• Imaging Science in Dentistry
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• v.35 no.3
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• pp.167-173
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• 2005

Purpose : To investigate the relationship between three-dimensional (3D) bone imaging parameters and trabecular strength in the mandible. Materials and Methods : Bone specimens were obtained from the mandibles of five male pigs weighing around 110 kg each. Of those, 43 samples were selected for 3D analysis and measured by micro-computed tomography. The five morphometric parameters were trabecular thickness (Tb.Th), bone specific surface (BS/BV), percent bone volume (BV/TV), structure model index (SMI) and degree of anisotropy (DA). Through destructive mechanical testing, strength parameters were obtained. Results : BV/TV, SMI, BS/BV, and Tb.Th showed significant correlations with strength parameters. DA did not show any correlation with the other parameters. In multiple linear regression analysis, BV/TV alone explained $43\%$ of the variance in Young's modulus. By stepwise inclusion of SMI, the variance in the Young's modulus was better explained up to $52\%$. Conclusions : Predicting trabecular strength in the mandible through architectural analysis would be possible. Further study is needed to establish the tendency and variety of trabecular architecture and strength according to the locations within the mandible.

• Journal of Conservation Science
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• v.30 no.4
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• pp.467-480
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• 2014

This study was focused on measurement methods for stone cultural heritages by analyzing Ultrasonic (P-wave) velocity variations according to the water content and anisotropy of rocks. As a result of analyzing of rock properties, the water content and saturation degree were rapidly changed at the beginning of drying and then showed exponential curve which their rates of change gradually decreased. However, P-wave velocity and its rate of change maintained constant values after natural drying of 10 hours. Therefore, the ultrasonic measurement for stone cultural heritages should be performed after natural drying of 10 hours considering the weather and moisture conditions. In addition, the highest values of anisotropy coefficient exhibited in granite and limestone, and indirect method was insensitive to anisotropy compared to direct method. However, all rocks remained anisotropy by indirect method. Accordingly, ultrasonic measurement considering various directions is required. The research results will contribute to customized non-destructive testing and precise diagnosis for lithological characteristics of stone cultural heritage.

• IEIE Transactions on Smart Processing and Computing
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• v.6 no.1
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• pp.66-70
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• 2017

Radioactive materials are used in medicine, non-destructive testing, and nuclear plants. Source localization is especially important during nuclear decommissioning and decontamination because the actual location of the radioactive source within nuclear waste is often unknown. The coded-aperture imaging technique started with space exploration and moved into X-ray and gamma ray imaging, which have imaging process characteristics similar to each other. In this study, we simulated $21{\times}21$ and $37{\times}37$ coded aperture collimators based on a modified uniformly redundant array (MURA) pattern to make a gamma imaging system that can localize a gamma-ray source. We designed a $21{\times}21$ coded aperture collimator that matches our gamma imaging detector and did feasibility experiments with the coded aperture imaging system. We evaluated the performance of each collimator, from 2 mm to 10 mm thicknesses (at 2 mm intervals) using root mean square error (RMSE) and sensitivity in a simulation. In experimental results, the full width half maximum (FWHM) of the point source was $5.09^{\circ}$ at the center and $4.82^{\circ}$ at the location of the source was $9^{\circ}$. We will continue to improve the decoding algorithm and optimize the collimator for high-energy gamma rays emitted from a nuclear power plant.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.300-312
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• 1993

The material deterioration of service-exposed boiler tube steels in fossil power plant was evaluated by using the electrochemical technique namely, modified electrochemical potentiokinetic reactivation(EPR). It was focused that the passivation of Mo$_{6}$C carbide which governs the mechanical properties of Mo alloyed steels did not occur even in the passivity region of steel in sodium molybdate solution and the reactivation peak current (Ip) observed as the result of non-passivation indicating the precipitation of Mo$_{6}$C carbides. To obtain the optimal test conditions for the field test by using the specially designed electrochemical cell, the effects of scan rate, the surface roughness and the pH of electrolyte on Ip value were also investigated. Furthermore, the change of mechanical properties occurred during the long time exposure at high temperature was evlauated quantitatively by small punch(SP) tests and micro hardness test taking account of the metallurgical changes. It is known that reactivation peak current (Ip) has a good relationship with Larson-Miller Parameter(LMP) which represents the information about material deterioration occurred at high temperature environment. In addition it was possible to estimate the ductile-brittle transition temperature (DBTT) by means of the SP test. The Sp test could be, therefore, suggested as a reliable test method for evaluating the material degradation of boiler tube steels. From the good correaltion between the SP DBTT and Ip values shown in this study, it was knows that the change of mechanical properties could be evaluated non-destructively by measurring only Ip values.ues.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.2
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• pp.67-78
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• 1990

An inverse self-iterative procedure is developed to determine layer moduli which are significant for the structural evaluation of pavements in developing rational and analytical rehabilitation technique. Falling weight deflectometer(FWD) is adopted as a non-destructive testing(NDT)device. The layer elastic theory is used to interpret NDT data. The theoretical deflection basins of pavement structures obtained by full factorial design are used for a parametric study on the characteristics of deflection basins and regression analyses. Regression equations to estimate layer moduli of flexible pavements are proposed through the regression analyses of theoretical deflection basins. The relationships between the rate of change of moduli and deflections are developed for the efficient iteration. An inverse self-iterative procedure to ensure the accuracy of the layer moduli is proposed. Validity and applicability of the developed procedure are verified through various numerical model tests.

• Smart Structures and Systems
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• v.10 no.3
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• pp.229-251
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• 2012

Guided waves have shown a great potential for structural health monitoring (SHM) applications. In contrast to traditional non-destructive testing (NDT) methodologies, a key element of SHM approaches is the high process of automation. The monitoring system should decide autonomously whether the host structure is intact or not. A basic requirement for the realization of such a system is that the sensors are permanently installed on the host structure. Thus, baseline measurements become available that can be used for diagnostic purposes, i.e., damage detection, localization, etc. This paper contributes to guided wave-based inspection in anisotropic materials for SHM purposes. Therefore, computational strategies are described for both, the solution of the complex equations for wave propagation analysis in composite materials based on exact elasticity theory and the popular global matrix method, as well as the underlying equations of two active damage localization algorithms for anisotropic structures. The result of the global matrix method is an angular and frequency dependent wave velocity characteristic that is used subsequently in the localization procedures. Numerical simulations and experimental investigations through time-delay measurements are carried out in order to validate the proposed theoretical model. An exemplary case study including the calculation of dispersion curves and damage localization is conducted on an exemplary unidirectional composite structure where the ultrasonic signals processed in the localization step are simulated with the spectral element method. The proposed study demonstrates the capabilities of the proposed algorithms for accurate damage localization in anisotropic structures.

• Computers and Concrete
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• v.22 no.1
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• pp.101-116
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• 2018

As one of the most important engineering structures, arch dams are huge constructions built with human hands and have strategical importance. Because of the fact that long construction duration, water supply, financial reasons, major loss of life and material since failure etc., the design of arch dams is very important problem and should be done by expert engineers to determine the structural behavior more accurately. Finite element analyses and non-destructive experimental measurements can be used to investigate the structural response, but there are some difficulties such as spending a long time while modelling, analysis and in-situ testing. Therefore, it is more useful to conduct the research on the laboratory conditions and to transform the obtained results into real constructions. Within the scope of this study, it is aimed to determine the structural behavior of arch dams considering experimentally validated prototype laboratory model using similitude and scaling laws. Type-1 arch dam, which is one of five arch dam types suggested at the "Arch Dams" Symposium in England in 1968 is selected as reference prototype model. The dam is built considering dam-reservoir-foundation interaction and ambient vibration tests are performed to validate the finite element results such as dynamic characteristics, displacements, principal stresses and strains. These results are considered as reference parameters and used to determine the real arch dam response with different scales factors such as 335, 400, 416.67 and 450. These values are selected by considering previously examined dam projects. Arch heights are calculated as 201 m, 240 m, 250 m and 270 m, respectively. The structural response is investigated between the model and prototype by using similarity requirements, field equations, scaling laws etc. To validate these results, finite element models are enlarged in the same scales and analyses are repeated to obtain the dynamic characteristics, displacements, principal stresses and strains. At the end of the study, it is seen that there is a good agreement between all results obtained by similarity requirements with scaling laws and enlarged finite element models.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10b
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• pp.74-78
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• 1992

This paper describes an intelligent system to automatic evaluation of eddy current(EC) signal for Inspection of steam generator(SG) tubes in nuclear power plant. Some features of the intelligent system design in the proposed system are : (1) separation of representation scheme ,or event capturing knowledge in EC signal and for structural inspection knowledge in SG tubes inspection; (2) each representation scheme is implemented in different methods, one is syntactic pattern grammar and the other is rule based production. This intelligent system also includes an data base system and an user interface system to support integration of the hybrid knowledge processing methods. The intelligent system based on the proposed concept is useful in simplifying the knowledge elicitation process of the rule based production system, and in increasing the performance in real time signal inspection application.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.181-186
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• 2006

An imaging method of seismic sources using time-reversal wave propagation is presented. The method is based on the time-reversal invariance and the spatial reciprocity of the wave equation. Time-reversal wave propagation has been used to image anomalous features of a midium in medical imaging, non destructive testing and waveform tomography. Seismogram is the record whose energy is propagated from the seismic source. If time-reversed seismogram propagates back into the medium, seismic energy is concentrated at the origin time of the event and at the source location. In this work, a staggered-grid finite-difference method of the elastic wave equation is parallelized for 3-D wave propagation simulation. With numerical experiments, we show that the time-reversal imaging will enable us to explore the spatio-temporal history of complex earthquake.

• Tunnel and Underground Space
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• v.27 no.5
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• pp.333-342
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• 2017

In this study, the heterogeneity of internal structure of various igneous rocks acquired in Korea was quantified and correlated with the seismic velocity and the point load strength. Three-dimensional X-ray Computed Tomography (CT) was used to obtain information on the internal structure of the rock specimen, and the representative unit length (LR) was calculated by applying a statistical technique to the CT images. We also proposed an estimation equation to predict the mechanical properties of rocks from the relationship between LR, acoustic velocity and point load strength. In the proposed method, it is shown that the characterization of internal structure of rocks could be utilized as an indirect index to account for the mechanical behavior of rocks by substituting physical laboratory testing for non-destructive test.