of tunnel. However the extent of failure was irrelevant to the stress conditions.

Numerical modeling of brittle failure of the overstressed rock mass around deep tunnel (심부 터널 주변 과응력 암반의 취성파괴 수치모델링)

  • Lee, Kun-Chai;Moon, Hyun-Koo
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.18 no.5
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    • pp.469-485
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    • 2016
  • The failure of rock mass around deep tunnel, different from shallow tunnel largely affected by discontinuities, is dominated by magnitudes and directions of stresses, and the failures dominated by stresses can be divided into ductile and brittle features according to the conditions of stresses and the characteristics of rock mass. It is important to know the range and the depth of the V-shaped notch type failure resulted from the brittle failure, such as spalling, slabbing and rock burst, because they are the main factors for the design of excavation and support of deep tunnels. The main features of brittle failure are that it consists of cohesion loss and friction mobilization according to the stress condition, and is progressive. In this paper, a three-dimensional numerical model has been developed in order to simulate the brittle behavior of rock mass around deep tunnel by introducing the bi-linear failure envelope cut off, elastic-elastoplastic coupling and gradual spread of elastoplastic regions. By performing a series of numerical analyses, it is shown that the depths of failure estimated by this model coincide with an empirical relation from a case study.

Study of Brittle Failure (취성파괴에 관한 고찰)

  • Cheon, Dae-Sung;Synn, Joong-Ho;Jeon, Seo-Kwon;Park, Chan
    • Tunnel and Underground Space
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    • v.16 no.6
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    • pp.437-450
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    • 2006
  • Failure around an underground opening is a function of in-situ stress magnitudes, intact rock strength and the distribution of fractures in the rock mass. At high in-situ stress, the failure process is affected and eventually dominated by stress-induced fractures preferentially growing parallel to the excavation boundary. This fracturing is often observed in brittle type of failure such as slabbing or spatting. Recent studies dies on the stress-induced damage of rock revealed its importance especially in a highly stressed regime. As the constructions of underground structures at deep depths increased, the cases of the brittle failure also increased and furthermore spalling was occurred in Korea at low depths. To improve the stability of the underground structures at highly stressed regime, the characteristics of brittle failure should be examined, but they have not yet been properly investigated. Therefore in this report the characteristics of brittle failure such as types, failure mechanism and modeling methods etc. were considered in all aspects, based on the previous researches.

Crack Analysis of the Quasi-Brittle Materials Using a Stochastic Model (물성의 확륙적 분포를 이용한 Quasi-Brittle 재료의 균열해석)

  • 임윤목;김문겸;신승교;박진완
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.217-222
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    • 1999
  • Usually, the failure of quasi-brittle materials is numerically difficult to describe because of the localization process with softening behavior. In this study, ADLE(Axial Deformation Link Elements) with stochastic material properties are developed to simulate the quasi-brittle material failure behavior. The ADLE method is adopted both Fictitious Crack Model and stochastic method to implement the fracture behavior with the localization behavior of quasi-brittle materials. The main objective of this paper is to show the mash independency and the capability of ADLE for the failure behavior of a quasi-brittle materials.

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Characteristics of the Progressive Brittle Failure around Circular Opening by Scaled Model Test and Discrete Element Analysis (축소 모형시험과 개별 요소 해석에 의한 원형 공동 주변의 점진적 취성파괴 특성에 관한 연구)

  • Jeon Seok-Won;Park Eui-Seob;Bae Seong-Ho
    • Tunnel and Underground Space
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    • v.15 no.4
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    • pp.250-263
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    • 2005
  • Progressive and localized brittle failures around an excavated opening by the overstressed condition can act as a serious obstacle to ensure the stability and the economical efficiency of construction work. In this paper, the characteristics of the brittle failure around an circular opening with stress level was studied by the biaxial compressive test using sealed specimen and by the numerical simulation with $PFC^{2D}$, one of the discrete element codes. The occurring pattern and shape of the brittle failure around a circular opening monitored during the biaxial loading were well coincided with those of the stress induced failures around the excavated openings observed in the brittle rock masses. The crack development stages with stress level were evaluated by the detailed analysis on the acoustic emission event properties. The microcrack development process around a circular opening was successfully visualized by the particle flow analysis. It indicated that the scaled test had a good feasibility in understanding the mechanism of the brittle failure around an opening with a high reliability.

Stability evaluation and microseismic monitoring around Large Underground Oil Storage Cavern in Over-stressed Rock Mass (과지압 암반 내 대규모 지하 유류비축기지 안정성 평가 및 Microseismic 계측)

  • Lee Hee-Suk;Lee Dae-Hyuck;Kim Ho-Yeong;Hong Jee-Soo;Choi Young-Tae;Kim Seok-Jin;Park Yeon-Jun
    • 한국터널공학회:학술대회논문집
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    • pp.189-201
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    • 2005
  • Brittle failure has been detected in over-stressed rock mass during the construction of oil storage cavern. The main characteristics of stress induced brittle failure of the site are introduced. Various evaluation and measures are sought to stabilize the over-stressed rock mass. The major results from numerical analysis of the cavern are presented, and from current microseismic monitoring to detect hazard from brittle failure are presented.

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A Boundary Element Analysis for Damage and Failure Process of Brittle Rock using ERACOD (FRACOD를 이용한 취성 암석의 손상 및 파괴에 대한 경계요소 해석)

  • ;Baotang Shen;Ove Stephansson
    • Tunnel and Underground Space
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    • v.14 no.4
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    • pp.248-260
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    • 2004
  • Damage in brittle rock due to stress increase starts from initiation of microcracks, and then results in failure by forming macro failure planes due to propagation and coalescence of these discrete cracks. Conventionally, continuum approaches using macro-failure criteria or a number of elasto-plastic models have been major solution to implement rock damage and failure. However, actual brittle failure processes can be better described in phenomenological approach if initiation and propagation of discrete fractures are explicitly considered. This study presents damage and failure process of rock using a boundary element code, FRACOD, which has been developed to model fracturing process of rocks. Through a series of numerical uniaxial compressive tests, the feasibility of the developed model was verified, and realistic rock failure process was reproduced considering scale effects in rocks. In addition, the fracturing process and the corresponding rock damage in the vicinity of deep shaft in rock mass were presented as an application of this approach. This approach will be expected to contribute to finding better engineering solutions for the analysis of stability problems in brittle rock masses.

Fracture Analysis of Porous Titanium for Dental Implant Fabricated by Space Holder Process (Space holder 공정으로 제조된 치과 임플란트용 타이타늄 다공체의 파손 분석)

  • Lee, Seung-Mi;Jang, Jin-Man;Lee, Won-Sik;Byeon, Jai-Won
    • Journal of Applied Reliability
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    • v.16 no.2
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    • pp.104-109
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    • 2016
  • Purpose: The purpose of this study is to analyze fracture behavior and failure mechanism of porous titanium for dental implant fabricated by space holder process. Method: Three porous titanium specimens with a specific volume fraction of open pore were test by 3 point bending and compression stress condition, respectively. Fracture appearance was observed by scanning electron microscope and discussed in relation with oxygen content. Results: For compression-tested specimens, two specimen showed brittle failure, while the other one showed normal failure after deformation. High oxygen content was detected in the brittle-fractured specimen. Several micro-cracks initiated at the struts propagated down to the bottom of the specimen resulting in normal failure. Conclusion: Oxygen contamination during the fabrication process can leads brittle premature failure, and hence quality problem of the porous titanium for dental implant.