• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.2
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• pp.152-162
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• 2001

Laser-generated ultrasonic technique which is one of the reliable nondestructive evaluation techniques has been applied to evaluate the integrity of structures by analyzing the characteristics of signal obtained from surface crack. Therefore, the signal analysis of the laser-generated ultrasonics is absolutely necessary for the accurate and quantitative estimation of the surface defects. In this study, one-sided measurement by laser-generated ultrasonic has been applied to evaluate the depth of the surface-breaking crack in the materials. However, since the ultrasonic waveform excited by pulse laser is very difficult to distinguish the defect signals, it is necessary to consider the signal analyses of the transient waveform. Wavelet Transform(WT) is a powerful tool for processing transient signals with temporally varying spectra that helps to resolve high and low frequency transient components effectively. In this paper, the analyses of the surface-breaking crack of the ultrasonic signal excited by pulse laser are presented by employing the WT analyses.

• International Journal of Highway Engineering
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• v.3 no.4 s.10
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• pp.137-146
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• 2001

Pavement distresses are one of the most important data for pavement management systems. Inspection machines and its related programs have been used for operating tools in PMS developed in advanced countries. In Korea imported machines and programs for the length price ale utilized to get information of pavement condition from the field This study is launched for developing the program which can detect cracks on asphalt pavement due to many drawbacks in current PMS operation such as improper maintenance work and long resting period when it was broken. The focus of this study is to define principles to analyze pavement surface with digital image processing techniques, to test property of pavement images and to suggest an algorithm that reduces noises at test. To test images, the camera attached on the Automatic Road Analyser(ARAN) was used. Through the FFT images, histogram and statistical values of pavement images, it was found that the images had many noises with high-frequency components against general images, and it was difficult to subdivide pavement images into background or crack. Through several testing with various filters for noise reduction a 3X3 median filter was suggested to reduce noises effectively.

• The Journal of the Petrological Society of Korea
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• v.19 no.4
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• pp.283-292
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• 2010

The Suljeongri east three-story stone pagoda in Changnyeong (National Treasure No. 34) has been damaged mainly by lots of cracks. The stones used for this pagoda are medium-granied equigranular pinkish biotite granite. Measured magnetic susceptibility values are of from 2 to 9 (${\times}10^{-3}$ SI unit). From the ${\gamma}$-ray spectrometer mesurement K, eU, and eTh contents of the stones are 3 to 7%, 8 to 19 ppm, and 11 to 35 ppm, respectively. Comparing the petrographical and chemical characteristics between the stones of the pagoda and the country rocks near Suljeongri, it is suggested that the most similar rock could be equigranular biotite granite in the western slope of the Mt. Hwawangsan. Vertical, horizontal and diagonal cracks are intensely developed at the lower part of the stone pagoda. Biotite granite has intrinsic microcracks defined as rift and grain rock cleavages. Both rock cleavages are assumed to have led to the crack growth and consequent mechanical damage of the pagoda. It seems that vertical cracks have been grown parallel to the principal compressional stress, and that horizontal cracks to the reacting tensional stress. Diagonal cracks seems likely to have been resulted from conjugate rift and grain rock cleavages.

• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.589-597
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• 2010

Steel structures have a higher probability of being damaged by fatigue than by other causes of deterioration. As such, their maintenance to prevent fatigue damage is essential to sustain their safety and performance during their service period. In their maintenance, the current state of their fatigue cracks must be assessed to determine appropriate reinforcement methods and the suitable time intervals of periodic inspections when fatigue cracks are detected. Determining the crack growth rate is a successful method of predicting fractures, but it requires technical knowledge on fracture mechanics and experience in numerical methods and software for finite element analysis. In this study, a fatigue crack growth test on through-thickness cracked steel plates was conducted to assess the crack growth rate without superior technical knowledge and experience. The relationship between the Crack Opening Displacement (COD) and the crack growth rate was found in relatively long fatigue cracks.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.15-22
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• 2003

The fatigue crack growth model is derived and the retardation model is proposed. The fatigue crack growth model considers the residual plastic stretch on the crack surface which results from the plastic deformation at the tip of fatigue crack. The fatigue crack growth rate is calculated by using the cumulative fatigue damage and plastic strain energy in the material elements at the crack tip. This model gives the crack growth rate in reasonable agreement with test data for aluminum alloy AL6061-T651 and 17-4PH casting steel. The fatigue crack growth retardation model is based on the residual plastic stretch produced from a tensile overload which reduced the plastic strain range of the following load cycles. A strip-yield model of a crack tip plasticity is used for the calculation of a plastic zone size. The proposed retardation model characterized the observed features and delayed retardation of the fatigue crack growth under tensile overload.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.359-366
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• 2021

In this study, It was developed an monitoring cracks system based on image processing techniques in order to measure cracks, which are major damages in concrete, and to convert them into a database. The crack monitoring system consists of crack image captured equipment and a crack detection and analysis software. This system provides objective and quantitative data by replacing the conventional visual inspection. The crack detection algorithm w as verified through an indoor test using virtual cracks, and the amount of crack detection and crack width change was monitored by applying it to the self-healing repair mortar construction site. In the case of the crack width detected through image analysis, the maximum difference from the actual crack width was 0.0334mm. It was possible to detect microcracks of 0.1mm or less, and the effect of crack healing over time of the self-healing repair mortar was confirmed trough the field test.

• Magazine of the Korea Concrete Institute
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• v.7 no.3
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• pp.175-186
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• 1995

The determination of the stress intensity factors is investigated by sur-face integral method around the crack tip of the nlass~vc: concrete structure. The surface integral met hod is naturally derived from the standal-ci path integral J. Howevcr. In the J integral method, pressure in the crack-face and body forces can not be considered, while this theory has advantage of ccmsidering many kind of forces, so t.his theory will be useful in investigating more accurate strt:ss states around crack tip. Furthermore. t h~s rrlethod can elerninate unntussary process of using singular elements and fine mesh around crack tip which is used 11; modelling the singularity around crack tip. A computer program for determming $K_I$, $K_{II}$ is tfcvulopcd by applying this theory. $K_I$, $K_{II}$ values usmg X noded isoparametric elements which was proved and variation of the stress intensity factor was investigated by application of darn structures.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.391-396
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• 2004

Plastic shrinkage crack occurs at the exposed surfaces of freshly placed concrete due to consolidation of the concrete mass and rapid evaporation of water from the surface. This so-called shrinkage crack is a major concern for concrete, especially for flat structures such as pavements, slabs for industrial factories and retaining walls. This study has been performed to obtain the plastic shrinkage and the permeability of hydrophilic poly vinyl alcohol(PVA) fiber reinforced mortar and concrete. Test results indicated that PVA fiber reinforced cement composite showed an ability to reduce the total crack area and the maximum crack width (as compared to plain and polypropylene fiber reinforced concrete). Also, according to the permeability test result, it was found that PVA fiber reinforced cement composite was more reducing than polypropylene fiber reinforced cement composite.

• Journal of Conservation Science
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• v.27 no.3
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• pp.251-260
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• 2011

This study focus on the suggestion of standard legend, the process system on making method of deterioration map, the development of crack index (CI), and the evaluation techniques of surface and 3D deterioration rate for stone cultural heritage. The standard legends of deterioration forms were made using a common graphic program after crack, blistering, scaling, break-out, granular disintegration, and perforation were subdivided. The deterioration map improved accuracy and reliability on deterioration range using 3D digital restoration and high resolution photograph mapping technique. Also, quantitative deterioration evaluation of stone cultural heritage was carried out developing the crack index, and the 3D deterioration rate of a break-out part was calculated by virtual restoration modeling. As a quantitative deterioration evaluation of Magoksa Temple stone pagoda based on the results described above, the north face showed high deterioration rate of bursting crack (1.70), hair crack (1.34), scaling (20.2%) and break out (13.0%), and the 3D deterioration rate of first roof stone was 6.7%.

• Journal of the Korean Institute of Gas
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• v.27 no.3
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• pp.116-122
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• 2023

As the number of hydrogen filling stations for hydrogen supply increases with the progress of low-carbon eco-friendly energy policies, the risk of accidents is also increasing. Actual pressure vessels may have defects such as notches, pores, and inclusions that may occur during the manufacturing process. Therefore, it is necessary to evaluate the integrity of pressure vessels in the case where cracks exist in pressure vessels under internal pressure. In this paper, 3D finite element analysis was used to evaluate the structural safety of hydrogen-filled pressure vessels with surface cracks, and the shape of surface cracks was compared with the commonly used semi-elliptical shape. In the future, these results will be used to predict the remaining life of the pressure vessel in consideration of fracture mechanics.