• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.481-484
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• 2004

A form of measured temperature distribution to estimate condition of a electrical apparatus is a absolute reference for condition of the apparatus, time rate of transition, and difference between reference and currently temperature. Because passive thermography which has not injection of external thermal stimulation shows difference of temperature being on surface of a structure and temperature difference between the structure and back ground, the result could apply only to estimation or monitor for condition of terminal relaxation and overload related with temperature rising. However, a thermal flow in active thermography is differently generated by structure and condition of surface and subsurface. This paper presents the nondestructive testing using the properties and includes the results by heat injection and cooling to the apparatus. The buried discontinuity of subsurface could be detected by these techniques.

• Journal of Welding and Joining
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• v.1 no.2
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• pp.69-75
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• 1983

Both in-process quality control and reliability of the weld is one of the major concerns is applying friction welding. No reliable nondestructive monitoring method is available at present to determine the weld quality particularly in process of production. So that, this paper presents an experimental examination and quantitative analysis for the effects of initial acoustic emission(AE) counts on the weld strength relating to the rotating speed as a new approach which attempts finally to develop an on-line quality monitoring system design for friction welds using AE techniques. As one of the important results, it was well confirmed that the initial AE counts occurring during plastic deformation period of welding were quantitatively correlated with reliability at 95% confidence level to the joint strength of welds, tube-to-tube (SM 20 C to STS 304) and then an AE technique using the initial AE counts can be reliably applied to in-process strength monitoring of the weld.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.185-191
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• 2001

The aluminum die-casting technique has been widely used to manufacture a rotor in motor industry because of its highly productivity, even though it sometime causes the various type of defects in the rotor, such as shrinkage, cavity, blow holes etc. which results in the decrease of the efficiency of system. Therefore the development of reliable technique to detect the flaws in the rotor is strongly needed not only to control quality assurance but to improve its efficiency. In this study, the wide variety of ultrasonic techniques have been applied to detect the flaws in the rotor and then to discuss the detectibility of the flaw and the applicability for NDE tool in the aluminum die-casting rotor.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.391-398
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• 2016

Acoustic emission (AE) is one of the most powerful techniques for detecting damages and identify damage location during operations. However, in case of the source location technique, there is some limitation in conventional AE technology, because it strongly depends on wave speed in the corresponding structures having heterogeneous composite materials. A compressed natural gas(CNG) pressure vessel is usually made of carbon fiber composite outside of vessel for the purpose of strengthening. In this type of composite material, locating impact damage sources exactly using conventional time arrival method is difficult. To overcome this limitation, this study applied the previously developed Contour D/B map technique to four types of CNG storage tanks to identify the source location of damages caused by external shock. The results of the identification of the source location for different types were compared.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.2
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• pp.31-39
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• 1993

It has not been performed to inspect the underclad cracking of nuclear pressure vessel in Korea since there is no code requirements for inspection. However, underclad cracks in nuclear pressure vessels have been reported since the early 1970s. The aim of this experiment is to find the suitable ultrasonic inspection techniques for underclad cracking. The various transducers, for example $70_{\backprime}$ refracted longitudinal wave, 50/70 multibeam, SLIC-40, SLIC-50, are used in this investigation. Experiments on prescreening blocks and a demonstration block under the same condition as in the nuclear power pressure vessels show that the $70_{\backprime}$ refracted longitudinal wave method is the best one for the length evaluation and also gives a good signal pattern for detection of the crack, while the 50/70 multibeam transducer is more effective for the detection of underclad cracking. On the other hand, the SLIC-50 transducer using M-SPOT(Satellite Pulse Observation Technique) and M-PET (Peak-Echo Technique) methods is the most effective one for the depth of underclad crack estimation.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.4
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• pp.304-310
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• 2005

The techniques in order to measure the depth of defect in weldment and structure accurately have been developed. Many researches have made efforts to develop the methods for the accurate depth sizing of defect. TOFD is known as the most accurate method of various methods for measuring depth sizing. However, there is a possibility to miss defects because of the limitation of beam coverage for the ultrasound incident angle. In this study, the results for detectability and depth sizing using phased array ultrasonic technique for thick body were compared with those of conventional TOFD technique. It was experimentally confirmed that the phased array ultrasonic TOFD technique gives good detectability and accurate depth measurement for the various types of defects. The phased array ultrasonic TOFD technique developed in this study will contribute to increase the inspection reliability in thick component such as the pressure vessel of power generation industry.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.2
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• pp.186-196
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• 2004

In each country, the periodic ISI(In-Service Inspection) is required by the law to protect the public health and property from the potential accident of the nuclear facilities. To support the implementation of ISI program, the prescriptive ISI technical standards have been established. As the key parts of the ISI program, the non-destructive examination techniques are widely used to identify the degree of degradation of the pressure boundary components and welds. Recently, the risk informed-ISI program has been developed and implemented in several countries. Nonetheless, the existing ISI program which prescriptively decides the scope of inspection still has its own significance. In this article, the technical standards of ISI in leading countries like US, france, Canada, and Japan are reviewed and compared with the safety guide by IAEA. An outline to revise the domestic technical standards of ISI has been suggested.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.458-465
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• 2009

In general, ultrasonic guided wave techniques that used for an evaluation of the internal defect have been applied without considering energy loss. It can be found out that the significant attenuation is observed in the signal of structure with defect by the scattering and absorption. Even in the signal acquired from defect-free structure, this attenuation can be also significant. Therefore, it is very essential to determine the Lamb wave propagation characteristics depending on modes because the dispersibility of Lamb wave can be easily influenced by the attenuation effect with frequency and thickness. For this reason, changing the propagation distance, attenuation coefficient of each Lamb wave mode needs to be investigated by the contact pitch-catch method with PZT(piezoelectric) sensors. In this paper, the experimental attenuation coefficient is measured by choosing the following three different variables; mode, thickness and plate materials. As a result, experimental attenuation coefficient is obtained as the function of variables.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.149-154
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• 2012

The size and distribution of welding residual stress and welding deformation in welding structures have an effect on various sorts of damage like brittle failure, fatigue failure and stress corrosion cracking. So, research for this problem is necessary continuously. In this study, non-destructive technique using laser electronic speckle pattern interferometry, plate of welding specimen according to the external load on the entire behavior of residual stress are presented measurement techniques. Once, welding specimen force tensile loading, using electronic speckle pattern interferometry is measured. welding specimen of base metal and weld zone measure strain from measured result, this using measure elastic modulus. In this study, electronic speckle pattern interferometry use weld zone and base metal parts of the strain differences using were presented in residual stress calculated value, This residual stress value were calculated by numerical calculation. Consequently, weld zone of modulus high approximately 3.7 fold beside base metal and this measured approximately 8.46 MPa.

• 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.