• Journal of Mechanical Science and Technology
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• v.16 no.5
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• pp.591-598
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• 2002

Leakage magnetic flux is occurred in the cracked area of magnetized specimens, and also it changes the magnetic domain area of the magneto-optical film positioned on the specimen. It causes the change of the optical permeability of the magnetic domain on the crack area. So crack images can be obtained easily using this principle. On the other hand, utilizing a laser in this method makes possible to perform a remote sensing by detecting the light intensity contrast between cracked area and normal area. This paper shows the application of non-destructive inspection system taking advantage of magneto-optical method for micro-cracks and presents examples applied to the several types of specimens having fatigue cracks and fabricated cracks using this method. Also the authors prove the possibility of this method as a remote sensing system under the oscillation load considering application to real fields.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.252-253
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• 2019

Corrosion of rebars in reinforced concrete structures is a major factor that shortens the life of the structure. As corrosion progresses, the adhesion between the concrete tissues and the rebar decreases and the cracks in the concrete due to the expansion of the oxide intensify. Although it is necessary to measure corrosion behavior of rebars inside the concrete to measure degradation of structures due to rebar corrosion, no studies have been conducted to measure corrosion of rebars in In-situ state. In this study, corrosion of rebars in reinforced concrete specimens was attempted to be quantified using micro-computer tomography. Since corrosion of concrete takes several months per 10mm of cover, accelerated corrosion techniques were applied. Accelerated corrosion on the specimen was conducted by applying a 10 V magnetic field to the buried rebar and external electrodes with the specimen submerged in a 10% calcium chloride solution. The experiment found that within two weeks, more than 40% of rebar reduction occurred, and the cracks in the radial cracks occurred through the concrete structure, leading to the transfer of the oxide produced through the cracks to the surface of the specimen.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.6
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• pp.1388-1398
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• 1994

The fracture toughness and micro-fracture mechanisms of the porous glass and stainless fiber reinforced glass composite were evaluated by using the acoustice mission(AE) technique, fracture toughness $test(K_{IC})$ and the macroscopic observation of the specimen surface which was being under the loading. At initial portion of the loading, the AE signals with low energy, of which origins were considered as the micro-cracks formated at the crack tip, were emitted. With increasing the applied load, AE signals having higher energies were generated due to the coalesence of micro-cracks and fast fracture. Based on the such relationship between AE emission and loading condition, fracture toughness $K_{IAE}$ could be defined successfully be using the $K_I$ value corresponding to an abrupt change of the accumulated AE signal energies emitted during the fracture toughness test. In spite of its brittleness of glass material, nonlinear deformation behavior before maximum load was observed due to the formation of micro-cracks. Further, the stainless fiber may have attributed to the improvement of fracture toughness and the resistance to crack propagation comparing to noncomposited materials Finally, models of the micro-fracture process combined with the AE sources for the porous glass material and its composite were proposed paying attention to the micro-crack nucleation and its coalescence at the crack tip. Fiber fracture and its Pullout, deformation of fiber itself were also delinated from the model.

• Journal of the Semiconductor & Display Technology
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• v.12 no.3
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• pp.29-34
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• 2013

Solar cell has been considered as renewable green energy. Its silicon wafer thickness is thinner due to manufacturing cost and accordingly micro cracks is often generated in the process. Micro cracks result in bad quality of solar cell, and so their accurate and reliable detection is required. In this paper, near-infrared optics system is newly designed based on the analysis of near-infrared transmittance characteristics and its important parameters are optimally selected using the design of experiment for micro crack detection in solar cell wafer. The performance of the proposed method is verified using several experiments.

• Computers and Concrete
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• v.2 no.3
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• pp.189-202
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• 2005

This paper presents an analysis of some experimental results concerning micro-structural tests, permeability measurements and strain-stress tests of four types of High-Performance Concrete, exposed to elevated temperatures (up to $700^{\circ}C$). These experimental results, obtained within the "HITECO" research programme are discussed and interpreted in the context of a recently developed mathematical model of hygro-thermal behaviour and degradation of concrete at high temperature, which is briefly presented in the Part 2 paper (Gawin, et al. 2005). Correlations between concrete permeability and porosity micro-structure, as well as between damage and cracks' volume, are found. An approximate decomposition of the thermally induced material damage into two parts, a chemical one related to cement dehydration process, and a thermal one due to micro-cracks' development caused by thermal strains at micro- and meso-scale, is performed. Constitutive relationships describing influence of temperature and material damage upon its intrinsic permeability at high temperature for 4 types of HPC are deduced. In the Part II of this paper (Gawin, et al. 2005) effect of two different damage-permeability coupling formulations on the results of computer simulations concerning hygro-thermo-mechanical performance of concrete wall during standard fire, is numerically analysed.

• Tribology and Lubricants
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• v.11 no.5
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• pp.114-121
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• 1995

An ultrasonic technique using normal-incident compressional waves was used to evaluate the surface and subsurface damage in ceramics produced by Hertzian indentation. Damage was produced by a blunt indenter (tungsten carbide ball) in glass-ceramic, green glass and silicon nitride. The damage was classified into two types; (1) Hertzian cone crack, in green glass and fine grain silicon nitride, and (2) distributed subsurface micro fractures, without surface damage, produced in glass ceramic. The ultrasonic technique was successful in detecting cone craks. The measurement results with the Hertzian cone cracks indicated that cracks perpendicular to the surface could be detected by the normal-incident compressional waws. Also shown is the capability of normal-incident compressional waves in detection distributed micro-sized cracks size of subsurface microfractures.

• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05e
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• pp.85-88
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• 2003

In this study, porcelain insulator samples which have a different alumina composition were manufactured in order to test electrical and mechanical properties and make an analysis of the propagation phenomena of micro cracks on porcelain body. From XRD quantitative analysis the crystalline phases were different with alumina composition, sample C and D which have about 17wt% Corundum phase without the Cristobalite phase shows better electrical and mechanical properties than sample A and 8 which have the Cristobalite phase. In dielectrics test on porcelain samples with below 17wt% alumina composition, it was found that the amount of glass phase$(SiO_2)$have an main effect to decrease the dielectric loss$(tan{\delta})$, and the dielectric breakdown voltage of aluminous porcelain insulators was largely affected by its relative density. As a micro cracks analysis, HRS were measured, then the intensity of HRS increased with the amount of alumina composition. On the other hand, the propagation behaviors of cracks was fairly influenced by the distribution of pores.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.247-248
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• 2013

The waterproof construction for walls and floor in the underground parking lot in the construction of the apartment buildings have been excluded to the introduction of the waterproof design until now, because of the shorten construction period and the reduced construction costs. The concrete structures are existed to the joints in the vertical or horizontal parts commonly. In case of cracks, there are generated due to behavior by subsidence and external changing temperature environment. The cracks are generated by the frequent water leaks. So, the repair methods of the water leaks are proposed as the quick micro-cement and the polyacrylic resin in this study.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.9
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• pp.1746-1752
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• 2002

Fatigue fracture in machine components is produced by surface micro-crack from stress concentration area such as notch and material defect. It is difficult to predict the remaining fatigue lift of mechanical components because the surface micro-crack on critical area initiates and grows with statistical distribution. Plane bending fatigue tests were carried out on the plain specimen of Al 2024-T3 and the initiation and growth behavior of surface micro cracks were observed. The statistical distribution of surface length of multiple micro cracks and their maximum length were investigated. The maximum surface crack length distributions were analyzed on the basis of the statistics of extremes in order to examine the prediction of remaining life.