• Title, Summary, Keyword: Cracks

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Crack Closure and Growth Behavior of Short Fatigue Cracks under Random Loading (Part I : Details of crack Closure Behavior) (짧은 피로균열의 랜덤하중하의 균열닫힘 및 진전거동 (Part I: 균열닫힘 거동 상세))

  • Lee, Shin-Young;Song, Ji-Ho
    • Proceedings of the KSME Conference
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    • pp.79-84
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    • 2000
  • Crack closure and growth behavior of physically short fatigue cracks under random loading are Investigated by performing narrow- and wide-band random loading tests for various stress ratios. Artificially prepared two-dimensional, short through-thickness cracks are used. The closure behavior of short cracks under random loading is discussed, comparing with that of short cracks under constant-amplitude loading and also that of long cracks under random loading. Irrespective of random loading spectrum or block length, the crack opening load of short cracks is much lower under random loading than under constant-amplitude loading corresponding to the largest load cycle in a random load history, contrary to the behavior of long cracks that the crack opening load under random loading is nearly the same as or slightly higher than constant-amplitude results. This result indicates that the largest load cycle in a random load history has an effect to enhance crack opening of short cracks.

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Fatigue Growth Behavior of Short Cracks (짧은균열의 피로성장거동)

  • 최용식;홍성호;우흥식;한지원
    • Journal of the Korean Society of Safety
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    • v.8 no.1
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    • pp.54-58
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    • 1993
  • The fatigue growth behavior of short cracks were studied various load ratios. Computer-aided unloading elastic compliance method was employed to measure the closure and the length of short cracks. In the dc/dN-$\Delta$K relationships. the decreasing behavior of the growth rate of short cracks is due to the decrease of crack opening ratio with increasing crack length. Irrespective of load ratio. the growth rate of short cracks can be well decribed in terms of the effective stress intensity factor range $\Delta$K$_{eff}$, which is calculated on the base of crack closure. dc/dN-$\Delta$K$_{eff}$ relationships of short cracks are found to coincide well with the corresponding long crack relationships. accordingly. the growth rate of short cracks can be predicted using that of long cracks.ort cracks can be predicted using that of long cracks.cks.

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Self-healing and leakage performance of cracks in the wall of a reinforced concrete water tank

  • Gao, Lin;Wang, Mingzhen;Guo, Endong;Sun, Yazhen
    • Earthquakes and Structures
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    • v.16 no.6
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    • pp.727-741
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    • 2019
  • A reinforced concrete water tank is a typical functional liquid storage structure and cracks are the greatest threat to the liquid storage structure. Tanks are readily cracked due to seismic activity, thereby leading to the leakage of the stored liquid and a loss of function. In order to study the effect of cracks on liquid storage tanks, self-healing and leakage tests for bending cracks and through cracks in the walls of a reinforced concrete water tank were conducted. Material performance tests were also performed. The self-healing performance of bending cracks in a lentic environment and through cracks in a lotic environment were tested, thereby the self-healing width of bending micro-cracks in the lentic environment in the short term were determined. The through cracks had the capacity for self-healing in the lotic environment was found. The leakage characteristics of the bending cracks and through cracks were tested with the actual water head on the crack. The effects on liquid leakage of the width of bending cracks, the depth of the compression zone, and the acting head were determined. The relationships between the leakage rate and time with the height of the water head were analyzed. Based on the tests, the relationships between the crack characteristics and self-healing as well as the leakage were obtained. Thereby the references for water tank structure design and grading earthquake damage were provided.

A Study on the Prediction of Non-Propagating Behavior of Short Cracks (짧은 균열의 정류거동 예측에 관한 연구)

  • 한지원
    • Journal of the Korean Society of Safety
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    • v.9 no.1
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    • pp.161-164
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    • 1994
  • Computer aided unloading elastic compliance method was employed to measure the closure and the length of short cracks. The most significant factor that influences the fatigue growth behavior of short cracks is the crack closure Phenomenon. dc/dN-$\Delta$ $K_{eff}$ relationships of short cracks are found to coincide well with the corresponding long crack relationships. Non-propagating behavior of short cracks at notch root can be predicted from the crack opening SIF of short cracks, $K_{op}$ , and the growth equation of long cracks in Region I and II.n Region I and II.I.

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Extraction of Characteristics of Concrete Surface Cracks

  • Ahn, Sang-Ho
    • Journal of information and communication convergence engineering
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    • v.5 no.2
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    • pp.126-130
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    • 2007
  • This paper proposes a method that automatically extracts characteristics of cracks such as length, thickness and direction, etc., from a concrete surface image with image processing techniques. This paper, first, uses the closing morphologic operation to adjust the effect of light extending over the whole concrete surface image. After applying the high-pass filtering operation to sharpen boundaries of cracks, we classify intensity values of the image into 8 groups and remove intensity values belong to the highest frequency group among them for the removal of background. Then, we binarize the preprocessed image. The auxiliary lines used to measure cracks of concrete surface are removed from the binarized image with position information extracted by the histogram operation. Then, cracks broken by the removal of background are extended to reconstruct an original crack with the $5{\times}5$ masking operation. We remove unnecessary information by applying three types of noise removal operations successively and extracts areas of cracks from the binarized image. At last, the opening morphologic operation is applied to compensate extracted cracks and characteristics of cracks are measured on the compensated ones. Experiments using real images of concrete surface showed that the proposed method extracts cracks well and precisely measures characteristics of cracks.

Effect of process parameters on propagation of edge crack in the cold rolling (냉간 박판압연공정에서 공정변수가 엣지 크랙 성장에 미치는 영향)

  • Cui, Xiang Zi;Lee, S.H.;Lee, S.J.;Lee, J.B.;KIm, B.M.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.405-408
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    • 2009
  • Edge cracks in cold rolling always influence to the quality of productions, while the "V" shaped cracks were propagated by passing the roll gap. We set up the sizes and shapes of initial cracks in simulation according to the references from real productions. Different to in hot rolling, the cracks in cold rolling couldn't be reduced from propagation automatically after generated, even if these could be reduced by changing the process parameters. In this paper, we described the affections of process parameters on the propagation of edge cracks, such as reduction ratio and tension. We predicted that the dependence of the cracks propagations of changing of process conditions and expected to gain the smaller edge cracks. By raising the reduction ratio, the cracks were propagated increasingly in both transverse and rolling directions. And as tension raise, the cracks became propagated in both directions in which transverse direction was less effectively.

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A Study on the Interaction between Distributed Cracks (분포 크랙들 사이에서의 상호 간섭에 관한 연구)

  • Han, Moon-Sik;Cho, Ja-Eung
    • Transactions of the Korean Society of Automotive Engineers
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    • v.13 no.6
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    • pp.63-69
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    • 2005
  • For the case that center crack is surrounded by four small cracks which are symmetrically distributed around center crack, the same values of normalized stress intensity factor of center crack according to the position of the tip of small cracks are located on the smooth curve. And the stress intensity factor according to any position of small cracks can be sufficiently obtained from this curve. The plastic zones between distributed cracks are also investigated by changing the positions of nearly small cracks. The occurrence of plastic zone due to the interaction between center crack and small cracks are analyzed by finite element method. The mechanical behavior at the vicinity of crack tips is investigated by plastic areas. The changes of plastic zones according to positions of distributed cracks are drawn schematically. The safety of materials is also analyzed.

Characteristics of EMR emitted by coal and rock with prefabricated cracks under uniaxial compression

  • Song, Dazhao;You, Qiuju;Wang, Enyuan;Song, Xiaoyan;Li, Zhonghui;Qiu, Liming;Wang, Sida
    • Geomechanics and Engineering
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    • v.19 no.1
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    • pp.49-60
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    • 2019
  • Crack instability propagation during coal and rock mass failure is the main reason for electromagnetic radiation (EMR) generation. However, original cracks on coal and rock mass are hard to study, making it complex to reveal EMR laws and mechanisms. In this paper, we prefabricated cracks of different inclinations in coal and rock samples as the analogues of the native cracks, carried out uniaxial compression experiments using these coal and rock samples, explored, the effects of the prefabricated cracks on EMR laws, and verified these laws by measuring the surface potential signals. The results show that prefabricated cracks are the main factor leading to the failure of coal and rock samples. When the inclination between the prefabricated crack and axial stress is smaller, the wing cracks occur first from the two tips of the prefabricated crack and expand to shear cracks or coplanar secondary cracks whose advance directions are coplanar or nearly coplanar with the prefabricated crack's direction. The sample failure is mainly due to the composited tensile and shear destructions of the wing cracks. When the inclination becomes bigger, the wing cracks appear at the early stage, extend to the direction of the maximum principal stress, and eventually run through both ends of the sample, resulting in the sample's tensile failure. The effect of prefabricated cracks of different inclinations on electromagnetic (EM) signals is different. For samples with prefabricated cracks of smaller inclination, EMR is mainly generated due to the variable motion of free charges generated due to crushing, friction, and slippage between the crack walls. For samples with larger inclination, EMR is generated due to friction and slippage in between the crack walls as well as the charge separation caused by tensile extension at the cracks' tips before sample failure. These conclusions are further verified by the surface potential distribution during the loading process.

Automatic detection of tooth cracks in optical coherence tomography images

  • Kim, Jun-Min;Kang, Se-Ryong;Yi, Won-Jin
    • Journal of Periodontal and Implant Science
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    • v.47 no.1
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    • pp.41-50
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    • 2017
  • Purpose: The aims of the present study were to compare the image quality and visibility of tooth cracks between conventional methods and swept-source optical coherence tomography (SS-OCT) and to develop an automatic detection technique for tooth cracks by SS-OCT imaging. Methods: We evaluated SS-OCT with a near-infrared wavelength centered at 1,310 nm over a spectral bandwidth of 100 nm at a rate of 50 kHz as a new diagnostic tool for the detection of tooth cracks. The reliability of the SS-OCT images was verified by comparing the crack lines with those detected using conventional methods. After performing preprocessing of the obtained SS-OCT images to emphasize cracks, an algorithm was developed and verified to detect tooth cracks automatically. Results: The detection capability of SS-OCT was superior or comparable to that of trans-illumination, which did not discriminate among the cracks according to depth. Other conventional methods for the detection of tooth cracks did not sense initial cracks with a width of less than $100{\mu}m$. However, SS-OCT detected cracks of all sizes, ranging from craze lines to split teeth, and the crack lines were automatically detected in images using the Hough transform. Conclusions: We were able to distinguish structural cracks, craze lines, and split lines in tooth cracks using SS-OCT images, and to automatically detect the position of various cracks in the OCT images. Therefore, the detection capability of SS-OCT images provides a useful diagnostic tool for cracked tooth syndrome.

Influence of crack geometry on fatigue crack growth behavior in 5083- H113 aluminium alloy (5083-H113 A1 합금의 피로균열진전거동에 미치는 균열형태의 영향)

  • 김정규;신용승;윤의박
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.4
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    • pp.781-789
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    • 1988
  • The fatigue crack growth and crack closure behavior of long through-thickness cracks and small half-penny shaped surface cracks were investigated in 5083-H113 Aluminum alloy under constant amplitude testing by the unloading elastic compliance method. It was found that, in the Region II, the crack growth behavior of both through-thickness and surface cracks exhibited the tri-linear form with two transitions and no concern with stress ratio R. In the Region I $I_{ab}$ and I $I_{b}$, through-thickness cracks grew faster than surface cracks in length direction, but at .DELTA. K .leq.4 MPa.root.m for R=0.1 the growth rates of surface cracks in depth direction, grew faster than those of through-thickness cracks. When the crack closure was considered, the growth rates of through-thickness cracks lay between the growth rates of depth direction and the growth rates of length direction in surface cracks. It is suspected that this was caused by the difference of crack closure at depth and length direction of surface cracks.s.