• The Journal of Engineering Geology
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• v.28 no.3
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• pp.455-463
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• 2018

This study developed a method to quantitatively measure the size of cracks in concrete using X-ray CT images. We prepared samples with a diameter of 50 mm and a length of 100 mm by coring cracked concrete block that was obtained by chipping. We used a micro-focus X-ray CT, then applied the 3DMA method (3 Dimensional Medial axis Analysis) to the 3D CT images to find effective parameters for damage assessment. Finally, we quantitatively assessed the damage based on sample locations, using the damage assessment parameter. Results clearly show that the area near the chipping surface was damaged to a depth of 3 cm. Furthermore, X-ray methods can be used to evaluate the porosity index, burn number, and medial axis, which are used to estimate the damage to the area near the chipping surface.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.245-251
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• 2018

Recently, as the importance of structural maintenance has been increased, studies on self - healing concrete technology are being actively carried out. On the other hand, test for evaluating the self-healing performance is not standardized yet. Although visual test is used as a basic method for measuring crack widths, it is difficult to observe the crack width inside the specimen, and there is a disadvantage that only the local measurement of the surface can be measured due to the inhomogeneous cracking characteristics. Although permeability test has been widely used as an indirect method for measuring crack width, there is a problem due to the viscosity of water, and also a possibility that the internal material of the specimen may be eluted during the test. In this study, we propose a crack width evaluation method using gas diffusion characteristics. Idealized straight cracks were fabricated by acrylic and the diffusion coefficients of specimens were analyzed with respect to crack width and thickness. The experimental results show that the crack width and the diffusion coefficient are in a linear relationship and that the thickness and diffusion coefficient are inversely related.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.144-150
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• 2001

Considered is non-symmetric contact traction induced by the tilting of a contact body and/or by a far field bulk tensile load to the other body. The problem is under the regime of plane strain. General profile of the contact end is incorporated and partial slip condition is supposed. As an example contact configuration, an indentation of a punch with rounded corners onto a half plane is studied. The variation of the internal stress field due to the tilting and the bulk tension is investigated. An edge crack problem is analyzed to examine the influence of the non-symmetric traction. It is shown that the tilting of a punch does not influence the behaviour of the crack. Rather, the effect of the bulk tension on the cracking behaviour is found considerable.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.6
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• pp.455-463
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• 1998

RCCA(rod cluster control assembly) End-Tip suffers from neutron irradiation and constant vibration due to high-speed internal flow of primary coolant during plant operation. Such operating conditions cause the RCCA end-tip crackings around tile circumferential weldment of the end-tip, and in some cases, the defective end-tips were completly broken loose. However, no reliable inspection techniques for end-tip crackings were developed in the past, although some techniques exist for inspecting RCCA control rod wears. Therefore, NDE group at KEPRI has developed an ECT technique for the detection and the sizing of the end-tip crackings. The technique uses a specially designed surface-riding probe that can detect size of circumferential crackings with an accuracy of ${\pm}5.31%$ RMS error. This paper describes the ECT instrumentation including the ECT probes, calibration bars, as well as technical approaches.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.4
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• pp.443-449
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• 2012

Nanoskins were fabricated on a Ti-6Al-4V material by carrying out various surface treatments, i.e., deep rolling, laser shot peening, and ultrasonic nanocrystal surface modification (UNSM). These surface treatments are newly developed techniques and are becoming more popular for industrial applications. Fatigue tests were carried out using material test system (MTS); these tests included the axial loading tension-compression fatigue test (R = -1, RT, 5 Hz, sinusoidal wave) and rotating bending fatigue test (R = -1, RT, 3200 rpm). The analysis of the crack initiation pattern in the UNSM-treated material indicated that the crack was interior originating in the axial loading tension-compression cycle, and was surface originating in the bending fatigue test. UNSM treatment significantly improved the fatigue strength for the regime of above $10^6$ cycles that S-N curve of rotating bending stress clearly show the performance of a 5 mm titanium specimen after UNSM treatment is similar to that of an untreated 6 mm titanium specimen.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.32-38
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• 2001

Although the ultrasonic method has been developed and used widely in the fields, it has been used only for measuring the defect size and thickness loss. In this study, the relationship between surface wave attenuation through micro-crack growth and variation of velocity under repeated cyclic loading has been investigated. The specimens are adopted from 2.25Cr-1Mo steel, which is used for power plant and pipeline system, and have dimensions of $200{\times}40{\times}4mm$. The results of ultrasonic test with a 5MHz transducer show that surface wave velocity gradually decreases from the point of 60% of fatigue life and the crack length of 2mm with the increasing fatigue cycles. From the results of this study, it is found that the technique using the ultrasonic velocity change is one of very useful methods to evaluate the fatigue life nondestructively.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.10
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• pp.84-91
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• 2002

The shaft with the circular cross section have symmetric structural combination parts to keep the rotating balance. Hence the crack usually emanate from symmetric combination parts due to the stress concentration of these parts. In this study to estimate the fatigue behavior of symmetric cracks, the fatigue test was performed by using rotary bending tester and the specimen with symmetric defects in circular cross section. From the facts the characteristics of crack initiation and propagation on the symmetric surface cracks in circular cross section was examined. Also we observed the internal crack using oxidation coloring and investigated the fatigue behavior using the relationship between surface crack and internal crack. As a result of fatigue lift of symmetric cracks was reduced to 35% compared to single crack’s. We examined the characteristics of fatigue behavior in element with symmetric cracks using internal crack propagation rate and maximum stress intensity factor range obtained from approximation method.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.211-216
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• 2001

The components with the circular cross section have the symmetric combination parts for rotating balance and the crack emanates from the symmetric combination parts. The symmetric cracks from symmetric combination parts make a decrease in the component fatigue life more than single crack. In this study, to estimate the behavior of symmetric cracks, the fatigue test was performed using rotary bending tester on the specimen with a symmetric defects in circular cross section. The material used in this study is Ni-Cr-Mo steel alloy. Under the same stress, the result from the rotary bending fatigue test turned out that the symmetric cracks made a decrease in the fatigue life by 35% more than single crack and the relation between log a and cycle ratio $N/N_f$ obtained linearly.

• Journal of the East Asian Society of Dietary Life
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• v.26 no.3
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• pp.271-277
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• 2016

This study was performed to identify sensory characteristics of the Korean traditional cookie Yakgwa prepared by partially replacing wheat flour with glutinous rice flour as well as to conduct cross-cultural comparison of the sensory descriptions of the Yakgwa sample set between Korea and Chinese panelists. Korean and Chinese highly trained panelists identified 22 sensory attributes by descriptive analysis. The addition of glutinous rice flour decreased soybean oil odor, moistness, oiliness and increased hardness, crispness of the Yakgwa samples. In the consumer test, consumers from Korea (n=89) and China (n=56) participated. Yakgwa with 50% glutinous rice flour had a significantly higher overall acceptability than other the Yakgwa samples by Korean and Chinese consumers.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.1
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• pp.1-7
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• 1999

In order to determine the mode I stress intensity factor ($K_I$) by means of the alternating current potential drop(ACPD) technique, the change in potential drop due to load for a paramagnetic material containing a two-dimensional surface crack was examined. The cause of the change in potential drop and the effects of the magnetic flux and the demagnetization on the change in potential drop were clarified by using the measuring systems with and without removing the magnetic flux from the circumference of the specimen. The change in potential drop was linearly decreased with increasing the tensile load and was caused by the change in conductivity near the crack tip. The reason of decreasing the change in potential drop with increasing the tensile load was that the increase of the conductivity near the crack tip due to the tensile load caused the decreases of the resistance and internal inductance of the specimen The relationship between the change in potential drop and the change in $K_I$ was not affected by demagnetization and was independent of the crack length.