• Title/Summary/Keyword: 피로균열 성장률

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

  • Chang, Dong Il;Kyung, Kab Soo;Cho, Kwang Hyun;Hong, Sung Wook
    • Journal of Korean Society of Steel Construction
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    • v.11 no.4 s.41
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    • pp.339-350
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    • 1999
  • In this study, blowholes, a kind of solid defects, were intentionally introduced in transverse butt-welded joints which are widely used for the connection of main members in steel structures to evaluate the fatigue characteristics of these joints with blowholes according to the difference of the size and shape of blowholes, and a series of tests were performed. Static test results proved that the static strength of these joints with blowholes was not affected by their size and shape. From the fatigue test results on these joints with blowholes, the size and shape of blowholes inside the weld metals were strongly affected in fatigue strength, and we suggested the relationship between fatigue strength and their size and shape quantitatively. Also, Using the relationship of fatigue crack growth rate and stress intensity factor range, the fatigue life of transverse butt-welded joints with blowholes can be estimated properly.

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

  • 권종완;양현태
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.11 no.3
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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.

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

  • Cho, Hwankee;Hwang, Jungsun
    • Journal of Aerospace System Engineering
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    • v.1 no.1
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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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Variation of Surface Crack Shape in Pressure Vessel Materials (압력용기 소재에서의 표면균열의 형상변화)

  • 허용학;이주진;이해무
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.3
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    • pp.617-623
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    • 1990
  • Cracks present in pressure vessels have been reported to be mostly semi-elliptic surface cracks. The fatigue crack growth rates(FCGR) of surface cracks in the pressure vessel materials, API5A-K55 and SPV 500, used in this study were showed to be different depending on the direction of propagation of the surface crack. An equation for the prediction of the shape change of the surface crack was obtained by combining the Paris' relations for each direction of surface crack extension and agreed well with the experimental data. And also FGGR in both materials were evaluated and prediction of the shape change of surface crack were made using averaged stress intensity factor.

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

  • 서창민;김영호;권오헌
    • Journal of Ocean Engineering and Technology
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    • v.6 no.1
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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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Fatigue Life Evaluation of Turbine Shaft Using Applied Shaft Stress (회전체 스트레스 정보를 이용한 터빈 축 피로수명 평가)

  • Jin, Byeong Kyou;Park, Ki Beom;Chai, JangBom
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.4
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    • pp.437-442
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    • 2014
  • The equipment or with a constant torque and a variable stress due to axial vibration such as the turbine-generator system in nuclear power plant show the fatigue fracture behavior. Thus this study whoul aim to measure the torsional stress and analyze the fatigue fracture behavior. To achieve this, we manufactured the equipment similar with turbine-generator system and applied various torsional vibration stress due to external load. In particular, the evaluation was conducted with the existing evaluation methods of the fatigue behavior of known stress-life, strain-life, crack growth assessment methods. With increasing the external load and independent methods tends to decrease the fatigue life was confirmed up to 10 times in 5 kV external load compared to without external load.

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

  • Lee Jin-Kyung;Park Young-Chul;Lee Kyu-Chang;Lee Sang-Pill;Cho Youn-Ho;Lee Joon-Hyun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.10 s.241
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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.

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

  • Song, Sam-Hong;Kim, Cheol-Woong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.3
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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.

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

  • 김덕중
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 1997.10a
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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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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 - (원공노치 인근에 발생한 결함의 위치변화가 균열성장률(da/dN) 및 응력확대계수범위(δK)의 관계에 미치는 영향 - 단일재 알루미늄과 Al/GFRP 적층재의 피로거동 비교 -)

  • Kim, Cheol-Woong;Ko, Young-Ho;Lee, Gun-Bok
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.3 s.258
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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.