• Korean Journal of Materials Research
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• v.12 no.8
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• pp.682-687
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• 2002

The three-dimensional estimation on the depth and height of flaw by using the difference of radiographic contrast density was studied. First, the specimens having artificial flaws of various depths and heights were prepared and the radiographic testing was performed. The radiographic depth of flaw was investigated and estimated on the effect of the scattered radiation with the change of distance between flaw and film. The height of flaw was estimated from the radiographic test with the reference specimen. The radiographic contrast with flaw depth decreased with increasing the flaw depth. The scattered radiation increased with increasing flaw depth and varied with the location between flaw and film. However, in the case of flaw height, the contrast density increased with increasing flaw height. It is thought due to the change in volume generating the scattered radiation which reaches a film.

• Journal of Welding and Joining
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• v.13 no.4
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• pp.132-146
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• 1995

Flaw classification(determination of the flaw type) and flaw sizing (prediction of the flaw shape, orientation and sizing parameters) are very important issues in ultrasonic nondestructive evaluation of weldments. In this work, new techniques for both classification and sizing of flaws in weldments are described together with extensive review of previous works on both topics. In the area of flaw classification, a methodology is developed which can solve classification problems using probabilistic neural networks, and in the area of flaw sizing, a time-of-flight equivalent(TOFE) sizing method is presented.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.604-609
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• 2003

Flaw geometries, applied stress, and material properties are major input variables for the fracture mechanics analysis. Probabilistic approach can be applied for the consideration of uncertainties within these input variables. But probabilistic analysis requires many assumptions due to the lack of initial flaw distributions data. In this study correlations are examined between initial flaw distributions and in-service flaw distributions on structures under cyclic load. For the analysis, LEFM theories and Monte Carlo simulation are applied. Result shows that in-service flaw distributions are determined by initial flaw distributions rather than fatigue crack growth rate. So initial flaw distribution can be derived from in-service flaw distributions.

• Journal of the Korean Society for Nondestructive Testing
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• v.2 no.1
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• pp.10-16
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• 1982

This study was carried out to measure the flaw height of welds in consideration of the effective probe angle in ultrasonic oblique detection. Specimens with inserted artificial flaws were made and flaw heights were estimated from detecting these specimens. Two different methods were applied to estimate flaw heights. From the result of the experiment, flaw height could be measured within the accuracy of 15% percent error and the difference between the probe distance method and beam path method is about 5% relatively small. It is considered that the results obtained this experimental study could be helpful informal ions for measuring flaw height.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.3-16
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• 1997

In modern high performance engineering applications, the structural integrity of materials and structures are quite often evaluated using fracture mechanics. This evaluation in turn requires information on the flaw geometry (location, type, shape, size, and orientation). The ultrasonic nondestructive evaluation (NDE) method is one technique that is commonly used to provide such information. Flaw classification (determination of the flaw type ) and flaw sizing (prediction of the flaw shape, orientation and sizing parameters) are very important issues for quantitative ultrasonic NDE. In this paper new approaches to both classification and sizing of flaws are described together with extensive review of previous works on both topics. In the area of flaw classification, a methodology is developed which can solve classification problems using probabilistic neural networks, and in the area of flaw sizing, a time-of-flight equivalent (TOFE) sizing method is presented. The techniques proposed here are in a form that can be used directly in many practical applications to quantitative estimates of the flaw's significance.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.9 no.1
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• pp.25-30
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• 2013

The periodic inspection of piping and pressure vessels welds in nuclear power plant has to provide reliable result related to weld flaws, such as location, maximum amplitude response, ultrasonic length, height and finally the nature or flaw pattern. The founded flaw in ultrasonic inspection is accepted or rejected based on these data. Specially, the amplitude of flaw response is used as basic parameter for flaw sizing and it may cause some deviation in length sizing result. Currently the ultrasonic inspections in nuclear power plant components are performed by specific inspection procedure which describing inspection technique include inspection system, calibration methodology and flaw characterizing. To perform ultrasonic inspection during in-service inspection, reference gain should be established before starting ultrasonic inspection by the requirement of ASME code. This reference gain used as basic criteria to evaluate flaw sizing. Sometimes, a little difference in establishing reference gain between calibration and field condition can lead to deviation in flaw sizing. Due to this difference, the inspection result may cause flaw sizing error. Therefore, the objective of this study is to compare and evaluate the ultrasonic amplitude difference between air filled and water filled pipe in nuclear power plant. Additionally, the accuracy of flaw sizing is estimated by comparing both conditions.

• 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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.1004-1010
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• 1992

In recent years, along with the development of ultrasonic probe with wide frequency range, the digitization of measuring instrument, and the development of operating process technics, it is possible to analyze ultrasonic pulse in frequency range. In this paper, applying to flaw model the ultrasonic spectroscopy method that can analyze ultrassonic pulse in frequency range, we examine the possibility of quantification of flaw and apply its result to the void and seperation in LSI package. Consequently, by using the change in frequency distribution and central frequency of sltrasonic pulse detected from flaw, the estimation of shape, size, and depth of flaw is possible. The change in central frequency is changed minutely by the sample materals and position of flaw, but changed mainly by the shape and size of flaw. And we can quantify the shape and size of flaw in LSI pakcage using the experimental result through flaw model.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.5 no.1
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• pp.14-19
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• 2009

NDE(Nondestructive examination) detects a flaw or discontinuity in materials. Flaws detected by the examination shall be evaluated for the decision basis of the integrity. The internal flaws of forging products can be detected by UT. However, UT has detection limits because of its reflected signal weakness. Normally, a 1mm or less flaw is known as the limit. If a flaw was detected, the size of flaw would be evaluated by AVG(or DGS) technique. To verify the evaluation data, alternative examination methods are needed. But there is no alternative examination methods until now. In this study, Phased array ultrasonic technique can be used to size the flaws in the generator rotor with focused beam of ultrasonic wave as a supplement method of AVG. Also, the phased array ultrasonic technique described enables the shape of flaw to be depicted exactly.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.05a
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• pp.197-198
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• 2016

The root cause of the crack flaw occurred in construction. This crack is represented by a construction flaw occurs in the concrete structure. Therefore, we introduce the basic properties for the type of concrete to crack reduction measures to minimize the causes flaw this paper.