• Journal of the Korean Society for Nondestructive Testing
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• v.16 no.1
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• pp.10-18
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• 1996

This study verified the relationship between fracture mechanics parameters and X-ray parameters for normalized SS41 steel with homogeneous crystal structure and M.E.F. dual phase steel(martensite encapsulated islands of ferrite). The fatigue crack propagation test were carried out and X-ray diffraction technique was applied to fatigue fractured surface. The change in X-ray parameters(residual stress, half-value breadth) according to the depth of fatigue fractured surface were investigated. The depth of maximum plastic zone, $w_y$, were determined on the basis of the distribution of the half-value breadth for normalized SS41 steel and that of the residual stress for M.E.F. dual phase steel. $K_{max}$ could be estimated by the measurement of $w_y$.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.115-123
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• 2007

For investigating self-diagnosis applicability, a method based on monitoring the changes in the electrical resistance of carbon fiber reinforced concrete has been tested. Then after examining change in the value of electrical resistance at each flexural weight-stage of carbon fiber in CFGFRP (carbon fiber and glass fiber reinforcing plastic) with new type rib and carbon sheet for concrete reinforcing, the correlations of electrical resistance and load as a function of strain, deflection were analyzed. As the results, it is clarified that when carbon fiber rod, rib and sheet fracture, the electrical resistance of it increase largely, and specially in case of CFGFRP, afterwards glass fiber tows can be resist the load due to the presence of the hybrid (carbon and glass) reinforced fiber. Therefore, it can be recognized that reinforcing bar and new type rib of CFGFRP and sheet of CF could be applied for self-diagnosis of fracture in reinforced FRP concrete.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.124-133
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• 2007

In our research, we focused on the FBG sensor system which is one of the fiber optic sensor system. The FBG sensor system is used for structural measurements. The problem of FBG sensor is very thin and weak. The methods that can protect FBG optical fiber sensor front outside forces such as the impacts are investigated. The FBG sensor embedded in the fiber reinforced composites which can replace the reinforcing steel bars in concretes can be applied to the concrete structures by embedding to the composite materials. The progresses in tensile strength of FBG sensor embedded in the reinforcing FRP bars in the concrete structures compare to plain FBGs were observed and the good long term durability is expected.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.157-163
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• 2007

Crack detection technique for concrete structures has been developed in this study. Experimental tests were carried out to detect a surface and internal crack, employing common fiber optic cables and OTDR(optical time domain reflectometry), an optical signal analyzer which is widely used to detect damages at fiber optic cables in the field of optical engineering. While initial concrete crack is ready to occur under cracking force, the occurrence and location of the crack are simultaneously detected to give the same damage to fiber optic cables which have been attached to and/or embedded into concrete in advance. It is obtained through successive tests that the principal factors for crack detection is the covering state of fiber optic cable, and total 4 tests including a preliminary test were conducted and the crack detection technique was verified. The practical usefulness would be expected at crack management and maintenance of concrete structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.173-182
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• 2007

Cracks in concrete structures should be measured to periodically assess potential problems in durability and serviceability. Conventional crack measurement systems depend on visual inspections and manual measurements of the crack features such as width, length, and direction using microscope and crack gage. However, conventional methods take long time as well as manpower, and lack quantitative objectivity resulted by inspectors. In this study, an evaluation technique for concrete surface cracks is developed using image processing and artificial neural network. Developed technique consists of three major parts: (1) crack detection (2) crack analysis and (3) pattern recognition. To examine validity of the technique developed in this study, crack analyzing tests were performed on the images obtained from various types of concrete surface cracks. The test results revealed that the system is highly effective in automatically analyzing concrete surface cracks in terms of features and patterns of cracks.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.5
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• pp.383-392
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• 2007

In this paper, we study the prediction of depth and width of a defect in steam generator tube in nuclear power plant using neural network. To this end, we first generate eddy current testing (ECT) signals for 4 defect patterns of SG tube: I-In type, I-Out type, V-In type, and V-Out type. In particular, we generate 400 ECT signals for various widths and depths for each defect type by the numerical analysis program based on finite element modeling. From those generated ECT signals, we extract new feature vectors for the prediction of defect size, which include the angle between the two points where the maximum impedance and half the maximum impedance are achieved. Using the extracted feature vector, multi-layer perceptron with one hidden layer is used to predict the size of defects. Through the computer simulation study, it is shown that the proposed method achieves decent prediction performance in terms of maximum error and mean absolute percentage error (MAPE).

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.5
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• pp.432-441
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• 2007

Image processing methods for an extraction of a nuclear fuel rod image and visualization methods of the RGB color data were studied with a sectional image of spent fuel assembly. The fuel rod images could be extracted by using a histogram analysis, an edge detection and RGB rotor data. In these results, a size of the spent fuel assembly could be measured by using a histogram analysis method and a shape of the spent fuel rod could be observed by using an edge detection method. Finally, a various analyses were established for status of the spent fuel assembly by realized various 3D images for the color data in an image of a spent fuel assembly.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.5
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• pp.393-397
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• 2007

Eddy current standard including an artificial slot for the calibration of absolute type surface probe was fabricated. Developed eddy current standard has the electric conductivity and dimensions, and contains artificial slot as established in ASTM E 1629. The width and depth of artificial slot are 0.1 mm and 0.5 mm respectively. This slot was only possible to measure the depth on the two side edges, and impossible for the middle part with general measurement tools. The ultrasonic test method was applied for measuring depth of the middle part of the artificial slot in the standard. Using this method the dimension could be measured successfully with uncertainty about $15\;{\mu}m$. Calibration of eddy current standard for the absolute probe can be performed by this technique.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.5
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• pp.449-458
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• 2007

In this paper, we reconstructed the cross-sectional images of two phantoms simulating a petrochemical process from gamma radiation measurements. Three different weight functions for EM image reconstruction algorithm were built and compared with histograms representing the variance of the homogeneity of the phantom material, The radiation source, $^{137}Cs$, collimated by a lead with 5 mm diameter aperture and the measurement was made with a lead shielded 1inch NaI detector. As a result, the method taking into account the beam area in each pixel for a weight function showed the best resolution among the three methods.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.336-342
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• 2006

Uniaxial stress in ail axisymmetric body is the simplest example of ultrasonic stress measurement. However, the birefringence theory cannot be applied for axisymmetric solids because the axisymmetric stress field in the body does not make shy velocity difference in SH waves propagating in the axisymmetric direction. Conventional ultrasonic technique using the time-of-flight method also needs ultrasonic lengths of the unstressed and stressed body, which is very impractical. In this paper, the birefringence effect in axisymmetric solids under uniaxial stress is formulated to evaluate the axial stress inside the solid without measuring tile ultrasonic length. Theoretical derivation for the birefringence characteristics in the axisymmetric solids is made using the longitudinal and shear waves instead of two horizontally polarized shear waves. Tension test is conducted for carbon-steel specimen to measure the birefringence coefficient and investigate the validity of the theory. It is observed from experimental results that the velocity difference in two differently polarized acoustic waves is proportional to the uniaxial stress in the axisymmetric solid with a good agreement with the theoretical value.