• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.4
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• pp.411-421
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• 2002

The accurate analysis of ultrasonic wave propagation and scattering plays an important role in many aspects of nondestructive evaluation. A numerical analysis makes it possible to perform parametric studies, and in this way the probability of detection and reliability of test results can be improved. In this study, a finite element method was developed for the analysis of ultrasonic fields, the accuracy of results was checked by solving several representative problems. The size of element and the integral time step, which are the critical components for the convergence of numerical results, were determined in a commercial finite element code. Several propagation and scattering problems in 2-D isotropic and anisotropic materials were solved and their results were compared with known analytical or experimental results.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.46 no.3
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• pp.248-252
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• 2001

Near infrared spectroscopy (NIRS) is a rapid and accurate analytical method for determining the composition of agricultural products and feeds. An important merit of the NIRS analytical system is consistent predictions across instruments. However, proper calibration is the most important factor for a NIRS analytical system. Forty samples were obtained from Kyonggi-do Agricultural Research and Extension Services, and used to develop calibrations for crude protein content and crude oil content. Calibrations equations were developed using multiple linear regression (MLR). Accuracy and precision of NIRS predictions were adequate for quality measurement for the two constituents in kidney bean seed. In calibration sample sets (N=30), multiple correlation coefficient between NIR and lab measurements is 0.90 for seed, 0.97 for powder in seed protein concentration and 0.40 for seed and 0.92 for powder in seed oil concentration, respectively. It is concluded that NIRS method is suitable for the determination of seed composition in whole kidney bean.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.306-314
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• 2006

Instrumented indentation technique is a new way to evaluate nondestructive such mechanical properties as flow properties, residual stress and fracture toughness by analyzing indentation load-depth curves. This study evaluated quantitatively the flow properties of steels and residual stress of weldments. First, flow properties can be evaluated by defining a representative stress and strain from analysis of deformation behavior beneath the rigid spherical indenter and the parameters obtained from instrumented indentation tests. For estimating residual stress, the deviatoric-stress part of the residual stress affects the indentation load-depth curve, so that by analyzing the difference between the residual-stress-induced indentation curve and residual-stress-free curve, the quantitative residual stress of the target region can be evaluated. The algorithm for flow property evaluation was verified by comparison with uniaxial tensile test and the residual stress evaluation model was compared to mechanical cutting and ED-XRD results.

• Analytical Science and Technology
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• v.11 no.6
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• pp.448-451
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• 1998

The feasibility of using FT-NIR (Fourier Transform Near Infrared) spectrometer to measure NaOH, $Na_2CO_3$ and $Na_2S$ concentration in a naphtha cracking process, and an outline of the method development to identify spectral feature of the hydroxide whose band is overlapped by a strong water absorption were demonstrated. For measuring NaOH, $Na_2CO_3$ and $Na_2S$, FT-NIR spectrometer is a rapid and possible alternative to the current titration method with a standard deviation of 0.1.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.48-56
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• 2022

Controlling the setting time of cementitious materials is one of the most important factors in securing early-age performance of concrete structures. Recently, the use of retarding admixtures, which enable the inhibition of some hydration products to control the securing time due to average temperature rise is suggested. Although various non-destructive evaluation methods have been proposed to evaluate cement hydration and hardening of cement-based materials to overcome the limitations of Vicat needle test, experimental research is still required to use the non-destructive evaluation method with added retarding admixtures. In this study, measurements of electrical resistivity and ultrasonic wave velocity in early-aged cement pastes were performed according to the addition of retarding admixture(tartaric acid). The setting time of the cement pastes was evaluated by obtained rising time of the both non-destructive measurements. As a result, the possibility of evaluating the setting delay in cement pastes was confirmed through comparative analysis with the initial and final setting times by Vicat test. In addition, X-ray diffraction results at the rising time of electrical resistivity showed a key hydration product affecting the setting delay.

• Journal of Conservation Science
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• v.26 no.1
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• pp.77-83
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• 2010

The damage from the underground termite cannot be discovered with peculiar appearance of building but hollow phenomenon will occur. But there is no case in Korea as a non-destructive measurement of termite activation. Therefore, this research constructs non-destructive diagnostic techniques for wooden cultural properties using microwave detector (Termatrac, Australia). Result of maximun distance were measured 16cm (Pine tree, sensitivity 5, 6), 17cm (Zelkova and Douglas fir, sensitivity 5, 6). These results are expected that can be applied in the field. Result of field test using microwave detector, 33.8% of the wooden cultural properties were damaged by termites, and until now 7.8% (18 buildings) are being damaged in nationwide (total 231 buildings). Based on the above results, microwave detector will be able to be utilized effectively for detecting termite, preventing intrusion in wooden structure, and making full use of monitoring system periodically. In addition, it could be of great worth in preventing insect and microorganism in wooden structure.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.132-139
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• 2002

The grain size of aluminum alloy was refined to the submicrometer level by using equal-channel angular pressing(ECAP). The effect of grain size refinement was evaluated by the tensile test, micro-hardness test, microstructure observations, ultrasonic test and acoustic emission test. The strength and the Vickers hardness were increased significantly according to grain size refinement after equal-channel angular pressed. The ultrasonic velocity was faster after equal-channel angular pressed, and the high frequency range appeared. The results of the ultrasonic velocity and the frequency range are expected to be basic data that can prove the grain size refinement

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.2
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• pp.122-129
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• 2006

Shearography is one of optical methods that has been applied to nondestructive testing (NDT) and strain/stress analysis. The technique has the merit of the directly measuring relative displacement, which is insensitive to environmental vibration disturbance. Previous studies about the method have emphasized on extending its application to new fields and lack insufficient research on effective parameters for qualitative and quantitative evaluation of defects. In this paper, the influence of shearing amount on the detection of an internal defect is investigated. In experiment, slender defects along longitudinal direction of pipeline are artificially designed and detection results according to the change of shearing amount are analyzed. Based on the investigation, we propose the technique for the determination of defect size and accurate source location.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.2
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• pp.108-114
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• 2006

Transient and asymmetric density distributions of butane flow have been investigated from laser image signals by developed three-dimensional digital speckle tomography. Moved signals of speckles have been captured by multiple CCD images in three angles of view simultaneously because the flows were asymmetric and transient. The signals of speckle movements between no flow and downward butane flow from a circular half opening have been calculated by a cross-correlation tracking method so that those distances can be transferred to deflection angles of laser rays fur density gradients. The three-dimensional density fields have been reconstructed from the fringe shift signal which is integrated from the deflection angle by a real-time multiplicative algebraic reconstruction technique (MART).

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.1
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• pp.75-82
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• 2007

As one of the main support systems, rock bolts play a crucial role in the reinforcement of tunnels. Numerical and experimental studies using a transmission method of ultrasonic guided waves are performed to evaluate the integrity of rock bolts encapsulated by grouting paste. Numerical simulations using "DISPERSE" are carried out for the selection of the optimal experimental setup, i.e. non-destructive testing (NDT) system of the rock bolt. Based on results of the numerical simulation, the calculated frequency range for NDT testing is between 20kHz and 70kHz with the first longitudinal L(1) mode. Laboratory transmission tests are performed by attaching the piezo electric sensor at the tip of the rock bolt before embedding. Both of analytical and experimental results show that the amplitude of signals as well as the wave velocity increases with increase in the defect ratio of grouting paste. The defect in grouting paste means that the space around the rock bolt is not fully filled with the grouting paste. Experimental results also show that the increase of the wave velocity is more sensitive to the defect ratio increase than that of the amplitude. This study demonstrates that the transmission technique of ultrasonic guided waves may be a valuable tool in the evaluation of the rock bolt integrity.