• Title/Summary/Keyword: Stress discontinuity

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A local-global scheme for tracking crack path in three-dimensional solids

  • Manzoli, O.L.;Claro, G.K.S.;Rodrigues, E.A.;Lopes, J.A. Jr.
    • Computers and Concrete
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    • v.12 no.3
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    • pp.261-283
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    • 2013
  • This paper aims to contribute to the three-dimensional generalization of numerical prediction of crack propagation through the formulation of finite elements with embedded discontinuities. The analysis of crack propagation in two-dimensional problems yields lines of discontinuity that can be tracked in a relatively simple way through the sequential construction of straight line segments oriented according to the direction of failure within each finite element in the solid. In three-dimensional analysis, the construction of the discontinuity path is more complex because it requires the creation of plane surfaces within each element, which must be continuous between the elements. In the method proposed by Chaves (2003) the crack is determined by solving a problem analogous to the heat conduction problem, established from local failure orientations, based on the stress state of the mechanical problem. To minimize the computational effort, in this paper a new strategy is proposed whereby the analysis for tracking the discontinuity path is restricted to the domain formed by some elements near the crack surface that develops along the loading process. The proposed methodology is validated by performing three-dimensional analyses of basic problems of experimental fractures and comparing their results with those reported in the literature.

An Improved Mesh-free Crack Analysis Technique Using a Singular Basis Function (특이기저함수를 이용하여 개선한 Mesh-free 균열해석기법)

  • 이상호;윤영철
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.14 no.3
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    • pp.381-390
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    • 2001
  • In this paper, a new improved crack analysis technique by Element-Free Galerkin(EFG) method is proposed, in which the singularity and the discontinuity of the crack successfully described by adding enrichment terms containing a singular basis function to the standard EFG approximation and a discontinuity function implemented in constructing the shape function across the crack surface. The standard EFG method requires considerable addition of nodes or modification of the model. In addition, the proposed method significantly decreases the size of system of equation compared to the previous enriched EFG method by using localized enrichment region near the crack tip. Numerical example show the improvement and th effectiveness of the previous method.

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A Study on Joint by Two-Stage Excavation in Tunnel (2단계로 굴착되는 터널의 절리에 대한 연구)

  • Byun Gwang-Wook;An Joung-Hwan;Kim Dong-Gab;Lee Sang-Duk
    • Tunnel and Underground Space
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    • v.15 no.3 s.56
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    • pp.185-194
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    • 2005
  • Recently, the surrounding rock mass is understood as the major support system for the tunnel constructed in the rock mass. Generally, the rock mass contains many discontinuity planes such as joints, and thus, the tunnel behavior in the rock mass is governed by the characteristics of the discontinuity planes. In this study, the behavior of tunnel in jointed rock mass is studied by model tests and numerical analyses. The results shows that the behavior of tunnel depends on the different initial stress conditions, in case that the tunnel is excavated in the ground without any joints. When a joint is located near the tunnel, the pound stress and displacement tend to increase between the tunnel and the joint.

Numerical Approach for Determination of Shut-in Pressure in Hydrofracturing Test (수압파쇄 균열폐쇄압력 산정을 위한 수치해석 연구)

  • Choi, Sung-O.
    • Tunnel and Underground Space
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    • v.21 no.2
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    • pp.128-137
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    • 2011
  • The shut-in pressure calculated in common hydrofracturing test for vertical borehole equals generally to the minimum horizontal principal stress, so it should be considered as an essential parameter for determining the in-situ stress regime around the rock mass. It shows usually an ambiguous value in pressure-time history curves, however, because of the relationship between the behavior of hydraulic fractures and the condition of remote stress regime. In this study, a series of numerical analyses have been carried out to compare several methods for determining the shut-in pressure during hydrofracturing. The hydraulic-mechanical coupling has been applied to numerical analysis for simulating the fracture propagation by hydraulic pressure, and the different discontinuity geometry has been considered in numerical models to examine the effect of numerical element shape on fracture propagation pattern. From the numerical simulations with the four different discontinuity geometries, it was revealed that the shut-in pressure obtained from graphical methods rather than statistical method was relatively small. Consequently a care should be taken in selecting a method for determining the shut-in pressure when a stress anomaly around borehole and a fracture propagation with complicate mechanism are considered.

Investigating the Stress on Fault Plane Associated with Fault Slip Using Boundary Element Method (경계요소법을 이용한 단층 슬립에 따른 단층면 응력에 관한 연구)

  • Sung Kwon, Ahn;Hee Up, Lee;Jeongjun, Park;Mintaek, Yoo
    • Tunnel and Underground Space
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    • v.32 no.6
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    • pp.598-610
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    • 2022
  • Avoiding a fault zone would be a best practice for safety in underground construction, which is only sometimes possible because of many restrictions and other field conditions. For instance, there is an ongoing conception of Korea-Japan subsea tunnels that inevitably cross a massive fault system in the Korea Strait. Therefore it was deemed necessary to find an efficient way of predicting the likely behaviour of underground structures under fault slip. This paper presents the findings from simple numerical analysis for investigating the stress induced at a normal fault with a dip of 45 degrees. We used a boundary element software that assumed constant displacement discontinuity, which allowed the displacement to be estimated separately at both the fault's hangingwall and footwall sides. The results suggested that a principal stress rotation of 45 degrees occurred at the edges of the fault during the slip, which was in agreement with the phenomenon for fault plane suggested in the body of literature. A simple numerical procedure presented in this paper could be adopted to investigate other fault-related issues associated with underground structure construction.

Analysis of stress distribution around tunnels by hybridized FSM and DDM considering the influences of joints parameters

  • Nikadat, Nooraddin;Marji, Mohammad Fatehi
    • Geomechanics and Engineering
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    • v.11 no.2
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    • pp.269-288
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    • 2016
  • The jointed rock mass behavior often plays a major role in the design of underground excavation, and their failures during excavation and in operation, are usually closely related to joints. This research attempts to evaluate the effects of two basic geometric factors influencing tunnel behavior in a jointed rock mass; joints spacing and joints orientation. A hybridized indirect boundary element code known as TFSDDM (Two-dimensional Fictitious Stress Displacement Discontinuity Method) is used to study the stress distribution around the tunnels excavated in jointed rock masses. This numerical analysis revealed that both the dip angle and spacing of joints have important influences on stress distribution on tunnel walls. For example the tensile and compressive tangential stresses at the boundary of the circular tunnel increase by reduction in the joint spacing, and by increase the dip joint angle the tensile stress in the tunnel roof decreases.

Optimal Thickness Design of Ellipsoidal and Tori-Spherical Pressure Vessel Domes (타원형 및 토리-구형 압력용기도옴의 두께 최적화설계)

  • 이영신;김영완;조원만
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.3
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    • pp.707-715
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    • 1994
  • This study presents thickness optimization for the pressure vessel domes subject to internal pressure and axial force simultaneously. The considered typical pressure vessel domes are ellipsoidal and tori-spherical domes with skirt and nozzle part. These pressure vessel domes under loading have higher stress concentration on geometric discontinuity parts. Therefore, thickness optimization of axi-symmetric pressure vessel domes is essentially concerned on minimizing this stress concentration. The objective function is minimization of weight of pressure vessel dome. The design variable is thickness of dome and cylinder. Considered constraint is Von Mises equivalent stress. In the optimization procedure, ANSYS code is used. The equivalent and hoop stress of original shape domes are compared with those of optimal shape domes. And optimal thicknesses for pressure vessel domes are presented.

Rock Stress Measurement and Numerical Approach for Cavern Designing

  • Sugawara, Katsuhiko;Sakaguchi, Kiyotoshi;Obara, Yuzo;Nakayama, Tomoharu;Jang, Hyun-Kuk
    • Tunnel and Underground Space
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    • v.2 no.1
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    • pp.164-176
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    • 1992
  • The conical-ended borehole technique and hemispherical-ended borehole technique are proposed, for the accurate stress measurement within a rock mass. Theory of stress tensor determination and in situ measurement system are presented with successful case examples, and the characteristics of stress distribution within rock masses are examined by the multiple times measurement in a single borehole. Subsequently, the problem in relation to the numerical approach for cavern designing is discussed on the basis of the dependency of the stress discontinuity on the geological discontinuities and so on.

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Effect of Geometrical Discontinuity on Ductile Fracture Initiation Behavior under Static Leading

  • An, G.B.;Ohata, M.;Toyoda, M.
    • International Journal of Korean Welding Society
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    • v.3 no.1
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    • pp.51-56
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    • 2003
  • It is important to evaluate the fracture initiation behaviors of steel structure. It has been well known that the ductile cracking of steel would be accelerated by triaxial stress state. Recently, the characteristics of critical crack initiation of steels are quantitatively estimated using the two-parameters, that is, equivalent plastic strain and stress triaxiality, criterion. This study is paid to the fundamental clarification of the effect of notch radius, which can elevate plastic constraint due to heterogeneous plastic straining on critical condition to initiate ductile crack using two-parameters. Hense, the crack initiation testing were conducted under static loading using round bar specimens with circumferential notch. To evaluate the stress/strain state in the specimens was used thermal elastic-plastic FE-analysis. The result showed that equivalent plastic strain to initiate ductile crack expressed as a function of stress triaxiality obtained from the homogeneous specimens with circumferential notched under static loading. And it was evaluated that by using this two-parameters criterion, the critical crack initiation of homogeneous specimens under static loading.

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Study for Accessment of Structural Stability of SAS Reactor (SAS 반응기의 구조 안전성 평가 연구)

  • 이은우;정의동;김윤춘;김종배
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1995.10a
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    • pp.43-49
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    • 1995
  • Sasol Advanced Synthol Reactor was divided into two chambers by grid plate perforated with diffuser holes. The reactor has high stress level beacuse of membrane stress due to internal pressure, thermal stress due to temperature difference and local stress due to structural discontinuity at the juncture of grid plate and shell. Moreover, geometric nonlinear behaviors may appear in the grid plate because of pressure difference between two chambers. In order to survey the stress level and geometric nonlinear behaviors around grid plate, heat transfer analysis, linear static analysis and geometric nonlinear analysis were performed using NISA II developed by EMRC. This paper demonstrates the result of accessment for linear static and geometric nonlinear analysis under various load combinations.

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