• 제목/요약/키워드: Crack Examination

검색결과 104건 처리시간 0.026초

Examination on Fatigue Limit and Crack Growth Characteristic of SBHS700 Base Metal

  • Ono, Yuki;Kinoshita, Koji
    • 국제강구조저널
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    • 제18권4호
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    • pp.1098-1106
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    • 2018
  • The object of this study is to clarify fatigue limit and fatigue crack growth characteristic of SBHS700 base metal which is 780 MPa class steel. This study carried out the fatigue tests of SBHS700 base metal containing different defect size, and the fatigue limit was compared with that of the conventional steel. Test results indicate that the fatigue limit increased with decrease initial defect size, and can be precisely evaluated by using ${\sqrt{area}}$ parameter model. This paper also presents that crack growth characteristic was almost the same as that of the conventional steel from the observation of striations by using Scanning electron microscope and length of beach marks.

증기발생기 전열관 2차측 응력부식균열의 실험실적 모사 방법 (Laboratorial technique for fabrication of outer diameter stress corrosion cracking on steam generator tubing)

  • 이재민;김성우;황성식;김홍표;김홍덕
    • Corrosion Science and Technology
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    • 제13권3호
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    • pp.112-119
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    • 2014
  • In this work, it is aimed to develop the fabrication method of axial stress corrosion cracking (SCC) defects having various sizes, on the outer diameter surface of the steam generator (SG) tubings. To control the length of the artificial SCC defect, the specific area of the SG tubing samples was exposed to an acidic solution after a sensitization heat treatment. During the exposure to an acidic solution, a direct current potential drop (DCPD) method was adopted to monitor the crack depth. The size of the SCC defect was first evaluated by an eddy current test (ECT), and then confirmed by a destructive examination. From the comparison, it was found that the actual crack length was well controlled to be similar to the length of the surface exposed to an acidic solution (5, 10, 20 or 30 mm in this work) with small standard deviation. From in-situ monitoring of the crack depth using the DCPD method, it was possible to distinguish a non-through wall crack from a through wall crack, even though the depth of the non-through wall crack was not able to be precisely controlled. The fabrication method established in this work was useful to simulate the SCC defect having similar size and ECT signals as compared to the field cracks in the SG tubings of the operating Korean PWRs.

동적하중하에서의 강도적 불균질재의 연성크랙 발생한계의 해석적 검토 - 강도적 불균질 및 동적부하의 영향에 의한 연성크랙 발생조건 (제 2 보) - (Analytical Examination of Ductile Crack Initiation with Strength Mismatch under Dynamic Loading - Criterion for Ductile Crack Initiation Effect of Strength Mismatch and Dynamic Loading (Report 2) -)

  • 안규백;;;방한서
    • Journal of Welding and Joining
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    • 제21권7호
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    • pp.49-58
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    • 2003
  • It has been well known that ductile fracture of steel is accelerated by triaxiality stresses. The characteristics of ductile crack initiation in steels are evaluate quantitatively using two-parameter criterion based on equivalent plastic strain and stress triaxiality. Recently, the characteristics of critical crack initiation of steels are quantitatively estimated using the two-parameter, that is, equivalent plastic strain and stress triaxiality, criterion. This study is paid to the fundamental clarification of the effect of geometrical heterogeneity and strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on critical condition to initiate ductile crack using two-parameter. Then, the crack initiation testing were conducted under static and dynamic loading. To evaluate the stress/strain state in the specimens especially under dynamic loading, thermal elastic-plastic dynamic FE-analysis considering the temperature rise was used. The result showed that the critical global strain to initiate ductile fracture in specimens with strength mismatch under various loading rate cu be estimated based on the local criterion, that is two-parameter criterion obtained on homogeneous specimens under static tension, by mean of FE-analysis taken into account accurately both strength mismatch and dynamic loading effects on stress/strain behavior.

스프링강의 피로크랙 진전거동에 미치는 압축잔류응력의 영향 (A Study on The Effect of Compressive Residual Stress on fatigue Crack Propagation Behavior of Spying Steel)

  • 박경동;정찬기
    • 대한기계학회논문집A
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    • 제27권1호
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    • pp.200-207
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    • 2003
  • In this paper, the effect of the compressive residual stresses which were obtained under the various shot velocities of shot balls on the fatigue behaviors of a spring steel, were investigated. The examination of CT specimen test were executed with the materials(JISG SUP9) which are being commonly used for the springs of automotive vehicles. As a result, the optimal shot velocity of shot balls were acquired considering the peak values of the compressive residual stresses on the surface of specimen and effect on the speed of the fatigue crack propagation da/dN in stage II and the threshold stress intensity factor range Δ$K_{th}$ in stage I. Also the material constant C and the crack propagation index m in the formula of paris law da/dN= C $({\Delta}K^m)$ were suggested in this work to estimate the dependency on the shot velocity.

강교용 박스거더의 용접예열 온도 선정에 관한 연구 (Determination of Preheating Temperature for Box Girder Welding)

  • 조재훈;문승재;유호선
    • 플랜트 저널
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    • 제7권1호
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    • pp.49-55
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    • 2011
  • This study analyzed causes and status of cracks to suggest preventives for welding cracks generated on fillet welding zone of atmosphere corrosion resisting steel box girder. Penetrant testing, a sort of non-destructive testing, was conducted for inspection of crack status on welding zone. As a result of test, welding cracks were found on the point of start, center and end to fillet welding zone of 32 mm-thickness. The result of carbon equivalent composition of materials was 0.452%. According to welding specification, to preheat prevent welding crack, preheat temperature of $100{\sim}200^{\circ}C$ should be kept before welding execution. It was failed to keep preheat temperature because it had been executed on winter season and the structure of box girder had wide heat transfer area. As a result of examination of time varying preheating temperature of 32mm-thickness material, it was understood that preheat temperature of above $230^{\circ}C$ on both 130mm-long sides of welded joint can prevent welding crack.

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중수로핵연료 봉단마개 용접부의 기계적 특성과 초음파 시험 (Mechanical Strength and Ultransonic Testing of End Cap Welds in Pressurized Heavy Water Reactor Fuel)

  • 이정원;최명선;정성훈;고진현
    • Journal of Welding and Joining
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    • 제9권4호
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    • pp.60-68
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    • 1991
  • The weld quality of end cap welds in Pressurized Heavy Water Reactor (PHWR) Fuel is extremely important for the fuel performance in the nuclear reactor. The quality of resistance upset welds is currently evaluated mainly by the metallographic examination although it reveals only two weld cross-sections in a circumference welds. This investigation was, firstly, carried out to determine whether the ultrasonic examination would be applied to detect weld defects in the end cap welds and, secondly, to measure the mechanical strength of upset butt welds as a function of phase shift percentage. The major results obtained in this study are as follows: 1. The weld current and amount of upset shrinkage linearly increased with increasing the phase shift percentage. 2. Above the phase shift 55%, the defects in the welds were completely eliminated with increasing the phase of sound weld was over the thickness of cladding tube. 3. The ultrasonic testing well detected such defects in the end cap welds as upset external crack, upset split, corner crack and irregular weld flash comparing with the results of metallography. 4. The micro-fissure in the corner of the end cap welds was reliably detected by ultrasonic testing. 5. The mechanical strength in the welds increased with increasing phase shift percentage but the fracture did't occur in the welds above 55%.

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미세균열이 콘크리트의 염소이온 침투에 미치는 영향: 현상학적 모델 (Effect of Micro-Cracks on Chloride Ions Penetration of Concrete: Phonomenological Model)

  • 윤인석
    • 콘크리트학회논문집
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    • 제19권1호
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    • pp.57-65
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    • 2007
  • 지난 수년간 콘크리트의 염소이온 침투와 유관되어 실험 방법론 및 해석적 모델 기법의 개발에 많은 발전이 있어 왔다. 그러나 실제 콘크리트 구조물에는 다소의 균열이 존재하며 이는 장기 내구성에 큰 영향을 줄 수 있음에도 불구하고 대부분의 연구들은 비균열의 콘크리트를 대상으로 연구되어 온 문제점이 있었으며 균열이 존재하는 콘크리트의 염소이온 침투에 대한 연구는 매우 드문 실정이다. 염소이온 침투에 대한 균열폭의 임계치는 유지관리 차원에서 필요하지만, 대부분 콘크리트 코드는 사용성의 견지에서 허용 균열폭을 보편적인 값 0.3mm로 제안하고 있을 뿐, 염소이온 침투 및 내구성의 견지에서 임계 균열폭에 대한 규정도 부재한 실정이다. 이미 제안된 값도 연구자들마다 상이하여 논란의 여지가 있다. 본 연구는 임계 균열폭의 도출을 목적으로 균열이 콘크리트의 염소이온 침투에 미치는 영향을 고찰하였다. 실험적 방법으로 다양한 균열폭과 균열 깊이를 실험 변수로 하여 급속 염소이온 침투 실험 (RCMT)를 행하였다. 한편, 임계 균열폭이 갖는 공학적 의미를 설명하고자, 균열폭에 따른 염소이온 침투의 현상학적 모델이 제안되었다. 즉, 균열된 콘크리트는 3 구간으로 나누어지며 내부 안쪽으로 들어갈수록 확산자유 영역, 확산경화 영역, 순수 확산 영역의 3가지 구간이 존재한다. 이는 균열폭에 따른 염소이온 확산계수를 산출하기 위한 해석적 방법론의 개발에 이용될 수 있을 것으로 사료된다.

항공기용 초고장력강(300M) 부품의 가공변질층과 응력부식균열에 관한 연구 (A Study of the Affected Layer and Stress Corrosion Crack of Ultra-high-strength Steel (300M) for Aircraft Parts)

  • 안진우;김태환
    • 한국기계가공학회지
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    • 제19권4호
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    • pp.1-8
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    • 2020
  • Mechanical components that support structures in aerospace and power generation industries require high-strength materials. Particularly, in the aerospace industry, aluminum alloys, titanium alloys, and composite materials are increasingly used due to their high maneuverability and durability to withstand low temperature extreme environments; however, ultra-high-strength steel is still used in key components under heavy loads such as landing gears. In this paper, the fault cause analysis and troubleshooting of aircraft parts made of ultra-high-strength steel (300M) broken during normal operation are described. To identify the cause of the defect, a temporary inspection of the same aircraft was performed, and material testing, non-destructive inspection, microstructure examination, and fracture area inspection of the damaged parts were performed. Fracture analysis results showed that a crack in the shape of a branch developed from the tool mark in the direction of the intergranular strain. Based on the results, the cause of fracture was confirmed to be stress corrosion.

실시간 레일절손 모니터링 시스템의 현장 적용에 관한 연구 (A Study on the Field Application of Real-Time Monitoring System Detecting the Broken Rail)

  • 최시행;고광남;정수영;이희성
    • 한국철도학회:학술대회논문집
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    • 한국철도학회 2011년도 춘계학술대회 논문집
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    • pp.1399-1406
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    • 2011
  • As a result of the examination analyzed loop type of Detecting the Broken Rail Monitoring System as a part of prevention of train derailment, installed in the Seoul Metro No. 2 subway line 98.51m section which is Samsung to Seolleung, we found that it is possible to detect crack location(Thermit welding: 48.18m) within the margin of error of ${\pm}1m$ accurately As analysis of the first day, third day, fifty day, and seventh day periodically, we found that Fresnel reflection happened where the crack location 48.18m. However other 3 branches show loss by bending of optical cable(spread reflection from the outside impact).

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기체분리용 세라믹 복합분리막의 개발: III. 기체투과 모델에 의한 막의 특성 규명 (Development of Ceramic Composite Membranes for Gas Separation: III. Examination of Membrane Characteristics by the Gas Permeation Model)

  • 현상훈;윤성필;강범석
    • 한국세라믹학회지
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    • 제29권11호
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    • pp.905-911
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    • 1992
  • Model equations for the gas permeation through a ceramic composite membrane were derived for examining the existence of crack, the reproducibility, and the microstructural properties of composite membranes. From the results of analyzing the nitrogen permeability data through alumina-tube supported TiO2 and SiO2 composite membranes, the extent of cracking, and the formation and structure of membrane top-layers were modelled. It was proved that the crack-free and reproducible composite membranes could be easily prepared only by the pore-filled coating within pores of the support in the sol-gel coating process.

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