• Korean Journal of Materials Research
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• v.9 no.12
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• pp.1240-1244
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• 1999

In order to assess the effects on the magnetic properties due to the defect in the material irradiated by fast neutron ranging $10^0-10^{18}n/cm^2$, the magnetic properties such as maximum magnetic induction, coercivity, remanence, Barkhausen Noise Amplitude(BNA), Barkhausen Noise Energy(BNE) and hardness were measured. It is shown that the magnetic properties and hardness do not change by the fast neutron irradiation under $10^{17}n/cm^2$. Therefore, in this experiment, it is understood that the magnetic properties decrease by the increase of hardness. This measurement method can be used to evaluate the neutron irradiation embrittlement nondestructively since the magnetic properties and hardness do change by the neutron irradiation over $10^{17}n/cm^2$ consistently.

• Journal of Food Hygiene and Safety
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• v.21 no.4
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• pp.204-212
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• 2006

This study was conducted to investigate the possibility of rapid and non-des tructive evalution of AV (Acid Value), IV (Iodine Value) and fatty acids in sesame oils. The samples were scanned over the range $400\sim2500nm$ using transmittance spectrum of NIRS(Near-infrared spectroscopy). A calibration equation calculated by MPLS regression technique was developed and correlation coefficient of determination for AV, IV, palmitic acid, stearic acid, linoleic acid and linolenic acid content were 0.9907, 0.9677, 0.9527, 0.9210, 0.9829, 0.9736 and 0.9709 respectively. The validation model for measuring the AV content had R of 0.989, SEP of 0.058 and IV content had R of 0.944, SEP of 0.562 and palmitic acid content had R of 0.924, SEP of 0.194 and stearic acid content had R of 0.717, SEP of 0.168 and oleic acid content had R of 0.989, SEP of 0.221 and linoleic acid content had R of 0.967, SEP of 0.297 and linolenic acid content had R of 0.853, SEP of 0.480 by MPLS. The obtained results indicate that the NIRS procedure can potentially be used as a non-destructive analysis method for the purpose of rapid and simple measurement of AV, IV and fatty acids in sesame oils.

• Journal of Conservation Science
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• v.37 no.5
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• pp.451-463
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• 2021

In this study we conducted component analyses of portable XRF detectors using four Au-Cu alloy standard samples to improve their accuracy by drawing up a calibration curve based on ICP-OES standard values. The portable XRF analysis found absolute errors of 0.3 to 3.7 wt% for Au and 0.2 to 8.2 wt% for Cu, confirming that the error range and standard deviation differed from one detector to another. Furthermore, the calibration curve improved their accuracy, such that the relative error rates of Au and Cu decreased from 9.8% and 14% to 3.5% and 3.7%, respectively. Accordingly, an experiment to confirm the calibration curve was conducted using unknown samples, finding that the measured values of the unknown samples fell on the calibration curve. Therefore, to accurately analyze the components of metal cultural heritage items, it is necessary to prepare a calibration curve for each element after checking whether the detector is suitable for the artifact.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.37 no.3
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• pp.167-175
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• 2019

Water color analysis allows non-destructive estimation of abundance of optically active water constituents in the water body. Recently, there have been increasing needs for light-weighted multispectral cameras that can be integrated with low altitude unmanned platforms such as drones, autonomous vehicles, and heli-kites, for the water color analysis by spectroradiometers. This study performs the preprocessing of the Micasense Rededge-M camera which recently receives a growing attention from the earth observation community for its handiness and applicability for local environment monitoring, and investigates the applicability of Rededge-M data for water color analysis. The Vignette correction and the band alignment were conducted for the radiometric image data from Rededge-M, and the sky, water, and solar radiation essential for the water color analysis, and the resultant remote sensing reflectance were validated with an independent hyperspectral instrument, TriOS RAMSES. The experiment shows that Rededge-M generally satisfies the basic performance criteria for water color analysis, although noticeable differences are observed in the blue (475 nm) and the near-infrared (840 nm) band compared with RAMSES.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.92-95
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• 2019

In this paper, a novel laser-based non-contact and non-destructive stress measurement technique is newly proposed for measuring stress in steel structural members. As the demand of stress monitoring in structural members is increased, various non-destructive techniques are being applied to the field of structural health monitoring. Spectroscopic techniques are non-contact technique and widely used for chemical identification of target materials. Especially, piezospectroscopic technique is a residual stress measurement technique in thermal barrier coatings. Although the piezospectroscopic technique has high possibility of measuring structural stress in steel members, the technique has been rarely applied to this field. In this paper, piezospectroscopy-based stress measurement technique is, therefore, proposed for measuring stress in steel structural member. To do that, alumina particles have been coated onto a specimen of a structural steel rod using a thermal spray coating technique. And then, an uniaxial compression test has been conducted to the specimen to collect each fluorescence spectrum under different loading conditions. Finally, the linear relation of spectral shift and applied compressive stress of the specimen has been experimentally established.

• Explosives and Blasting
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• v.37 no.3
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• pp.13-24
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• 2019

This paper was prepared to investigate the behavior of fragments in underwater torpedo explosion beneath a frigate or surface ship by using an explicit finite element analysis. In this study, a fluid-structure interaction (FSI) methodology, called the multi-material arbitrary Lagrangian-Eulerian (MM-ALE) approach in LS-DYNA, was employed to obtain the responses of the torpedo fragments and frigate hull to the explosion. The Euler models for the analysis were comprised of air, water, and explosive, while the Lagrange models consisted of the fragment and the hull. The focus of this modeling was to examine whether a worst-case fragment could penetrate the frigate hull located close (4.5 m) to the exploding torpedo. The simulation was performed in two separate steps. At first, with the assumption that the expanding skin of the torpedo had been torn apart by consuming 30% of the explosive energy, the initial velocity of the worst-case fragment was sought based on a well-known experimental result concerning the fragment velocity in underwater bomb explosion. Then, the terminal velocity of the worst-case fragment that is expected to occur before the fragment hit the frigate hull was sought in the second step. Under the given conditions, the possible initial velocities of the worst-case fragment were found to be very fast (400 and 1000 m/s). But, the velocity difference between the fragment and the hull was merely 4 m/s at the instant of collision. This result was likely to be due to both the tremendous drag force exerted by the water and the non-failure condition given to the frigate hull. Anyway, at least under the given conditions, it is thought that the worst-case fragment seldom penetrate the frigate hull because there is no significant velocity difference between them.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.400-414
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• 2021

Under high-level radioactive waste repository conditions, bentonite as an engineered barrier material undergoes thermal, hydrological, mechanical, and chemical processes. We report the applications of X-ray Computed Tomography (CT) imaging technique on the characterization and analysis of bentonite over the past decade to provide a reference of the utilization of this technique and the recent research trends. This overview of the X-ray CT technique applications includes the characterization of the bentonite either in pellets or powder form. X-ray imaging has provided a means to extract grain information at the microscale and identify crack networks responsible for the pellets' heterogeneity. Regarding samples of pellets-powder mixtures under hydration, X-ray CT allowed the identification and monitoring of heterogeneous zones throughout the test. Some results showed how zones with pellets only swell faster compared to others composed of pellets and powder. Moreover, the behavior of fissures between grains and bentonite matrix was observed to change under drying and hydrating conditions, tending to close during the former and open during the latter. The development of specializing software has allowed obtaining strain fields from a sequence of images. In more recent works, X-ray CT technique has served to estimate the dry density, water content, and particle displacement at different testing times. Also, when temperature was added to the hydration process of a sample, CT technology offered a way to observe localized and global density changes over time.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.4
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• pp.341-353
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• 2022

Pipelines are buried in urban area, and the position (depth and orientation) of buried pipeline should be clearly identified before ground excavation. Although various geophysical methods can be used to detect the buried pipeline, it is not easy to identify the exact information of pipeline due to heterogeneous ground condition. Among various non-destructive geo-exploration methods, ground penetration radar (GPR) can explore the ground subsurface rapidly with relatively low cost compared to other exploration methods. However, the exploration data obtained from GPR requires considerable experiences because interpretation is not intuitive. Recently, researches on automated detection technology for GPR data using deep learning have been conducted. However, the lack of GPR data which is essential for training makes it difficult to build up the reliable detection model. To overcome this problem, we conducted a preliminary study to improve the performance of the detection model using finite difference time domain (FDTD)-based numerical analysis. Firstly, numerical analysis was performed with homogeneous soil media having single permittivity. In case of heterogeneous ground, numerical analysis was performed considering the ground heterogeneity using fractal technique. Secondly, deep learning was carried out using convolutional neural network. Detection Model-A is trained with data set obtained from homogeneous ground. And, detection Model-B is trained with data set obtained from homogeneous ground and heterogeneous ground. As a result, it is found that the detection Model-B which is trained including heterogeneous ground shows better performance than detection Model-A. It indicates the ground heterogeneity should be considered to increase the performance of automated detection model for GPR exploration.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.10
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• pp.701-708
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• 2022

Since the propellant tank structure of the projectile is mainly subjected to a compressive force, there is a high risk of damage due to buckling. Large and lightweight structures such as propellant tank have a complex manufacturing process. So it requires a non-destructive test method to predict buckling load to use the structure after testing. Many studies have been conducted on Vibration Correlation Technique(VCT), which predicts buckling load using the relationship between compressive load and natural frequency, but it requires a large compressive load to predict the buckling load accurately, and it tends to decrease prediction accuracy with increasing internal pressure in structure. In this paper, we analyzed the causes of the decrease in prediction accuracy when internal pressure increases and proposed a method increasing prediction accuracy under the low compressive load for being usable after testing, through VCT combined testing and FEA result. The prediction value by the proposed method was very consistent with the measured actual buckling load.

• Journal of the Korean Wood Science and Technology
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• v.32 no.2
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• pp.40-49
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• 2004

Phyllostachys pubescens planted in the Nambu Forest Experiment station in Jinju city of Gyongnam province was used, to investigate the physical and mechanical property of bamboo in this study. The ages of the P. pubescens were 1, 2 and 3 years, respectively. This experiment was carried out in August and January. The P. pubescens were divided into upper, middle and lower parts according to the growing points. The physical and mechanical properties of the P. pubescens were investigated before and after treatment of hot water and microwave irradiation. 1. The upper part of the P. pubescens indicated the highest static MOE according to the growing points. The range of the static MOE was from 70,000 to 110,000kgf/cm². 2. When P. pubescens were treated with hot water of 95℃, the ratio of softening was about 10~30%. 3. As microwave irradiation time was increased, the MOE values was decreased in both green and water-saturated bamboos. For the irradiation time of 20 and 30 seconds, the static MOE of P. pubescens was decreased up to about 50% comparing with non-treated.