• 한국농공학회논문집
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• 제60권6호
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• pp.111-119
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• 2018

The air-void is known to be one of the influencing factors for estimating long-term performance of asphalt concrete. Most of all, confirming air void or density of pavement layer is important for quality control of field compaction level of asphalt concrete pavement. In this study, a non-nuclear type non-destructive density gage (NDDG) was used to estimate compacted air-voids of asphalt pavement as a non-destructive test method. Asphalt concrete slab specimens were prepared using 6 types of asphalt mixes in laboratory (lab) for lab NDDG test. Four different base structure materials were used to find out if there were any differences due to the type of base structure materials. The actual air-voids and NDDG air-voids were measured from 6 asphalt concrete slabs. Four sections of field asphalt pavements were tested using the NDDG, and actual air voids were also measured from field cores taken from the site where the NDDG air-void was measured. From lab and field experimental tests, it was found that the air-voids obtained by NDDG were not the same as the actual air-voids measured from the asphalt concrete specimen. However, it was possible to estimate air voids based on the relationship obtained from regression analysis between actual and NDDG air voids. The predicted air-voids based on the NDDG air-voids obtained from 50mm depth were found to be reliable levels with $R^2{\fallingdotseq}0.9$. Therefore, it was concluded that the air-voids obtained from NDDG could be used to estimate actual air-voids in the field asphalt pavement with a relatively high coefficient of determination.

• 한국해양공학회지
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• 제35권5호
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• pp.327-335
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• 2021

Microcracks can rapidly grow and develop in high-strength steels used in offshore structures. It is important to render these microcracks harmless to ensure the safety and reliability of offshore structures. Here, the dependence of the aspect ratio (As) of the maximum depth of harmless crack (a_hlm) was evaluated under three different conditions considering the threshold stress intensity factor (Δk_th) and residual stress of offshore structural steel F690. The threshold stress intensity factor and fatigue limit of fatigue crack propagation, dependent on crack dimensions, were evaluated using Ando's equation, which considers the plastic behavior of fatigue and the stress ratio. a_hlm by peening was analyzed using the relationship between Δk_th obtained by Ando's equation and Δk_th obtained by the sum of applied stress and residual stress. The plate specimen had a width 2W = 12 mm and thickness t = 20 mm, and four value of As were considered: 1.0, 0.6, 0.3, and 0.1. The a_hlm was larger as the compressive residual stress distribution increased. Additionally, an increase in the values of As and Δk_th(l) led to a larger a_hlm. With a safety factor (N) of 2.0, the long-term safety and reliability of structures constructed using F690 can be secured with needle peening. It is necessary to apply a more sensitive non-destructive inspection technique as a non-destructive inspection method for crack detection could not be used to observe fatigue cracks that reduced the fatigue limit of smooth specimens by 50% in the three types of residual stresses considered. The usefulness of non-destructive inspection and non-damaging techniques was reviewed based on the relationship between a_hlm, a_NDI (minimum crack depth detectable in non-destructive inspection), a_{cr N} (crack depth that reduces the fatigue limit to 1/N), and As.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.622-628
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• 2004

In general, Reinforced Slopes by Shotcrete are difficult to inspect because of stiff Slope and highly Working Area. So the Inspection Techniques are needed by the Non-contact and Non-destructive. On this Study, Appling the safety method to finding the weak zones(cavity area, dampness area, etc.) by using the Infrared Thermal Technique That is detecting the Detail Thermal Difference on the Surface of Reinforced Slopes by Shotcrete.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 춘계학술대회 논문집
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• pp.239-244
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• 1998

ESP(Electronic Speckle Pattern Interferometry) is an optical technique to measure deforamtion of engineering components and materials in industrial areas. ESPI, a non-contact and non-destructive measuring method, is capable of providing full-field results with high spatial resolution and high speed. One of important application aspects using electronic speckle pattern interferometry is to generate contours of a diffuse object in order to provide data for 3-D shape analysis and topography measurement. The electronic speckle contouring is suitable for providing measurement range from millimeters to several centimeters. In this study, we introduce the contouring method by modified dual-beam speckle pattern interferometer and a shift of the two illumination beams through optical fiber in order to obtain the contour fringe patterns. Before the experiments, we performed the geometric analysis for dual-beam-shifted ESPI contouring. And by this geometric analysis, we performed the electronic speckle contouring experiment. We used 4-frame phase shifting method with PZT for quantitative analysis of contour fringes. Finally, we showed good agreements between the geometric analysis and experimental results.

• Steel and Composite Structures
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• 제41권5호
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• pp.681-695
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• 2021

Many existing transmission or communication towers designed several decades ago have undergone nonreversible performance degradation, making it hardly meet the additional requirements from upgrades in wind load design codes and extra services of electricity and communication. Therefore, a new-type non-destructive reinforcement method was proposed to reduce the on-site operation of drilling and welding for improving the quality and efficiency of reinforcement. Six built-up steel angle members were tested under compression to examine the reinforcement performance. Subsequently, the cyclic loading test was conducted on a pair of steel angle tower sub-structures to investigate the reinforcement effect, and a simplified prediction method was finally established for calculating the buckling bearing capacity of those new-type retrofitted built-up steel angles. The results indicates that: no apparent difference exists in the initial stiffness for the built-up specimens compared to the unreinforced steel angles; retrofitting the steel angles by single-bolt clamps can guarantee a relatively reasonable reinforcement effect and is suggested for the reduced additional weight and higher construction efficiency; for the substructure test, the latticed substructure retrofitted by the proposed reinforcement method significantly improves the lateral stiffness, the non-deformability and energy dissipation capacity; moreover, an apparent pinching behavior exists in the hysteretic loops, and there is no obvious yield plateau in the skeleton curves; finally, the accuracy validation result indicates that the proposed theoretical model achieves a reasonable agreement with the test results. Accordingly, this study can provide valuable references for the design and application of the non-destructive upgrading project of steel angle towers.

• 보존과학회지
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• 제35권6호
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• pp.631-640
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• 2019

본 연구는 전통제철법인 정련 및 단접을 적용한 사철강괴(SI)의 미세조직을 파괴분석법인 현미경분석과 비파괴분석법인 중성자 영상 분석을 통해 분석결과를 비교하였다. 시료는 전통제철법으로 생산한 사철강괴이며, 파괴분석용의 SI-A와 비파괴분석용의 9 ㎠의 SI-B를 제작하였다. 파괴분석으로 금속현미경과 주사전자현미경이 이용되었으며, 비파괴분석으로 일본 훗카이도 대학의 소형 중성자원 이용시설을 통한 중성자 영상 분석을 이용하였다. 파괴분석결과 미세한 ferrite 및 pearlite가, 시료의 가장자리에서 Widmanstätten ferrite와 조대한 ferrite가 관찰되었다. 또한 비파괴분석법인 중성자 영상 분석 결과 체심입방격자 구조의 grain size가 3 ㎛ 정도의 α-Fe인 ferrite와 층상의 pearlite가 관찰되었다. 이렇듯 중성자 영상 분석을 이용하면 비파괴로 연구대상의 재료과학적 특성을 확인할 수 있고 문화재에 적용 시 최적의 연구결과를 얻을 수 있음을 확인하였다.

• Current Optics and Photonics
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• 제4권1호
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• pp.31-43
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• 2020

The feasibility of the application of terahertz electromagnetic waves in the diagnosis of prostate cancer was examined. Four samples of incomplete cancerous prostatic paraffin-embedded tissues were examined using terahertz spectral imaging (TPI) system and the results obtained by comparing the absorption coefficient and refractive index of prostate tumor, normal prostate tissue and smooth muscle from one of the paraffin tissue masses examined were reported. Three hundred and sixty cases of absorption coefficients from one of the paraffin tissues examined were used as raw data to classify these three tissues using the Principal Component Analysis (PCA) and Least Squares Support Vector Machine (LS-SVM). An excellent classification with an accuracy of 92.22% in the prediction set was achieved. Using the distribution information of THz reflection signal intensity from sample surface and absorption coefficient of the sample, an attempt was made to use the TPI system to identify the boundaries of the different tissues involved (prostate tumors, normal and smooth muscles). The location of three identified regions in the terahertz images (frequency domain slice absorption coefficient imaging, 1.2 THz) were compared with those obtained from the histopathologic examination. The tissue tumor region had a distinctively visible color and could well be distinguished from other tissue regions in terahertz images. Results indicate that a THz spectroscopy imaging system can be efficiently used in conjunction with the proposed advanced computer-based mathematical analysis method to identify tumor regions in the paraffin tissue mass of prostate cancer.

• Journal of the Korean Statistical Society
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• 제7권1호
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• pp.27-43
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• 1978

This paper deals with the problem of obtaining a minimum cost acceptance sampling plan for destructive testing. The cost model is constructed under the assumption that the sampling procedure takes the following form; 1) lots rejected on the first sample are acreened with a non-destructive testing, 2) the screening is assumed to be imperfect, and therefore, after the screening, a second sample is taken to determine whether to accept the lot of to scrap it. The usual sampling procedures for destructive testing can be regarded as special cases of the above one. Utilizing Hald's Bayesian approach, procedures for finding the global optimal sampling plans are given. However, when the lot size is large, the global plan is very different to obtain even with the aid of an electronic computer. Therefore a method of finding suboptimal plan is suggested. An example with uniform prior is also given.

• Corrosion Science and Technology
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• 제2권6호
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• pp.266-271
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• 2003

Safety diagnosis of various structural components and facilities is indispensable for preventing catastrophic failure of material by time-dependent and environment accelerating degradation. Also, this diagnosis of operating components should be done periodically for safe maintenance and economical repair. However, conventional standard methods for mechanical properties have the problems of bulky specimen, destructive procedure and complex procedure of specimen sampling. So, a non-destructive and simple mechanical testing method using small specimen is needed. Therefore, an advanced indentation technique was developed as a potential method for non-destructive testing of in-field structures. This technique measures indentation load-depth curve during indentation and analyzes the mechanical properties related to deformation such as yield strength, tensile strength and work-hardening index. In this paper, we characterized the tensile properties including yield and tensile strengths of the V-modified Cr-Mo steels in petro-chemical and thermo-electrical plants. And also, the effects of hydrogen-assisted degradation of the V-modified Cr-Mo steels were analyzed in terms of work-hardening index and yield ratio.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.42-50
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• 2008

To evaluate rock bolt integrity, destructive test such as pull-out test has been commonly carried out. This method is known as time consuming, expensive, and inaccurate procedure. To improve destructive method, non-destructive techniques using transmitted guided ultrasonic waves were suggested. Note for the transmission method, the source for the generation of ultrasonic waves should be installed during the rock bolt construction. The purpose of this study is to investigate the reflection method using reflected guided ultrasonic waves to evaluate the integrity of the rock bolt grouted, and to compare the results evaluated by the reflection and transmission methods. The guided waves are generated by PZT element and received by AE sensor. The measured signals are analyzed by the wavelet transform. The results show that the energy velocities of guided ultrasonic waves increase with the defect ratio in both transmission and reflection method. The reflection method produces the lower velocity in all defect ratio. This research demonstrates that the reflection method may be suitable and easer method for the field tests.