• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.306-311
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• 2003

A growing fatigue crack is known to be retarded on application of an overload cycle. The retardation may be characterized by the total number of cycles involved during retardation and the retarded crack length. The overload ratio plays an important role to influence the retardation behavior. The objective of the present investigation is to study the effect of different overload ratio on the retardation behavior. For DENT(double edge notched tension) specimens and ESET(eccentrically-loaded single edge crack tension) specimens, fatigue crack growth tests are conducted under cyclic constant-amplitude loading including a single tensile overloading with different overload ratios. The proposed crack retardation model predicts crack growth retardation due to a single tensile overloading. The predictions are put into comparison with the experimental results to confirm the reliability of this model.

• 대한기계학회논문집A
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• 제24권1호
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• pp.103-109
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• 2000

A method to measure the crack length in rubbery materials is described. Through dimensional analysis and experiments, an equation is derived to give the crack length as a function of the change of strain energy density in a region remote from the crack. The function is provided in a form of separated terms of loading and material, the validity of which is experimentally proved using separation parameters.

• Structural Engineering and Mechanics
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• 제3권6호
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• pp.541-553
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• 1995

The determination of the stress intensity factors is investigated by using the surface integral defined around the crack tip of the structure. In this work, the integral method is derived naturally from the standard path integral J. But the use of the surface integral is also extended to the case where body forces act. Computer program for obtaining the stress intensity factors $K_I$ and $K_{II}$ is developed, which prepares input variables from the result of the conventional finite element analysis. This paper provides a parabolic smooth curve function. By the use of the function and conventional element meshes in which the aspect ratio (element length at the crack tip/crack length) is about 25 percent, relatively accurate $K_I$ and K_{II}$ values can be obtained for the outer integral radius ranging from 1/3 to 1 of the crack length and for inner one zero.

• 한국정밀공학회지
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• 제18권5호
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• pp.34-41
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• 2001

More accurate and fast inspection method for mechanical parts and structure is required to guarantee the safety. Conventional methods using compliance method, eddy current method, ultrasonic wave, acoustic emission for non-destructive testing in mechanical parts and structure have been performed as the method of contact with objects to be inspected. With this reason these methods have been taken relatively much time, money, and manpower. In this study, in order to overcome these shortcomings, we used In-plane Electronic Speckle pattern Interferometry(In-plane ESPI) that was full-field measurement and noncontact method. We detected the cracks of the specimen at a real time and measured the length of the crack by using In-place ESPI system. Finally, we compared this results with conventional microscope method.

• 한국소음진동공학회논문집
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• 제19권12호
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• pp.1281-1288
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• 2009

Variation of dynamic characteristics of a low pressure turbine blade with crack length is studied in this paper via both experiments and finite element model. Since most of the turbine blades used in domestic power plants are imported from abroad, it is necessary to understand their dynamic behavior in advance. When experimentally obtained natural frequencies and mode shapes are compared with those from FEM results, they are close to each other in their magnitude. Then, it is more feasible to use finite element model for analyzing the dynamic characteristics of a blade under various operation conditions (rotation speed, temperature, etc) as well as with a crack in the blade.

• The Korean Journal of Ceramics
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• 제5권2호
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• pp.119-124
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• 1999

Silicon nitride ceramics with highly oriented microstructure were prepared by tape casting a slurry containing 5 wt% of the silicon nitride whiskers. The whiskers were aligned in the casting direction and worked as seeds for the grain growth. The anisotropy was observed from the sintering shrinkage, Vickers indentation crack lengths, and XRD patterns. The cracks were much longer on the surface normal to the aligned grains than on the tape casting surface where the lateral cracks were also observed. The effect of sintering additives and the annealing treatment on the indentation crack length was examined. The sample with higher silica content had longer cracks than the one with lower silica content. The crack length anisotropy increased after annealing at 2123K.

• 동력기계공학회지
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• 제16권1호
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• pp.72-77
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• 2012

Acoustic emission (AE) is known to be sensitive to fracture process and so it was expected that AE data may propose as a means of monitoring the fracture information. The aim of this study is to analyze the characteristic of AE signal emitted from glass during Vickers indentation. To observe AE characteristics by surface effect, both glass and coating glass were studied. During Vickers indentation loading, AE signal resulted from penny-like crack is detected. During Vickers indentation unloading, AE signal resulted from both radial/median crack and lateral crack is detected. In case of indentation on glass, the emission energy(${\epsilon}$) is found to be approximately proportional to the fourth power of the crack length. In case of indentation on coating glass, the emission energy(${\epsilon}$) is approximately proportional to the crack length.

• 한국자동차공학회논문집
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• 제7권7호
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• pp.214-220
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• 1999

In order to use effectively a machinery part with fillet, it is necessary to determine a proper fillet shape in design step, Study of such problem by fracture mechanical criterion is rare. So, this paper focuses on the design of fillet radius in fracture mechanical aspect. Finite element method was used to obtain crack tip stress intensity factor. Stress intensity factor was calculated by COD(crack opening displacement0method proposed by Ingraffea and Manu. The parameter used in this study are thickness ration, filet radium and crack length . If fillet radius increase , crack propagation may be accelerated. Critical crack length is inversely proportional to fillet radius.

• Journal of Advanced Marine Engineering and Technology
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• 제22권4호
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• pp.522-528
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• 1998

This paper presents a fundamental fractal characteristics of the growing crack that has an irregularity producing a zigzag crack contour. This irregularity is analysed by a fractal geometry in a box counting method that is a very simple technique. First the fractal dimensions and actual fractal extensive crack length are obtained. Also a fractal fracture energy relation with a fractal dimension is found so as to get fractal crack behaviors. Thus it can be shown that the fractal dimension has a possibility as a fracture parameter in a real crack growth length meaning.

• Computers and Concrete
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• 제21권6호
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• pp.727-739
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• 2018

Crack is the most common typical feature of concrete deterioration, so routine monitoring and health assessment become essential for identifying failures and to set up an appropriate rehabilitation strategy in order to extend the service life of concrete structures. At present, image segmentation algorithms have been applied to crack analysis based on inspection images of concrete structures. The results of crack segmentation offering crack information, including length, width, and area is helpful to assist inspectors in surface inspection of concrete structures. This study proposed an algorithm of image segmentation enhancement, named morphological segmentation based on edge detection-II (MSED-II), to concrete crack segmentation. Several concrete pavement and building surfaces were imaged as the study materials. In addition, morphological operations followed by cross-curvature evaluation (CCE), an image segmentation technique of linear patterns, were also tested to evaluate their performance in concrete crack segmentation. The result indicates that MSED-II compared to CCE can lead to better quality of concrete crack segmentation. The least area, length, and width measurement errors of the concrete cracks are 5.68%, 0.23%, and 0.00%, respectively, that proves MSED-II effective for automatic measurement of concrete cracks.