• Journal of the Korean Society of Safety
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• v.23 no.4
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• pp.7-12
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• 2008

This study proposes integrity evaluation method of weld zone in titanium using titanium distance amplitude characteristics curve(TDACC) and ultrasonic signals. For these purposes, the ultrasonic signals for porosity defects of weld zone in titanium are acquired in the type of time series data and echo strength. 4 lines in the DACC indicated damage evaluation standard of weld zone in titanium. The acquired ultrasonic signals agree fairly well with the measured results of reference block and sensitivity block(defect location, bean1 propagation distance, echo strength, etc). The proposed TDACC in this study agree fairy well with the measured results of weld zone in titanium(weld defects as porosity). The proposed TDACC in this study can be used for integrity evaluation of weld zone in titanium.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.6
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• pp.56-63
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• 2003

In this study, an automatic ultrasonic testing system is used to detect the defects of the natural flaw test specimen and of the artificial flaw test specimen. We evaluate the detection performance of the acceptance standard for the natural flaw test specimen and of the acceptance standard for the artificial flaw test specimen. We also study the potential problems of those acceptance standards. The results indicate that the acceptance standard for the detection of defects in weldzone is good then the sensitivity correction is performed and that we must clearly specify special check points of the acceptance standard for the system in use.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.6
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• pp.407-413
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• 2015

Ultrasonic infrared thermography is an active thermography methods. In this method, mechanical energy is introduced to a structure, it is converted into heat energy at the defects, and an infrared camera detects the heat for inspection. The heat generation mechanisms are dependent on many factors such as structure characteristics, defect type, excitation method and contact condition, which make it difficult to predict heat distribution in ultrasonic infrared thermography. In this paper, a method to simulate frictional heating, known to be one of the main heat generation mechanisms at the closed defects in metal structures, is proposed for ultrasonic infrared thermography. This method uses linear vibration analysis results without considering the contact boundary condition at the defect so that it is intuitive and simple to implement. Its advantages and disadvantages are also discussed. The simulation results show good agreement with the modal analysis and experiment result.

• Journal of applied mathematics & informatics
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• v.22 no.1_2
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• pp.193-208
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• 2006

A modified BFGS algorithm for solving the unconstrained optimization, whose Hessian matrix at the minimum point of the convex function is of rank defects, is presented in this paper. The main idea of the algorithm is first to add a modified term to the convex function for obtain an equivalent model, then simply the model to get the modified BFGS algorithm. The superlinear convergence property of the algorithm is proved in this paper. To compared with the Tensor algorithms presented by R. B. Schnabel (seing [4],[5]), this method is more efficient for solving singular unconstrained optimization in computing amount and complication.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.57-57
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• 2010

Sb(111) is a spin textured surface due to the strong spin-orbit coupling, often viewed as a proto-type topological insulator. We used scanning tunneling microscopy (STM) to characterize various Mn-induced subsurface defects existing at the surface of Mn-doped Sb at 50 K. Our STM images show that every defect exhibits 3-fold symmetry with a single rotational orientation and can be categorized by their shapes and sizes. We found more than 10 types of subsurface defects with distinctive orders, which allows the resolution of the vertical positions of the magnetic dopants lying more than 10 layers down from the surface. We will discuss about our findings in comparison with theoretical results.

• Transactions of Materials Processing
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• v.16 no.3 s.93
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• pp.178-186
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• 2007

Rheo-forging process of aluminum alloy is suitable for large parts of net shape without defects and excellent mechanical properties in comparison with conventional die casting and forging process. To control the microstructure of the product with high mechanical properties in rheo-forming, solid fraction is required to prevent porosity and liquid segregation. Therefore, in rheo-forging process, die shape, pressure type and solid fraction are very important parameters. The defects such as porosity, liquid segregation and unfitting phenomena occur during rheo-forging process. To prevent these defects, mechanical properties and microstructure analysis of samples versus the change of pressure are carried out and the problem and its solutions are proposed. Also, the mechanical properties versus various pressures were compared with and without heat treatment. The alloys used for rheo-forming are A356 and 2024 aluminum alloy. The rheology material is fabricated by electromagnetic process with controlling current and stirring time.

• Proceedings of the KIEE Conference
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• 2001.04a
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• pp.102-104
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• 2001

This paper presents a numerical analysis of the eddy current testing for pipe with axi-symmetric defect according to frequency changes using the finite element method(FEM). The defects used in this analysis are inner and outer axi-symmetric type. In order to obtain the behaviors of the signals by changing the frequency, the defects with different depths are modeled and analyzed using FEM. It is important to choose proper frequency because of the effect of skin depth in eddy current testing. This paper describes signal characteristics of each defects as frequency is changed.

• Journal of Electrical Engineering and information Science
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• v.3 no.2
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• pp.170-173
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• 1998

In practice, there may be various defects in an insulating system, so that the PD signals can be produced from these defects simultaneously. Regarding these situations, we have to discriminate the type of defect as well as determine whether the PD occurs or not. In this paper, some analysis results of the PD signals from multi-defects insulating system were presented. We measure the PD signals by using three kind of electrode system, IEC(b), Needle-Plane and mixed electrodes. To simulate multi-defect systems, we combined to electrode systems and apply test voltage simultaneously. Neural network, statistical analysis methods were tried, and the possibilities and limitations of each method were clarified.

• Journal of Chest Surgery
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• v.21 no.4
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• pp.757-760
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• 1988

Double mitral valve orifice is an unusual congenital abnormality, and is rarely of clinical importance. That abnormality not produce hemodynamic deficits, but it has been associated with other congenital heart diseases, especially atrioventricular canal defects, and so it is surgically important condition. After the first report by M.S. Greenfield in 1876, there are only a few reported cases all over the world. We experienced two cases of double mitral valve orifice with atrioventricular canal defect. The small accessory mitral orifice was placed in anterior mitral leaflet as a hole type in both cases. The A-V canal defects are corrected with a one patch technique, but the accessory orifices are left unclosed because there were no mitral regurgitations through the orifice. On the 4th postoperative day, the patients have been performed echocardiography; both had no mitral regurgitation. Both of patients are now being follow-up and we find no specific problems. A small accessory mitral orifice may be left unclosed and rarely produce significant regurgitation, conclusively.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.69-70
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• 2022

In this study, although the diversity of tiles in the expanding housing market is increasing, cases of defects in building interior tiles that occur due to limitations of existing tile adhesives and construction methods were collected, and among them, the relationship between the coefficient of thermal expansion and the occurrence of defects was analyzed. One-way ANOVA was used for the analysis method, and as a result of the analysis, it was analyzed that the difference between groups in temperature difference and humidity difference by defect type was significant.