• 제목/요약/키워드: 피로균열 성장률

검색결과 45건 처리시간 0.022초

블로우홀을 가진 횡방향 맞대기 용접부의 피로특성에 관한 연구 (A Study on the Fatigue Characteristics of Transverse Butt-Welded Joints containing Blowholes)

  • 장동일;경갑수;조광현;홍성욱
    • 한국강구조학회 논문집
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    • 제11권4호통권41호
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    • pp.339-350
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    • 1999
  • 이 연구에서는 강교량 주부재의 연결에 주로 사용되는 횡방향 맞대기 용접부를 대상으로 입체결함의 일종인 블로우홀을 인위적으로 도입하고 블로우홀의 크기 및 형상에 따른 피로특성을 정량적으로 평가하기 위해서 일련의 실험을 실시하였다. 정적실험결과 블로우홀을 가진 횡방향 맞대기 용접부의 정적강도는 블로우홀의 크기 및 형상에 관계없이 일정한 경향을 나타내었다. 피로실험결과 블로우홀을 가진 횡방향 맞대기 용접부의 피로강도는 용접루트부 내부에 존재하는 블로우홀의 기하학적 형상이나 결함률에 크게 영향을 받으므로 이로부터 결함률과 피로강도 사이의 상관관계를 정량적으로 규명하였다. 또한 피로균열성장속도와 응력확대계수범위 사이의 관계로부터 블로우홀을 가진 횡방향 맞대기 용접부의 피로수명을 정확하게 산정할 수 있었다.

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단일 및 혼합모드하에서 304스테인리스강의 피로균열 진전속도와 방향특성 (Fatigue Crack Growth Rates and Directions in STS304 under Mode I and Mixed Mode)

  • 권종완;양현태
    • 한국공작기계학회논문집
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    • 제11권3호
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    • pp.102-109
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    • 2002
  • The fatigue crack growth under mixed mode condition has been discussed within the scope of linear fracture mechanics such as maximum tangential stress, maximum tangential principal stress and minimum strain energy density. The purpose of this study is to investigate the characteristics of fatigue test crack growth in 304 stainless steel under mixed node. The fatigue test results carried out by using inclined pre-crack specimens was compared to both of the theoretical predictions of the criteria, maximum tangential stress and stain energy density. As difference from theoretical analysis, the transition region from mixed mode to mode I appeared in the fatigue test. There is deep relationship between the angle of slanted pre-crack and transition. Therefore, as applying the different stress intensity factor to each node I+II and mode I, the directions and rates of fatigue crack growth are evaluated more accurately under mixed mode.

알루미늄 합금 판재에서 예비압입에 의한 피로수명의 연장효과 분석 (Analysis of the Extension Effects of Fatigue Life by Pre-Indentation in Aluminum Alloy Plates)

  • 조환기;황정선
    • 항공우주시스템공학회지
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    • 제1권1호
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    • pp.45-52
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    • 2007
  • This paper analyzed the extension effects of fatigue life and the application of pre-indentation in aircraft structural material such as aluminum alloys. The test specimen used the thin sheet of aluminum alloy with a single-edged notch. The experiments were conducted after making the pre-crack under a constant amplitude loading. As the fatigue life extension technique, the pre-indentation making an indent on the predicted path of crack propagation was applied. The work presented here discussed about a proper mathematical relation between crack growth rate and the range of stress intensity factor and about the generalization of crack growth mechanism with large retardation effect. A technique to enhance the applicability of pre-indentation if also mentioned.

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압력용기 소재에서의 표면균열의 형상변화 (Variation of Surface Crack Shape in Pressure Vessel Materials)

  • 허용학;이주진;이해무
    • 대한기계학회논문집
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    • 제14권3호
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    • pp.617-623
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    • 1990
  • 본 연구에서는 표면방향과 깊이 방향으로 표면균열의 피로성장률이 다르게 나 타나고 있는 경우의 표면균열 형상변화를 표면균열의 균열 열림을 고려하여 해석할 수 있는 식이 수정 제안되었으며, 압력용기 소재에서 측정된 표면균열의 형상변화와 본 연구에서 제안된 형상 변화식에 의한 예측과 비교 분석하였다. 또한 균열 성장과 형 상변화를 평균 응력강도계수에 대해 분석하였고 다른 표면균열 형상 변화식들에 의한 표면균열 형상변화해석이 같이 비교 검토되었다.

차원해석법에 의한 고온피로 파괴 모델의 기초적 연구 (A Basic Study on Fatigue Fracture Model at Elevated Temperatures by the Dimensional Analysis Method)

  • 서창민;김영호;권오헌
    • 한국해양공학회지
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    • 제6권1호
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    • pp.105-112
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    • 1992
  • The main purpose of this study is to derive a law of fatigue crack growth rate in the region of elastic or elasto-plastic fracture mechanics at elevated temperatures through the application of dimensional analysis. An equation of elasto-plastic fatigue crack growth rate at elevated temperatures appeared a new Arrhenius type equation containing J-integral range and absolute temperature. The elastic or elasto-plastic crack growth rate equation shows a fairly good agreement with the experimental results for Cr-Mo-V rotor steel and Hastelloy-X alloy in the comparatively wide temperature ranges.

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회전체 스트레스 정보를 이용한 터빈 축 피로수명 평가 (Fatigue Life Evaluation of Turbine Shaft Using Applied Shaft Stress)

  • 진병규;박기범;채장범
    • 대한기계학회논문집A
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    • 제38권4호
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    • pp.437-442
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    • 2014
  • 원자력 발전소의 터빈-발전기 시스템과 같이 일정한 토크와 함께 축 진동에 의한 가변 응력이 인가되는 부재의 경우 비틀림 응력에 의한 피로 파괴 거동을 보인다. 따라서 본 연구에서는 터빈-발전기의 터빈 축에 인가하는 비틀림 응력을 측정하고 응력에 의해 발생하는 피로 파괴 거동을 분석하는 것을 목적으로 하였다. 이를 위해 터빈-발전기 시스템과 같은 실험 장치를 제작하고 임의의 부하를 인가하여 다양한 비틀림 응력에 대한 피로 파괴 거동을 평가하였다. 특히 기존의 알려진 피로 거동 평가 방법인 응력-수명, 변형률-수명, 균열성장 평가 방법을 동시에 적용하여 평가를 진행하였다. 부하의 크기가 증가하면서 평가 방법과 무관하게 피로 수명이 감소하는 경향이 확인하였으며 5 kV 부하 인가 시 최대 10배의 피로 수명의 감소가 발생하였다.

TiNi/A16061 형상기억복합재료의 피로균열진전에 대한 냉간압연효과 (Effect of Cold Rolling on Fatigue Crack Propagation of TiNi/A16061 Shape Memory Composite)

  • 이진경;박영철;이규창;이상필;조윤호;이준현
    • 대한기계학회논문집A
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    • 제29권10호
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    • pp.1315-1320
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    • 2005
  • TiNi alloy fiber was used to recover the original shape of materials using its shape memory effect. The shape memory alloy plays an important role within the metal matrix composite. The shape memory alloy can control the crack propagation in metal matrix composite, and improve the tensile strength of the composite. In this study, TiNi/A16061 shape memory alloy(SMA) composite was fabricated by hot press method, and pressed by a roller for its strength improvement. The four kinds of specimens were fabricated with $0\%,\;3.2\%,\;5.2\%\;and\;7\%$ and volume fraction of TiNi alloy fiber, respectively. A fatigue test has performed to evaluate the crack initiation and propagation for the TiNi/A16061 SMA composite fabricated by かis method. In order to study the shape memory effect of the TiNi alloy fiber, the test has also done under both conditions of the room temperature and high temperature. The relationship between the crack growth rate and the stress intensity factor was clarified for the composite, and the cold rolling effect was also studied.

하이브리드 복합재료의 섬유배향각이 피로균열 및 층간분리 거동의 관계에 미치는 영향 (The Effect of Fiber Stacking Angle on the Relationship Between Fatigue Crack and Delamination Behavior in a Hybrid Composite Materials)

  • 송삼홍;김철웅
    • 대한기계학회논문집A
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    • 제28권3호
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    • pp.281-288
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    • 2004
  • The hybrid composite material (Al/GFRP laminates) are applied to the fuselage and wing in a aircraft. Therefore, Al/GFRP laminates suffer from the cyclic bending moments. This study was to evaluate the effect of fiber stacking angle on the fatigue crack propagation and delamination behavior using the relationship between crack growth rate (da/dN) and stress intensity factor range (ΔK) in Al/GFRP laminates under cyclic bending moment. The variable delamination growth behavior in case of three different type of fiber orientations, i.e., [Al/O$_2$/Al], [Al/+45$_2$/Al] and [Al/90$_2$/Al] at the interface of Al layer and glass fiber layer was measured by ultrasonic C-scan images. As results of this study, It represent that the delamination shape should turns out to have more effective characteristics on the fiber stacking angle. The extension of the delamination zone in case of [Al/+45$_2$/Al] and [Al/90$_2$/Al] were not formed along the fatigue crack profile. The shape of delamination zone depend on fiber stacking angle and the variable type with the delamination contour decreased non-linearly toward the crack tip at the Al layer.

점 용접 너깃부에서의 변형률 측정에 의한 피로균열성장 예측 (Prediction of the Fatigue Crack Growth from Strain Measurement on Spot Welded Nugget Zone)

  • 김덕중
    • 한국공작기계학회:학술대회논문집
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    • 한국공작기계학회 1997년도 추계학술대회 논문집
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    • pp.140-145
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    • 1997
  • In case of spot-welded joints, the fatigue cracks generally originate from the weld interfaces of the neighborhood nugget tips, and propagate toward the outer surfaces of the sheets. Generally, because fatigue crack was observed in nugget around, strain gage was attached at nugget zone. Accordingly, it was very difficult to detect the generation time of fatigue crack in spot-welded joints and to measure the propagation speed of fatigue crack. We developed the non-destructive method, according to which th fatigue crack propagation rate can be quantitatively estimated by utilizing information obtained from strain gages bonded on the electrode indentations of spot welds. The results measured by real crack were compared with the data which was measured by strain gauge method in fatigue testing. And so fatigue strength was evaluated by stress intensity factor. In this study behavior of fatigue crack propagation under repeated load were considered.

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원공노치 인근에 발생한 결함의 위치변화가 균열성장률(da/dN) 및 응력확대계수범위(δK)의 관계에 미치는 영향 - 단일재 알루미늄과 Al/GFRP 적층재의 피로거동 비교 - (The Effect of Defect Location Near a Circular Hole Notch on the Relationship Between Crack Growth Rate (da/dN) and Stress Intensity Factor Range (δK) - Comparative Studies of Fatigue Behavior in the Case of Monolithic Al Alloy vs. Al/GFRP Laminate -)

  • 김철웅;고영호;이건복
    • 대한기계학회논문집A
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    • 제31권3호
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    • pp.344-354
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    • 2007
  • The objective of this study is to investigate the effect of arbitrarily located defect around the circular hole in the aircraft structural material such as Al/GFRP laminates and monolithic Al alloy sheet under cyclic bending moment. The fatigue behavior of these materials may be different due to the defect location. Material flaws in the from of pre-existing defects can severely affect the fatigue crack initiation and propagation behavior. The aim of this study is to evaluate effects of relative location of defects around the circular hole in monolithic Al alloy and Al/GFRP laminates under cyclic bending moment. The fatigue behavior i.e., the stress concentration factor($K_t$), the crack initiation life($N_i$), the relationship between crack length(a) and cycles(N), the relationship between crack growth rate(da/dN) and stress intensity factor range(${\Dalta}K$) near a circular hole are considered. Especially, the defects location at ${\theta}_1=0^{\circ}\;and\;{\theta}_2=30^{\circ}$ was strongly effective in stress concentration factor($K_t$) and crack initiation life($N_i$). The test results indicated the features of different fatigue crack propagation behavior and the different growing delamination shape according to each location of defect around the circular hole in Al/GFRP laminates.