• Title, Summary, Keyword: 균열조사

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질소 이온빔을 이용한 인코넬690의 기계적 특성 변화 연구

  • 홍인석;황용석
    • Proceedings of the Korean Nuclear Society Conference
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    • pp.118-122
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    • 1997
  • 차세대 원자력발전소 증기발생기 전열관 재료로 채택된 니켈기저합금으로 기존 전열관 재료인 인코넬600에 비해 고온 고압 조건에서 응력부식균열에 강한 장점을 가진 합금인 인코넬690 시료에 최대 에너지 120 keV의 질소 이온빔을 조사하여 이 재료의 기계적 특성 변화를 관측하였다. 특성 시험으로는 표면 경화를 관찰하기 위한 미세 경도 시험을 수행하여 미세 경도 증가를 확인하였다 아울러 표면 경화가 피로 특성에 미치는 영향을 관찰하기 위해 피로 균열 전파 시험을 수행하여 이온 주입으로 인한 표면 경화가 피로 균열 전파를 촉진시킴을 관찰하였다.

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Weld Cracking of High Strength Al-Zn-Mg Alloy Weldment (용접구조용 7000 계열 고장력 Al-Zn-Mg 합금의 용접특성과 용접균열에 관한 고찰)

  • 김환태;황선효;남수우
    • Journal of Welding and Joining
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    • v.12 no.1
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    • pp.28-37
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    • 1994
  • 본 소고에서는 Al-Zn-Mg 계통의 고강도 알루미늄합금의 제조과정에서 실시하는 열처리 공정을 통해 얻어지는 시효경화 효과, 합금원소 첨가에 따른 석출물의 생성과 이에 따른 석출경화 효과와 용착금속의 응고균열 발생과의 상호관계를 조사하고 용접열영향부의 용질원자 확산과 입계의 liquid film에 의한 액화(liquation) 균열의 생성을 분석하여 설명하고자 한다.

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Study on Cracking Causes and Patterns in Median Barrier and Guardrail Concrete in RC Bridge (콘크리트 교량 방호벽의 균열원인 및 패턴 분석에 대한 연구)

  • Choi, Se-Jin;Choi, Jung-Wook;Kwon, Seung-Jun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.18 no.5
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    • pp.19-26
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    • 2014
  • Concrete guide rail and median barrier are an attached RC member, however they are vulnerable to cracking due to slip form construction and large surface of member. In this study, causes and pattern of cracking are analyzed through assessment and NDT (Non-Destructive Technique) evaluation for concrete guide rail and median barrier on highway structure. For this work, analysis on drying shrinkage and hydration heat are performed considering installation period, and plastic shrinkage is also analyzed considering their environmental conditions. From the evaluation, plastic settlement around steel location, drying/ plastic shrinkage, and aggregate segregation are inferred to be the main causes of cracking in the structures. The crack causes and patterns are schematized and techniques of crack-control are suggested. Furthermore concrete guide rail/ median barrier in the bridge on the sea are vulnerable to cracking at early age so that special attentions should be paid at the stages of material selection and construction.

Numerical Computation of Dynamic Stress Intensity Factors in Axisymmetric Problems (축대칭 문제에서의 동적 응력확대계수의 계산)

  • 이성희;심우진
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.16 no.2
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    • pp.207-216
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    • 2003
  • In this paper, the finite element method for the elastodynamic axisymmetric fracture analysis is presented in matrix form through the application of the Galerkin method to the time integral equations of motion with no inertia forces. Isoparametric quadratic quadrilateral element and triangular crack tip singular elements with one-quarter node are used in the mesh division of the finite element model. To show the validity and accuracy of the proposed method, the infinite elastic medium with the penny shaped crack is solved first and compared with the analytical solution and the numerical results by the finite difference method and the boundary element method existing in the published literatures, and then the dynamic stress intensity factors of solid and hollow cylinders of finite dimensions haying penny-shaped cracks and internal and external circumferential tracks are computed in detail.

Analysis of the Effect of Pavement Crack Depth of the Cavity Management Grade (포장 균열 깊이가 공동 관리 등급에 미치는 영향 분석)

  • Park, Jeong Jun
    • Journal of the Society of Disaster Information
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    • v.16 no.3
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    • pp.449-457
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    • 2020
  • Purpose: The Seoul Metropolitan Government classifies the cavity risks into emergency, priority, general, and observation grades in consideration of the cavity size, asphalt pavement thickness, and pavement depth based on the cavity management grade criteria of Seoul. In this study, the depth of cracking was measured at 17 cracks identified by checking the pavement condition of the cavity at 265 cavities found in the 2019 cavity investigation service. Method: In the first phase, crack width and depth were measured using a vernier caliper, taper gauge, and depth gauge to check the cracks of the identified cavities. In the second phase, the location of the largest crack in the upper road surface was confirmed, and A.C. was drilled to further measure the crack depth. Results: As a result, the cavity management level was raised in nine of the 17 test cavity identified. Therefore, in case of emergency and priority recovery, the grade should be adjusted according to the depth of pavement crack and the thickness of residual A.C. pavement. Conclusion: In the case of cracks in the upper part of the cavity, the crack progression must be determined through the perforation and the remaining asphalt concrete thickness must be determined to determine the cavity grade.

A Study on the Safe Blast Design to Increase Slope Stability (발파진동이 사면에 미치는 영향과 안전설계에 관한 연구)

  • 안명석;류창하;박종남;권중남
    • Explosives and Blasting
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    • v.19 no.1
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    • pp.85-92
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    • 2001
  • 본 논문에서는 암굴착시 발파에 의한 암반사면의 균열방지 및 사면안정 재고를 위하여 대 구-포항간 고속도로 건설현장에서 시험발파를 실시하고 그 결과를 분석하여 천공깊이별 안전 발파패턴을 제시하였다. 또한 현지 탄성파 속도를 측정하여 발파에 의해 암반에 미치는 균열상태를 조사한 결과 탄성파속도의 감소가 40 ∼ 53%로서 암반 중에 균열을 발생시킨 것으로 나타났다. 발파진동 계측결과를 분석하여 암반에 균열을 일으킬 수 있는 진동속도 기준을 설정하여 균열권 범위를 추정하였으며 사면의 기하학적 형상을 고려하여 손상대를 최소화 할 수 있는 적정 안전설계 패턴을 제시하였다.

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Viscoelastic Analysis for Behavior of Edge Cracks at the Bonding Interface of Semiconductor Chip (반도체 칩 접착 계면에 존재하는 모서리 균열 거동에 대한 점탄성 해석)

  • 이상순
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.14 no.3
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    • pp.309-315
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    • 2001
  • The Stress intensity factors for edge cracks located at the bonding interface between the elastic semiconductor chip and the viscoelastic adhesive layer have been investigated. Such cracks might be generated due to stress singularity in the vicinity of the free surface. The domain boundary element method(BEM) has been employed to investigate the behavior of interface stresses. The overall stress intensity factor for the case of a small interfacial edge crack has been computed. The magnitude of stress intensity factors decrease with time due to viscoelastic relaxation.

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A Numerical Study of Hydraulic Fractures Propagation with Rock Bridges (Rock bridges를 고려한 수치 해석적 수압파쇄 균열거동 연구)

  • 최성웅
    • Proceedings of the Korean Society for Rock Mechanics Conference
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    • pp.201-210
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    • 2000
  • Rock bridge in rock masses can be considered as one of several types of opening-mode fractures, and also it has been known to have a great influence on the stability of structures in rock mats. In the beginning of researching a rock bridge it used to be studied only in characteristics of its behavior, as considering resistance of material itself. However the distribution pattern of rock bridges, which can affect the stability of rock structures, is currently researched with a fracture mechanical approach in numerical studies. For investigating the effect of rock bridges on the development pattern of hydraulic fractures, the author analyzed numerically the stress state transition in rock bridges and their phenomena with a different pattern of the rock bridge distributons. From the numerical studies, a two-crack configuration could be defined to be representative of the most critical conditions for rock bridges, only when cracks are systematic and same in their length and angle. Moreover, coalescence stresses and onset of propagation stresses could be known to increase with decreasing s/L ratio or increasing d/L ratio. The effect of pre-existing crack on hydraulic fracturing was studied also in numerical models. Different to the simple hydraulic fracturing modeling in which the fractures propagated exactly parallel to the maximum remote stress, the hydraulic fractures with pre-existing cracks dial not propagate parallel to the maximum remote stress direction. These are representative of the tendency to change the hydraulic fractures direction because of the existence of pre-existing crack. Therefore s/L, d/L ratios will be identical as a function effective on hydraulic fractures propagation, that is, the $K_{I}$ vague increase with decreasing s/L ratio or increasing d/L ratio and its magnification from onset to propagation increases with decreasing s/L ratio. The scanline is a commonly used method to estimate the fracture distribution on outcrops. The data obtained from the scanline method can be applied to the evaluation of stress field in rock mass.s.

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Drying Shrinkage and Cracking Resisting Performance of Eco-cement Concrete mixing Fly-ash (플라이 애쉬를 혼입한 에코시멘트 콘크리트의 건조수축 및 균열저항 특성)

  • Yoo, Kwan-Jong;Seo, Tae-Seok;Choi, Chang-Sik
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.409-410
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    • 2009
  • The eco-cement concrete using fly-ash was produced for the improvement of the compressive strength of the eco-cement concrete under the long term age, and compressive strength test, drying shrinkage test, uniaxial restraint shrinkage cracking test, and bond test were carried out. In this study, the cracking resistance performance was investigated.

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Fatigue Behavior of Before-and-After Penetration of Aluminium Plate with Long Surface Crack (긴 균열을 갖는 알루미늄판재의 관통전후 피로거동)

  • Nam Ki-Woo;Lee Jong-Rark;Ahn Seok-Hwan
    • Journal of the Korean Institute of Gas
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    • v.3 no.1
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    • pp.1-7
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    • 1999
  • Fatigue behavior of before-and-after penetration was examined experimentally using surface pre-cracked specimens of aluminium alloy 5083-0. The fatigue crack shape before penetration is almost semicircular, and the measured aspect ratio is larger than the value obtained by calculation using K values proposed by Newman-Raju. It is found that the crack growth behavior on the back side after penetration is unique and can be divided into three stages. By using a crack propagation rule in case of long surface crack, the change in crack shape after penetration can be evaluated quantitatively.

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