• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.146-147
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• 2021

In this study, the deterioration of concrete subjected to high temperature was evaluated using harmonics. When concrete is exposed to high temperatures, its mechanical properties deteriorate. In order to evaluate this deterioration, a method of analyzing the waveform of elastic waves was applied. As the heating temperature increased, the fundamental wave of the 50 kHz elastic wave passing through the concrete decreased. In addition, harmonics were generated at each temperature, and the higher the heating temperature, the greater the ratio of harmonics. The higher the compressive strength, the greater the amplitude of the fundamental wave, and this phenomenon is thought to be due to the internal structure of concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.183-184
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• 2022

In this study, harmonics of 100 kHz ultrasonic pulse transmitted through concrete exposed to high temperature were evaluated. Concrete exposed to high temperatures deteriorates its mechanical properties. In ultrasonic pulse, the fundamental wave was attenuated by the deterioration of the concrete. In addition, it was possible to confirm the occurrence of harmonics. It is thought that the fundamental and harmonics of ultrasonic pulse greatly affected by the internal structure of concrete.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.300-312
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• 1993

The material deterioration of service-exposed boiler tube steels in fossil power plant was evaluated by using the electrochemical technique namely, modified electrochemical potentiokinetic reactivation(EPR). It was focused that the passivation of Mo$_{6}$C carbide which governs the mechanical properties of Mo alloyed steels did not occur even in the passivity region of steel in sodium molybdate solution and the reactivation peak current (Ip) observed as the result of non-passivation indicating the precipitation of Mo$_{6}$C carbides. To obtain the optimal test conditions for the field test by using the specially designed electrochemical cell, the effects of scan rate, the surface roughness and the pH of electrolyte on Ip value were also investigated. Furthermore, the change of mechanical properties occurred during the long time exposure at high temperature was evlauated quantitatively by small punch(SP) tests and micro hardness test taking account of the metallurgical changes. It is known that reactivation peak current (Ip) has a good relationship with Larson-Miller Parameter(LMP) which represents the information about material deterioration occurred at high temperature environment. In addition it was possible to estimate the ductile-brittle transition temperature (DBTT) by means of the SP test. The Sp test could be, therefore, suggested as a reliable test method for evaluating the material degradation of boiler tube steels. From the good correaltion between the SP DBTT and Ip values shown in this study, it was knows that the change of mechanical properties could be evaluated non-destructively by measurring only Ip values.ues.

• Structural Engineering and Mechanics
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• v.26 no.5
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• pp.499-516
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• 2007

An experimental method denoted as Impulse Method is proposed as a cost-effective non-destructive technique for the on-site evaluation of concrete elastic modulus in existing structures: on the basis of Hertz's quasi-static theory of elastic impact and with the aid of a simple portable testing equipment, it makes it possible to collect series of local measurements of the elastic modulus in an easy way and in a very short time. A Hypothesis Testing procedure is developed in order to provide a statistical tool for processing the data collected by means of the Impulse Method and assessing the possible occurrence of significant variations in the elastic modulus without exceeding some prescribed error probabilities. It is based on a particular formulation of the renowned sequential probability ratio test and reveals to be optimal with respect to the error probabilities and the required number of observations, thus further improving the time-effectiveness of the Impulse Method. The results of an experimental investigation on different types of plain concrete prove the validity of the Impulse Method in estimating the unknown value of the elastic modulus and attest the effectiveness of the proposed Hypothesis Testing procedure in identifying significant variations in the elastic modulus.

• Smart Structures and Systems
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• v.13 no.6
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• pp.1041-1063
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• 2014

This work introduces a two-module robotic pipe inspection system with ultrasonic NDE device to evaluate the integrity of pipe structures. The proposed robotic platform has high mobility. The two module mobile robot platform overcomes pipe obstacle structures such as elbow, or T-branch joints by cooperative maneuvers. Also, it can climb up the straight pipeline at a fast speed due to the wheel driven mechanism. For inspection of pipe structure, SH-waves generated by EMAT are applied with additional signal processing methods. A wavelet transform is implemented to extract a meaningful and specific signal from the superposed SH-wave signals. Intensity ratio which is normalized the defect signals intensity by the maximum intensity of directly transmitted signals in the wavelet transforms spectrum is applied to evaluate defects quantitatively. It is experimentally verified that the robotic ultrasonic inspection system with EMAT is capable of non-destructive inspection and evaluation of defects in pipe structure successfully by applying signal processing method based on wavelet transform.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.35-36
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• 2006

In Nd:YAG laser welding, evaluation methods of welding flaw are various. But, the method due to fume shape is difficult to classification of welding flaw. The Nd:YAG laser process is known to have high speed and deep penetration capability to become one of the most advanced welding technologies. At the present time, some methods are studied for measurement of fume shape by using high-speed camera and photo diode. This paper describes the machining characteristics of SM45C carbon steel welding by use of an Nd:YAG laser. In spite of its good mechanical characteristics, SM45C carbon steel has a high carbon contents and suffers a limitation in the industrial application due to the poor welding properties. In this study, fume shape was measured by infrared thermal camera that is non-contact/non-destructive thermal measurement equipment through change of laser generating power, speed, focus. Weld was performed on bead-on method. Measurement results are compared as two equipments. Here, two results are composed of measurement results of fume quantities due to fume shape by infrared thermal camera and inspection results of weld bead include weld flaws by ultrasonic inspector.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.957-965
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• 2011

Recently, railway industry has been developed not only functional parts such as acceleration and high performance of the railway but also emotional parts such as improved ride comfort and blocking noise. However, some important components of railway such as wheel and rail always had exposed too much operation time, cyclic load and rolling contact directly. The variations of load, vibration and chemical compositions were caused of wheel and rail having a lot of different types of contact fatigue damages. Therefore, It is necessary to improve inspection and maintenance technology in order to ensure safety and reliability of railway. Many researchers have already been reported the technology. Magnetic camera, one of the non-destructive testing technique can be used to inspect and evaluate the changes of magnetic field in ferromagnetic and paramagnetic materials with cracks. When an electromagnetic is applied to a specimen, a magnetic field will be distorted around a crack on the specimen. In present paper, the distribution of magnetic property in wheel with cracks using magnetic camera had investigated. The crack can be detected and evaluated by distribution analysis of magnetic field. The magnetic camera technique can be detected and evaluated the crack by rolling contact fatigue.

• Journal of Welding and Joining
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• v.18 no.1
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• pp.46-51
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• 2000

Ultrasonic nondestructive evaluation (UNDE) technique is commonly used for detecting inner defects in the materials. Recently, new methods are trying to apply for detecting surface and subsurface flaws using Rayleigh wave or creeping wave. These techniques, however, have following problems. Echo amplitude is remarkably affected by the surface conditions and discrimination of echo pattern is usually difficult because shear wave propagate in the material at the same time. We can apply surface SH-wave(which is horizontally polarized shear wave traveling along near surface layer) technique to detect surface flaws. In this paper, directivity, distance amplitude characteristics and detectability of surface flaws at fillet weld hills of the 5 MHz and 2 MHz surface flaws at fillet weld hills of the 5 MHz and 2 MHz surface Sh-wave are experimentally investigated. As a result of the study, it was found out that these techniques are valuable for the detection of fatigue cracks at fillet weld heels which can not be detected by other ultrasonic techniques such as angle beam technique and which are inaccessible for non-destructive testings e.g. MT(magnetic particle testing) or PT(liquid penetrant testing).

• Journal of the Korean Society of Safety
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• v.33 no.2
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• pp.152-157
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• 2018

The degradation and damage of the components for ballasted track could be caused a serious problem for railway safety. Therefore, the integrity evaluation of ballasted track condition is important to ensure and predict that the track safety and track maintenance. Various track components such as rail pad, ballast, sleeper, and rail that are widely used in Republic of Korea and represent a range of physical properties have been selected for this research. In this study, the experimental modal analysis was performed by the non-destructive testing. Modal test results were obtained from the field test and used to assess the condition of the track components. From the field test, the system of ballasted track was found to be simplified as a two-degree-of-freedom(2DOF) dynamic system. The condition of track component was found to directly affect the dynamic response of ballasted tracks. As the results, the dynamic properties of the track component was depend on the track condition and was distributed more roughly and over a wider range than its initial design values. Further, the methodology presented in this study is possible to determine experimentally the fundamental track parameters which are required in the numerical analysis, and also are useful for the safety assessment of track condition.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.4
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• pp.398-413
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• 2011

For railway safety, it is very important to detect damages of rails at their early stage because any undetected damage in a rail can break the rail and cause a serious railway accident. In this paper, several NDT applicable to rail inspections are described. Major damage types in rails are discussed first and the rail inspection technology using conventional piezoelectric ultrasonic transducers, which is widely adopted for damage detection of rails, is explained. Other NDT being researched or tested for rail inspection are also discussed as complementary technologies to the concurrent contact type ultrasonic inspection. Characteristics of each rail inspection technologies are evaluated in order to provide requirements for future development of a new rail inspection method.