• 제목/요약/키워드: 균열열림

검색결과 68건 처리시간 0.031초

내압이 작용하는 원주방향 관통균열 배관의 비선형 파괴역학 해석법 (An Engineering Method for Non-Linear Fracture Mechanics Analysis of Circumferential Through-Wall Cracked Pipes Under Internal Pressure)

  • 허남수;김윤재;김영진
    • 대한기계학회논문집A
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    • 제26권6호
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    • pp.1099-1106
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    • 2002
  • This paper provides engineering J-integral and crack opening displacement (COD) estimation equations for circumferential through-wall cracked pipes under internal pressure and under combined internal pressure and bending. Based on selected 3-D finite element calculations for the circumferential through-wall cracked pipes under internal pressure using the idealized power law materials, the elastic and plastic influence functions for fully plastic J-integral and COD solutions are found as a function of the normalized crack length and the mean radius-to-thickness ratio. These developed GE/EPRI-type solutions are then re-formulated based on the enhanced reference stress method. Such re-formulation not only provides simpler equations for J-integral and COD estimations, but also can be easily extended to combined internal pressure and bending. The proposed equations are compared with elastic-plastic finite element results using actual stress-strain data, which shows overall excellent agreement.

광범위 크리프 조건에 대한 관통균열 배관의 크리프 파괴역학 해석 (Creep Fracture Mechanics Analysis for Through-Wall Cracked Pipes under Widespread Creep Condition)

  • 허남수;김윤재;김영진
    • 대한기계학회논문집A
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    • 제27권6호
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    • pp.890-897
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    • 2003
  • This paper compares engineering estimation schemes of C* and creep COD for circumferential and axial through-wall cracked pipes at elevated temperatures with detailed 3-D elastic-creep finite element results. Engineering estimation schemes included the GE/EPRI method, the reference stress method where reference stress is defined based on the plastic limit load and the enhanced reference stress method where the reference stress is defined based on the optimized reference load. Systematic investigations are made not only on the effect of creep-deformation behaviour on C* and creep COD, but also on effects of the crack location, the pipe geometry, the crack length and the loading mode. Comparison of the FE results with engineering estimations provides that for idealized power law creep, estimated C* and COD rate results from the GE/EPRI method agree best with FE results. For general creep-deformation laws where either primary or tertiary creep is important and thus the GE/EPRI method is hard to apply, on the other hand, the enhanced reference stress method provides more accurate and robust estimations for C* and COD rate than the reference stress method.

${\Delta}K_{eff}$ 제어 피로 균열 진전 시험 자동화 시스템에 관한 연구 (An Automated System for Constant ${\Delta}K_{eff}$ Fatigue Crack Growth Testing through Real-time Measurement of Crack Opening Load)

  • 신성철;송지호
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집A
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    • pp.447-452
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    • 2001
  • An automated system is developed to perform fatigue crack growth tests under constant effective stress intensity factor range ${\Delta}K_{eff}$. In the system, crack length and crack opening load are measured in real-time by using the unloading elastic compliance method. The system consists of two personal computers, an analogue electrical subtraction circuit, a stepping motor, a stepping motor driver, a PIO board, and the application software used to integrate the whole system. The performance of the developed system was tested and discussed performing constant ${\Delta}K_{eff}$ crack growth tests on a CT specimen of 7075-T6 aluminum alloy. The performance of the system is found to be strongly dependent on the accuracy of measurements of crack opening load. Besides constant ${\Delta}K_{eff}$ testing, the system is expected to be successfully applied for automation of various fatigue tests.

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축방향 관통균열 배관의 새로운 탄소성 J-적분 및 COD 계산식 (New Engineering J and COD Estimation Methods for Axial Through-Wall Cracked Pipes)

  • 허남수;박영재;김윤재;김영진
    • 대한기계학회논문집A
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    • 제27권2호
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    • pp.239-246
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    • 2003
  • This paper proposes engineering estimation equations of elastic-plastic J and COD fur axial through-wall cracked pipes under internal pressure. Based on detailed 3-D FE results based on deformation plasticity, the plastic influence functions for fully plastic J and COD solutions are tabulated as a function of the mean radius-to-thickness ratio, the normalized crack length. and the strain hardening. Based on these results, the GE/EPRI-type J and COD estimation equations are proposed and validated against the 3-D FE results based on deformation plasticity. For more general application to general stress-strain laws or to complex loading, the developed GE/EPRI-type solutions are re-formulated based on the reference stress concept. Such a reformulation provides simpler equations for J and COD, which are then further extended to combined internal pressure and bending. The proposed reference stress based J and COD estimation equations are compared with elastic-plastic 3-D FE results using actual stress-strain data for Type 316 stainless steels. The FE results for both internal pressure cases and combined internal pressure and bending cases compare very well with the proposed J and COD estimations.

컨테이너선의 후 물재 용접부 취성 균열 전파에 대한 FCAW와 SAW의 비교 특성에 관한 연구 (Comparison of the Characteristics of FCAW and SAW for the Brittle Crack Propagation of Welded Parts of BCA Steel in Container Ships)

  • 최경신;이상훈;최정주
    • 한국기계가공학회지
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    • 제20권3호
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    • pp.24-32
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    • 2021
  • The size of container ships is increasing to increase the cargo loading capacity. However, container ships are limited in terms of the hull longitudinal strength. To overcome this limitation, brittle crack arrest steel can be used. This study was aimed at examining the influence of the heat input on the welding procedures of flux cored arc welding and submerged arc welding. In the experiment, the crack tip opening displacement test, which pertains to a parameter of fracture mechanics, was performed, and a 3-point bending tester was adopted. Based on the results, the crack measurement method was presented, and the stress expansion coefficient value for the pre-fatigue crack length was derived according to the heat input after the pre-cracking length was measured. It was noted that the heat input affected the crack tip opening displacement of brittle crack arrest steel.

DIC를 이용한 입자강화 복합재료의 파괴거동 평가 (Evaluation of Fracture Behavior on Particle Reinforced Composite Using Digital Image Correlation)

  • 홍상현;이정원;김재훈;이상연;박재범;정규동
    • 한국항공우주학회지
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    • 제46권7호
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    • pp.535-541
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    • 2018
  • 본 연구에서는 입자강화 복합재료의 파괴거동을 평가하기 위해 쐐기분열시험을 수행하였다. 균열 저항성을 분석하기 위해 균열선단열림변위(CTOD)와 균열선단열림각도(CTOA)를 이용하였다. 사용된 입자강화 복합재료는 특성상 온도와 하중속도에 영향을 많이 받기 때문에 다양한 온도($-60^{\circ}C{\sim}50^{\circ}C$)와 하중속도(5~500mm/min)조건에서 시험을 수행하였다. 또한 균열선단에 대한 변형률장을 분석하기 위해 디지털 이미지 상관법(DIC)을 이용하였다. 시험결과 파괴에너지는 온도가 감소할수록 증가하였으며, 하중속도가 증가할수록 균열저항성이 증가하였다.

응집 요소를 사용한 균열 진전 유한요소 해석에서 응집 법칙의 영향에 대한 연구 (A Study on the Effect of Cohesive Laws on Finite Element Analysis of Crack Propagation Using Cohesive Elements)

  • 서형석;백형찬;김현규
    • 대한기계학회논문집A
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    • 제38권4호
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    • pp.401-407
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    • 2014
  • 본 논문에서는 3점 굽힘과 이중 외팔보 문제에 대하여 응집 요소를 사용한 유한요소 균열 진전해석을 수행하고 응집 법칙의 영향을 알아보았다. 응집 요소는 ABAQUS/Standard의 사용자 서브루틴(UEL)으로 구현하였으며 응집 법칙은 다항식 형태의 응집 트랙션-열림 변위의 관계식을 사용하였고 응집 법칙의 형상에 대한 영향을 알아 보기 위하여 다항식의 계수를 변화시켰다. 동일한 파손 에너지와 응집 강도를 갖지만 다른 형상의 응집 법칙에 대한 해석을 수행하고 변위-반력 곡선을 비교하여 균열 진전 거동의 변화를 알아보았다. 또한 요소 크기에 따른 균열 진전 해석 결과의 영향을 논의하였다.

임계 CTOA조건을 이용한 파괴해석 (Fracture Analysis Based on the Critical-CTOA Criterion)

  • 구인회
    • 대한기계학회논문집
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    • 제17권9호
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    • pp.2223-2233
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    • 1993
  • An engineering method is suggested to calculate the applied load versus crack extension in the elastic-plastic fracture. The condition for an increment of crack extension is set by a critical increment of crack-up opening displacement(CTOD). The ratio of the CTOD increment to the incremental crack extention is a critical crack-tip opening angle(CTOA), assumed to be constant for a material of a given thickness. The Dugdale model of crack-tip deformation in an infinite plate is applied to the method, and a complete solution for crack extension and crack instability is obtained. For finite-size specimens of arbitrary geometry in general yielding, an approximate generalization of the Dugdale model is suggested so that the approximation approaches the small-scale yielding solution in a low applied load and the finite-element solution in a large applied load. Maximum load is calculated so that an applied load attains either a limit load on an unbroken ligament or a peak load during crack extension. The proposed method was applied to three-point bend specimens of a carbon steel SM45C in various sizes. Reasonable agreements are found between calculated maximum loads and experimental failure loads. Therefore, the method can be a viable alternative to the J-R curve approach in the elastic-plastic fracture analysis.

CrMoV 터빈로터강에서 모의 열영향부 시험편을 이용한 재열균열 민감도평가 (Evaluation of Reheat Cracking Susceptibility with Simulated Heat Affected Zones in Cr-Mo-V Turbine Rotor Steel)

  • 김광수
    • Journal of Welding and Joining
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    • 제13권1호
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    • pp.89-102
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    • 1995
  • The evaluation of reheat cracking susceptibility in CrMoV turbine rotor steel was performed using thermally simulated heat affected zones. The examinations were carried out in terms of microstructural characterization, microhardness measurement and a Charpy type notch opening three point bend test. It was found that reheat cracking susceptibility increased as the peak temperature increased. This effect was due to the combined effects of the carbide dissolution and unrestricted grain growth at 1350.deg. C peak temperature. Reheat cracking susceptibility was estimated based on microhardness measurement and prior austenite grain size. It was established that for this particular material, reheat cracking in coarse grained heat affected zone can be eliminated if the microhardness is below about 360DPH and the grain size is below about 30.mu.m. It is evident that reheat cracking susceptibility can be eliminated or reduced by carefully controlling the welding parameters such that a refined structure is produced in the coarse grained heat affected zone.

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정확한 비선형 파괴역학 해석을 위한 새로운 Ramberg-Osgood 상수 결정법 (On Relevant Ramberg-Osgood Fit to Engineering Non-Linear Fracture Mechanics Analysis)

  • 김윤재;허남수;김영진;최영환;양준석
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 춘계학술대회
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    • pp.170-177
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    • 2003
  • This paper proposes a robust method for the Ramberg-Osgood (R-O) fit to accurately estimate elastic-plastic J from engineering fracture mechanics analysis based on deformation plasticity. The proposal is based on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover, for practical applications, the method is given not only for the case when full stress-strain data are available but also for the case when only yield and tensile strengths are available. Reliability of the proposed method for the R-O fit is validated against detailed 3-D Finite Element (FE) analyses for circumferential through-wall cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels. Taking the FE J results based on incremental plasticity using actual stress-strain data as reference, the FE J results based on deformation plasticity using various R-O fits are compared with reference J values. Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed, together with its accuracy.

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