• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.4
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• pp.91-98
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• 2002

Prediction for the compressive strength of concrete by non-destructive tests(NDT) has a tendency to show different outcomes according to various aggregates. The purpose of this study is to develop estimation equation by rebound number, ultrasonic velocity and combined method at concrete structures which used granite as coarse aggregates. The test variable is water/cement ratio(41.1%, 48.6%, 67.6%), curing method(moisture condition, dry condition) and age(7, 14, 28, 56). According to the test variable, new equation was suggested, and compared with the existing equations.

• Journal of Mechanical Science and Technology
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• v.18 no.4
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• pp.640-648
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• 2004

This paper describes a new magnetization method for non-destructive testing with magneto-optical sensor (denoted as MO sensor) which have the following characteristic : high observation sensitivity, independence of the crack orientation, and precise imaging of a complex crack geometry such as multiple cracks. When a magnetic field is applied normally to the surface of a specimen which is significantly larger than its defects, approximately the same magnetic charge per unit area occurs on the surface of the specimen. If there is a crack in the specimen, magnetic charge per unit area has the same value at the bottom of the crack. The distribution of the vertical component of the magnetic flux density, B$\_$Z/, is almost uniform over the no-crack area (denoted as B$\_$Z,BASE/), while the magnetic flux density is smaller in the surroundings of the crack(denoted as B$\_$Z,CRACK/) If B$\_$Z, BASE/ is a bit larger than the saturated magnetic flux density of the MO sensor (B$\_$s/) , then small magnetic domains occur over the crack area and a large domain over the non-crack area because B$\_$Z,CRACK/ is smaller than B$\_$s/.

• Smart Structures and Systems
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• v.4 no.4
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• pp.391-406
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• 2008

This study attempts to develop a real-time debonding monitoring system for carbon fiber-reinforced polymer (CFRP) strengthened structures by continuously inspecting the bonding condition between the CFRP layer and the host structure. The uniqueness of this study is in developing a new concept and theoretical framework of nondestructive testing (NDT), in which debonding is detected without relying on previously-obtained baseline data. The proposed reference-free damage diagnosis is achieved based on the concept of time reversal acoustics (TRA). In TRA, an input signal at an excitation point can be reconstructed if the response signal measured at another point is reemitted to the original excitation point after being reversed in the time domain. Examining the deviation of the reconstructed signal from the known initial input signal allows instantaneous identification of damage without requiring a baseline signal representing the undamaged state for comparison. The concept of TRA has been extended to guided wave propagations within the CFRP-strengthened reinforced concrete (RC) beams to improve the detectibility of local debonding. Monotonic and fatigue load tests of large-scale CFRP-strengthened RC beams are conducted to demonstrate the potential of the proposed reference-free debonding monitoring system. Comparisons with an electro-mechanical impedance method and an inferred imaging technique are provided as well.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.241-245
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• 2006

In the examination of Steam Generator (SG) tube in Nuclear Power Plant (NPP) Eddy Current Testing (ECT) probes play an Important role in detecting the defects. Bobbin probe and Rotating Pancake Coil (RPC) probe is usually used for the inspection of SG tube. Bobbin probe is good at high speed inspection, but ability of detection of circumferential defect is very weak. On the contrary RPC probe, which moves for inspection in the direction of axial and circumferential simultaneously, has very slow inspection speed, but it was excellent detection capability fur small cracks, which is hardly detected by bobbin probe. Many examinations of SG tube examination of NPP are achieved during short period. Therefore, solution about this must develop probe of new form for examination performance and examination time shortening of other probe. In this paper, analyzed technological present condition of Bob-bin probe and RPC probe been using in Nondestructive Testing (NDT) for SG tube defect detection and Appeared about background theory and view of developed probe newly.

• Smart Structures and Systems
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• v.6 no.7
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• pp.851-866
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• 2010

This paper presents a new concept of using PZT (lead zircornate titanate) transducers as a non-destructive testing (NDT) tool for evaluating quality of concrete. Detection of defects in concrete is very important in order to check the integrity of concrete structures. The electro-mechanical impedance (EMI) response of PZT transducers bonded onto a concrete specimen can be used for evaluating local condition of the specimen. Measurements are carried out by electrically exciting the bonded PZT transducers at high frequency range and taking response measurements of the transducers. In this study, the compression test results showed that concrete specimens without sufficient compaction are likely to fall below the desired strength. In addition, the strength of concrete was greatly reduced as the voids in concrete were increased. It was found that the root mean square deviation (RMSD) values yielded between the EMI signatures for concrete specimens in dry and saturated states showed good agreement with the specimens' compressive strength and permeable voids. A quality metric was introduced for predicting the quality of concrete based on the dry-saturated state of concrete specimens. The simplicity of the method and the current development towards low cost and portable impedance measuring system, offer an advantage over other NDE methods for evaluating concrete quality.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.6 s.261
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• pp.718-724
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• 2007

Some of gas turbine model of 7F-Class has constructed and is operating with units domestically. Non-destructive testing (NDT) is one of the methods being used to inspect damage $1^{st}$ stage bucket and review damage trends. We also analyze damage configuration and microstructure according to material and compare with pape of electric power research institute (EPRI). The damaged mode could be determined by leveraging failure analysis. Especially, configuration uprate of bucket is not only to prevent damage during operation but also avoid domestic manufacturing by the competitors. Modifications were mainly concentrated on surfaces such as cooling hole and bucket tips. Analyzing of bucket damage, the earlier model of 7F-Class used with one cycle with equivalent operation hour (EOH), has various cracking of the bucket surface. Bucket damage of new model is centered on tip area (54%) as analyzed by EPRI research. We conclude that improving bucket configuration would increase repair rate on the bucket tip.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.1233-1240
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• 1996

Conventional measurement methods using ultrasonic wave or x-ray, eddy current for non-destructive testing(NDT) in nuclear power plants and other industrial plants have been utilized as the method of contact with objects to be inspected. For this reason these methods require relatively much time and inspection area is limited by the location of probe or film. But holograpic interferometry which is a non-contact optical measurement method using a coherent light source has an advantage that quantative measurement can be performed at a time. In this paper a new method using realtime holographic interfreometry and image processing for detecting internal flaws of pressure vessels is presented.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.6
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• pp.556-562
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• 2007

This paper presents the use of a novel fiber optic accelerometer system to monitor ambient vibration (both wind-induced one and vehicle-induced) of a real bridge structure. This sensor system integrates the $Moir\'{e}$ fringe phenomenon with fiber optics to achieve accurate and reliable measurements. A low-cost signal processing unit implements unique algorithms to further enhance the resolution and increase the dynamic bandwidth of the sensors. The fiber optic accelerometer has two major benefits in using this fiber optic accelerometer system for monitoring civil engineering structures. One is its immunity to electromagnetic (EM) interference making it suitable for difficult applications in such environments involving strong EM fields, electrical spark-induced explosion risks, and cabling problems, prohibiting the use of conventional electromagnetic accelerometers. The other is its ability to measure both low- and high-amplitude vibrations with a constantly high resolution without pre-setting a gain level, as usually required in a conventional accelerometer. The second benefit makes the sensor system particularly useful for real-time measurement of both ambient vibration (that is often used for structural health monitoring) and strong motion such as earthquake. Especially, the semi-strong motion and the small ambient one are successfully simulated and measured by using the new fiber optic accelerometer in the experiment of the structural health monitoring of a real bridge.

• Journal of the Korean Magnetics Society
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• v.21 no.1
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• pp.23-31
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• 2011

From among the NDT (nondestructive testing) methods, the MFL (magnetic flux leakage) method is specially suitable for testing pipelines because pipeline has high magnetic permeability. The system applied to MFL method is called the MFL PIG. The previous MFL PIG showed high performance in detecting the metal loss and corrosions. However, MFL PIG is highly unlikely to detect the cracks which occur by exterior-interior pressure difference in pipelines and the shape of crack is long and very narrow. In MFL PIG, the magnetic field is performed axially and there is no changes of cross-sectional area at cracks that the magnetic field passes through. Cracks occur frequently in the pipelines and the risk of the accident from the cracks is higher than that from the metal loss and corrosions. Therefore, the new PIG is needed to be researched and developed for detecting the cracks. The circumferential MFL (CMFL) PIG performs magnetic fields circumferentially and can maximize the magnetic flux leakage at the cracks. In this paper, CMFL PIG is designed and the distribution of the magnetic fields is analyzed by using 3 dimensional nonlinear finite element method (FEM). In CMFL PIG, cracks, standards of NACE, are detectable. To estimate the shape of crack, the leakage of magnetic fields for many kinds of cracks is analyzed and the method is developed by signal processing.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.1
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• pp.39-45
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• 2015

Applications of smart sensors have been extended to safety systems in the aerospace, transportation and civil engineering fields. In particular, structural health monitoring techniques using smart sensors have gradually become necessary and have been developed to prevent dangers to human life and damage to assets. Generally, smart sensors are based on electro-magnets and have several weaknesses, including electro-magnetic interference and distortion. Therefore, fiber optic sensors are an outstanding alternative to overcome the weaknesses of electro-magnetic sensors. However, they require expensive devices and complex systems. This paper proposes a new, affordable and simple sensor system that uses a single fiber to monitor pressures at multiple-points. Moreover, a prototype of the sensor system was manufactured and tested for a feasibility study. Based on the results of this experimental test, a relationship was carefully observed between the bend loss conditions and light-intensity. As a result, it was shown that impacts at multiple-points could be monitored.