• Title, Summary, Keyword: 표면균열

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Ultrasonic evaluation of small surface fatigue cracks initiating in residual stress zone (잔류응력 영역에서 발생한 작은 피로균열의 초음파 평가)

  • Kang Kae-Myung;Kim Jin-Yeon
    • Journal of the Korean Institute of Gas
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    • v.4 no.1
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    • pp.55-62
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    • 2000
  • A surface acoustic wave method for the evaluation of small fatigue crack initiated from a pit-type surface flaw is presented. In-situ ultrasonic experiments are performed for aluminum 2024-T3 alloy samples under the fatigue test. During the fatigue test, the surface acoustic wave reflection signal from the pit and crack is measured under different hold-stress levels. From the measured and predicted surface wave reflections the depths of fully and partially open cracks are determined and results are verified by comparing with SEM fractography The crack opening behavior of the fatigue crack is evaluated from the predicted effective crack depths. The method developed in this study can be applied to monitor and characterize crack initiation and propagation from pit-type surface flaws in the early stage of fatigue life.

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A Study on the Application of Acoustic Emission for the fatigue Test of Ship Welded Structure (선박의 용접구조 피로시험에 대한 음향방출기법의 적용 연구)

  • An, Sung-Chan;Kim, Dae-Soo;Lee, Jin-Hee;Park, Jin-Soo
    • Journal of the Korean Society for Nondestructive Testing
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    • v.23 no.3
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    • pp.220-226
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    • 2003
  • This paper presents the result of an investigation on the application of the acoustic emission method to the monitoring of fatigue crack initiation, growth and track location in welded joints. Fatigue test was carried out for a typical fillet welded joint of ship structure. AE parameter such as ring down count was analyzed in time domain and crack locations were examined by source location and cluster option which is one of the functions of AE signal processor The usability of AE mettled was confirmed for the detection of the initiation and location of through crack.

Cracks in Tape Cast Oxide Laminar Composites (테이프 캐스팅 산화물 층상 복합체에서의 균열)

  • Kim, Ji-Hyun;Yang, Tae-Young;Lee, Yoon-Bok;Yoon, Seog-Young;Park, Hong-Chae
    • Journal of the Korean Ceramic Society
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    • v.39 no.5
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    • pp.484-489
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    • 2002
  • Hot-pressure sintered laminar composites with alumina/zirconia or mullite/zirconia as an outer layer and alumina/zircon (resulting in reaction-bonded mullite/zirconia during sintering) as an inner layer were fabricated by tape casting and lamination. Various forms of crack were observed in sintered laminar composites, these cracks included channel cracks in the outer layer, transverse cracks in the inner layer and interface cracks debonding interlayer. Based on detailed microscopic observations, the cracks were attributed to thermal expansion mismatch between the oxides consisting of the each layer. In particular, the interlayer and transverse cracks were confirmed in the laminates consisted of the mullite/zirconia system as the outer layers, however, those cracks were not observed in the alumina/zirconia system used. In addition, the crack propagation did not exhibit same behavior in the two kinds of outer layer when the indentation load was applied.

Investigation on Effect of Distance Between Two Collinear Circumferential Surface Cracks on Primary Water Stress Corrosion Crack Growth in Alloy 600TT Steam Generator Tubes (Alloy 600TT 증기발생기 전열관내 일렬 원주방향 표면 일차수응력 부식균열 성장에 미치는 균열 간격의 영향 고찰)

  • Heo, Eun-Ju;Kim, Jong-Sung;Jeon, Jun-Young;Kim, Yun-Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.3
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    • pp.269-273
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    • 2015
  • The study investigated the effect of the distance between two collinear circumferential surface cracks on the primary stress corrosion crack (PWSCC) growth in alloy 600TT steam generator tubes using a finite element damage analysis based on the PWSCC initiation model and macroscopic phenomenological damage mechanics approach. The damage analysis method was verified by comparing the results to the previous study results. The verified method was applied to collinear circumferential surface PWSCCs. As a result, it was found that the collinear cracks showed earlier coalescence and penetration times than the a single crack, and the times increased with the distance. In addition, it is expected that penetration may occur before coalescence of two cracks if they are more than a specific distance apart.

Surface crack propagation behavior and crack closure phenomena in 5083-H113 aluminum alloy (5083-H113 알루미늄合金의 表面균열進展擧動과 균열닫힘 現象)

  • 박영조;김정규;신용승;김영운
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.2
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    • pp.243-252
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    • 1987
  • The propagation and closure behavior of surface crack initiated at a sharply notched specimens were investigated in 5083-H113 aluminium alloy under constant amplitude of tension load by the unloading elastic compliance method. The crack shape (aspect ratio) was found to be approximately semicircular during the crack was being small and to be changed to semi-elliptical during it was being long. The propagation rate of a surface crack initiated from notch root decelerated with increasing crack length when the crack was small and then accelerated when it was large. The effect of stress ratio was large in lower .DELTA.K range, but the effective stress intensity factor range .DELTA.K$_{eff}$ was found to diminish the difference of the crack propagation rate. By considering the increase in crack closure stress with crack length and examining the microphotographs, plasticity-induced and roughness-induced crack closure mechanisms were predominant in the range of this study.y.

Dimensionality Reduced Wave Transmission Function and Neural Networks for Crack Depth Estimation in Concrete Structures (차원 축소된 표면파 투과 함수와 인공신경망을 이용한 콘크리트 구조물의 균열 깊이 평가 기법)

  • Shin, Sung-Woo;Yun, Chung-Bang
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.20 no.3
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    • pp.247-253
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    • 2007
  • Determination of crack depth in filed using the self-calibrating surface wane transmission measurement and the cutting frequency in the transmission function (TRF) is very difficult due to variations of the measurement conditions. In this study, it is proposed to use the measured full TRF as a feature for crack depth assessment. A Principal component analysis (PCA) is employed to generate a basis of the measured TRFs for various crack cases. The measured TRFs are represented by their projections onto the most significant principal components. Then artificial neural networks (NNs) using the PCA-compressed TRFs is applied to assess the crack in concrete. Experimental study is carried out for five different crack cases to investigate the effectiveness of the proposed method. Results reveal that the proposed method can be effectively used for the crack depth assessment of concrete structures.

Spectral Energy Transmission Method for Crack Depth Estimation in Concrete Structures (콘크리트 구조물의 균열 깊이 추정을 위한 스펙트럼 에너지 기법)

  • Shin, Sung-Woo;Min, Ji-Young;Yun, Chung-Bang;Popovics, John S.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.27 no.2
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    • pp.164-172
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    • 2007
  • Surface cracks in concrete are common defects that can cause significant deterioration and failure of concrete structures. Therefore, the early detection, assessment, and repair of the cracks in concrete are very important for the structural health. Among studies for crack depth assessment, self-calibrating surface wave transmission method seems to be a promising nondestructive technique, though it is still difficult in determination of the crack depth due to the variation of the experimentally obtained transmission functions. In this paper, the spectral energy transmission method is proposed for the crack depth estimation in concrete structures. To verify this method, an experimental study was carried out on a concrete slab with various surface-opening crack depths. Finally, effectiveness of the proposed method is validated by comparing the conventional time-of-flight and cutting frequency based methods. The results show an excellent potential as a practical and reliable in-situ nondestructive method for the crack depth estimation in concrete structures.

Reliability Estimation for Crack Growth Life of Turbine Wheel Using Response Surface (반응표면을 사용한 터빈 휠의 균열성장 수명에 대한 신뢰성 평가)

  • Jang, Byung-Wook;Park, Jung-Sun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.40 no.4
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    • pp.336-345
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    • 2012
  • In crack growth life, uncertainties are caused by variance of geometry, applied loads and material properties. Therefore, the reliability estimation for these uncertainties is required to keep the robustness of calculated life. The stress intensity factors are the most important variable in crack growth life calculation, but its equation is hard to know for complex geometry, therefore they are processed by the finite element analysis which takes long time. In this paper, the response surface is considered to increase efficiency of the reliability analysis for crack growth life of a turbine wheel. The approximation model of the stress intensity factors is obtained by the regression analysis for FEA data and the response surface of crack growth life is generated for selected factors. The reliability analysis is operated by the Monte Carlo Simulation for the response surface. The results indicate that the response surface could reduce computations that need for reliability analysis for the turbine wheel, which is hard to derive stress intensity factor equation, successfully.

Propagation Behavior of Inclined Surface Crack of Semi-Infinite Elastic Body under Hertzian Contact (반무한 탄성체의 헤르츠 접촉하의 경사진 표면균열의 전파거동)

  • 김재호;김석삼;박중한
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.3
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    • pp.624-635
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    • 1990
  • Analytical study based on linear fracture mechanics was conducted on propagation behavior of inclined surface crack in semi-infinite elastic body. The analytical model was assumed to be inclined surface crack under plane strain condition upon which Hertzian stress was superimposed. Supposing continuous distribution of dislocation and applying Erdogan-Gupta's method to this crack problem, the stress intensity factors $K_{I}$ and $K_{II}$) at the crack-tip were obtained for various Hertzian contact positions. Analytic results have shown that driving force for crack growth is $K_{I}$ for non-lubricated condition and $K_{II}$ for fluid and boundary lubricated condition. The coefficient of friction at the hertzian contact and crack surfaces plays an important role in predicting the direction of crack propagation. It is also found that the maximum effective stress intensity factor exists at cracks of a certain specific length depending on lubricated condition.ion.n.

The Effect of Stress Ratio on the Surface Crack Growth Behavior in 7075-T651 Aluminum Alloy (7075-T651 Al合金의 表面균열進展에 미치는 應力比의 影響)

  • 박영조;김정규;신용승;김성민
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.10 no.1
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    • pp.62-69
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    • 1986
  • Fatigue surface crack growth was studied in 7075-T651 aluminum alloy plates subjected largely to bending loads. The surface crack length and its depth were measurement by the unloading elastic compliance method. The surface crack growth rate dc/dN, on the surface and da/dN, in the depth direction were obtained by the secant method. The stress intensity factor range .DELTA.K was computed by means of Newman and Raju equation. The aspect ratio a/c was presented in form of a/c=0.815-0.853(a/T). The effect of the stress ratio on the stable surface crack growth rates under increasing .DELTA.T is larger in lower .DELTA.K, while the relation between dc/dN, da/dN and the effective stress intensity factor range .DELTA.K$_{eff}$ is weakly dependent on the stress ratio.o.