• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.4 no.2
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• pp.46-49
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• 2008

NDE(Nondestructive examination) detects a flaw or discontinuity in materials. Flaws detected by the pre-service or in-service examinations shall be sized for the purpose of analysis and repair. A flaw that is initiated from the surface is difficult to determine its depth by NDE. The depth of the surface flaw can be measured using an ultrasonic diffracted wave. To find the optimum standard for ultrasonic parameter(For example, frequency & size of transducer), a mock-up test and simulation were established and studied. This inspection technology may show the depth sizing possibility of the flaw down to nearly two(2) mm.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.4
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• pp.155-160
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• 2001

KS-code(KS B 0896) for nondestructive ultrasonic testing classifies the quality level by relative flaw size only. But flaw position is more important than the flaw size. Test blocks having artificial holes near surface show lower yield load than the blocks having deeply located holes from the surface. So, level calibration table was proposed for classifying the quality level of welded steel structures.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.386-389
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• 1999

Effect of high voltage screening was examined on mechanical strength of titania ceramics with two different surface roughness. Roughly finished sample showed degraded mechanical strength meaning that the introduced flaw played the role of starting point of mechanical fracture. On such sample, electrically weak parts were eliminated by applying a screening field. Mechanical strength measurement on survived parts revealed that after screening the Weibull plots bended to become a convex curve while plots at high strength region were almost the same. This result means that relatively low mechanical strength parts were eliminated by the electrical method. As a result the Weibull modulus calculated from all the data increased, demonstrating the effect of high voltage screening on titania ceramics containing fracture controlling surface flaws. Roles of the surface flaw such as a common weak spot for both failures are disscussed in relation to the electric field concentration similar to that of mechanical stress.

• 연구논문집
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• s.32
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• pp.55-64
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• 2002

Performance demonstration with real flawed specimens has been strongly required for nondestructive evaluation of safety class components in nuclear power plant. Specimen has been designed to produce mechanical fatigue flaw with tension stress and fatigue flaw has been produced to control stress and cycle, for suitable roughness. Notch condition is considered for control of fracture mode. After seal welding for fracture surface, final welding was performed to complete flaw specimen with GTAW(Gas Tungsten Arc welding) and FCAW(Flux Cored Arc Welding). It was demonstrated flaw size of flawed specimen by radiographic. testing and ultrasonic testing.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.658-662
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• 2001

The classification of surface flaw types was performed on the basis of angular dependence of backscattered ultrasound. The copper line adhered on the surface, cower line filled in groove, pure groove and the normal edge were adopted as various surface flaw patterns of glass specimen. A backward longitudinal profile was formed probably by the longitudinal wane scattering at and near 1st critical angle. The wave trains at the peak angles of the backward radiation profiles showed different shapes according to the superposition ratio of scattered and leaky waves. The asymmetry of the backward radiation profile arose due to the scattering effect of flaw. The additive resonance effect of copper line appeared in the left side of the profile. The peak angles of both the longitudinal and radiation profiles were shifted toward small angle by the scattering effect.

• Journal of the Korean Institute of Intelligent Systems
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• v.10 no.2
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• pp.75-82
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• 2000

This paper presents a method of detecting surface flaw of cold-rolled steel plate using image processing technique and a neural network classifier. The amount of steel plate surface image data is reduced by the wavelet transform. Features are extracted from the co-occurence matrix of the partial image corresponding to the low-frequency region, and a MLP neural network classifies into predetermined surface flaw categories. Simulations show the neural network classifier outperforms conventional vector quantization method.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1729-1734
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• 2016

The surface inspection of a steel billet is a common practice in the steel manufacturing process prior to hot rolling to produce steel wire for tire cord. This billet surface inspection is an important process because flaws on the surface may cause major failures during the product manufacturing phase. This paper presents a computer simulation based on a finite element method for a magnetic flaw detector with a function of the current intensity, the number of coil turns, and the billet proceeding speed during the production phase based on the typical condition of conventional apparatus. Based on the simulation result, the magnitude of the electromagnetic field on the surface diminished with distance from the electromagnet. In addition, the increased current intensity and the increased number of coil turns actually induced a stronger electromagnetic field on the billet surface. On the other hand, the proceeding speed of a billet in its production line had no significant effects. The result in this study may assist to reduce trial and error and to minimize the opportunity costs during the optimization process by applying the findings of this study into the operation condition in the steel billet production line.

• Journal of the Korean Society for Nondestructive Testing
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• v.12 no.2
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• pp.7-13
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• 1992

In this study, we examine the characteristics of beam and the effect of these characteristics on the flaw detection by using different type of two transducers, which are PZT and PVDF film transducer. Consequently, the detection of infinitesimal flaw is more possible than PZT, since it has beam width at focus of $60%{\sim}65%$ in contrast with PZT's. Moreover we can know PVDF transducer has superiority in detecting ability for sub-surface flaw detection in view of its acoustic impedance is near to water's and its focusing range is narrower than PZT's as $65{\sim}85%$ because it has spherical surface.

• Journal of the Korean Society of Safety
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• v.15 no.2
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• pp.46-50
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• 2000

A theoretical model for the evaluation of small surface fatigue crack initiated from a pit-type surface flaw is presented. The low frequency scattering model is developed based on the reciprocity principle for the elastic wave scattering. The effect of the flaw on the surface wave reflection from the crack is taken into account approximately by means of the stress intensity factor of cracks on a through thickness hole. The reflection coefficient of surface wave is derived for the prediction of small surface crack depth. Calculated results for pits with different sizes are illustrated.

• Journal of the Korean Society for Nondestructive Testing
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• v.7 no.1
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• pp.42-50
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• 1987

Most of significant defects in the pressure boundaries of nuclear power plant we re dispositioned to be monitored periodically every inservice inspection. Due to the difficulty of the defect sizing during operation, it is necessary to develope the continuous flaw monitoring techniques. The Tip Diffraction method, specifically speaking, spot seems to be suitable for flaw monitoring. The optimum conditions of selecting the transducer were 3.5 MHz and 45-57 degree according to compatibility with the defect height. The effective calculation of the defect height was to assume the fact that the incident beam is parallel. This method would be supplemented to ASME method about the defect characterization for the surface flaw.