Advanced Nondestructive Evaluation I

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Authors: Jong Min Kin, Min Sung Hong, Bong Suk Kim, Soo Hun Lee
Abstract: In conventional machining, cutting conditions such as cutting speed, feed rate, and depth of the cut have great influence on the surface roughness. In micro machining, however, the surface shape is affected by not only the machining parameters mentioned earlier but also tool stiffness, system stability, and workpiece properties caused by the miniatured structure and cutting tool. Especially, in a micro-machine system, the difference between the cutting forces in the recursive cuts introduces the vibration easily. A high spindle causes instability of the system, increases the temperature in the cutting process, and also changes the tool’s shape. This study introduces a method to predict the surface shape of the workpiece based on the machining conditions in micro milling. The micro-milled surfaces in different machining conditions are predicted by a computer simulation including the vibration model and the simulated results show good agreement with the experimental results.
Authors: Sung Yong Park, Byung Uk Jeon, Jang Moo Lee, Yong Hyeon Cho
Abstract: The railway contact wire, which supplies electric railways with electric power, plays an important role in determining the maximum railway velocity. In general, the maximum allowable velocity of an electric railway is less than seventy percent of the wave propagation velocity of the contact wire. Because the contact wire is more a beam model with dispersive wave characteristics than a string model, the wave propagation velocity depends on the frequency. For this reason, there have been only few studies on the wave propagation of the contact wire. In this paper, we proposed two useful methods for estimating the wave propagation velocity of the railway contact wire by using the Gabor wavelet transform on the experimental signals. In the first method, the ridges of wavelet transform, which contain the essential information about dispersive characteristics, are used. Specifically, the wave propagation velocity of the contact wire can be extracted from the time difference of the wavelet ridges of the measured signals. In the second method, the cross-correlation analysis of each wavelet transform is used to extract the wave propagation. The selection of the optimal Gabor shaping factor for the best time-frequency localization by using the Shannon entropy cost function is also discussed.
Authors: Min Gi Kim, Won Woo Hwang, Soo Hun Lee
Abstract: As the home appliances are systemized, they have complicatedly assembled structure. It is reasonable to see the noise problem of home appliance in the viewpoint of system like vehicle and ship. There are various system analysis methods to resolve the noise problem [1-3]. To use system analysis methods, the system information like modal and path properties must be gathered and analyzed. But it takes many times to find out the system properties, so the simpler system analysis methods are needed. The coherence analysis method is useful as the system analysis method, since the method can identify the system property like the relationship between inputs and outputs directly and simply. In the paper, the partial coherence analysis is used for identification of the MISO system of washing machine, in which multi-input signals are vibration signals of motor bracket and an output signal is noise signal of washing machine. The relationship between the noise of washing machine and the vibration of the motor bracket in working status was identified and the parts of bracket closely correlated with noise were also proved by the relationship. And the noise of washing machine was controlled by redesigning the parts of bracket associated with the noise of washing machine based on the coherence function in octave band.
Authors: Beom Seok Kim, Seung Hyun Yoo, Sang Jo Lee, Sung Kook Baik
Abstract: The existence of a crack in a structure produces changes in modal parameters of it such as natural frequencies, damping, displacement and strain mode shapes. This paper is focused on characterization of crack detection methods using strain mode shapes. To characterize crack detection methods, we changed sensing grids from corner grid to cross grid and geometry of the specimens from rectangular to triangular plate. Rest of conditions was fixed. For crack detection criteria, COMAC, ECOMAC, ADSM and new method have been used and the results are compared with each other. The COMAC, ECOMAC and ADSM showed limited capacity of crack detection on plates but the new method gave good results in 90% of all cases.
Authors: D.K. Kim, G.H. Jang
Abstract: This research investigates the vibration caused by ball bearing in a HDD spindle system, specifically non-repeatable runout (NRRO), at elevated temperature by analyzing the characteristics of ball bearing and the natural vibration characteristics of the spindle system due to the effect of elevated temperature. It shows that the elevated temperature results in the decrease of bearing deformation in the spindle system, which reduces the bearing stiffness and the natural frequencies of the spindle system consequently. It has a significant effect on the amplitude and the frequency distribution of NRRO at elevated temperature.
Authors: Yong Hyeon Cho, Jang Moo Lee, Sung Yong Park, Eung Shin Lee
Abstract: The aim of this paper is to propose a robust method for extracting damping ratios of a railway contact wire using a continuous wavelet transform (CWT). It is hard to measure the damping ratios of the contact wire because the contact wire has close natural modes in a low frequency range and the dynamic signals of the contact wire gathered in the field are easily corrupted by extraneous noises. The proper choice of the wavelet parameters to decouple the close modes is required in order to obtain accurate damping ratios for the railway contact wire. In this paper, we investigated CWT error terms and derived a relation between a frequency resolution and complex Morlet wavelet parameters. In order to show the accuracy of the proposed method, we extracted damping ratios for the simulated pure and noisy signals which have close natural modes. According to the results, the proposed method can provide the damping ratios well agreed with true ones even for the noisy data. Finally, we applied the proposed method to the contact wire of a conventional railway line in Korea in order to verify the applicability in the field. The damping ratios extracted from the real data were in the range from 0.01 to 0.04.
Authors: Ju Young Yun, Yong Hyeon Shin, Kwang Hwa Chung
Abstract: In examining particulate deposits in the pipes within a chemical vapor deposition (CVD) system, vibration diagnostics is compared and studied against ultrasonic diagnostics. The latter method involves pulsing the outer wall of pipes with an ultrasonic sensor and analyzing the resulting echo to observe particulate deposits inside pipes. Vibration diagnostics examines the existence of particulate deposits by analyzing the difference in the frequencies generated when a vibrator is adhered to the outer wall of pipes. With ultrasonic diagnostics, good test results were obtained only when particulate deposits were attached to the inner wall of the pipes. After some time, however, particulate deposits were not detected properly, as the ultrasonic wave failed to cross the fine gaps created between the inner wall of the pipe and the deposits. In conclusion, the vibration diagnostics is being expected as the effective method in monitoring the particulate deposits inside pipes in the CVD system where the desired behavior is reduced frequency along with the the particulate deposits in comparison to the case where the pipe is clean.
Authors: Sung Soo Jung, S.I. Cho, Young Tae Kim, C.U. Cheong, Ho Chul Kim
Abstract: The image of a semi-circular blockage and location in the uniform and stepped pipe was reconstructed by measuring the eigen-frequency shift of the resonance and anti-resonance frequencies of multi-sine acoustic waves. In this study we have used different boundary conditions from previous works of Wu and Fricke [1] and De Salis and Oldham [2] to determine the blockage cross-sectional area and position. The results agreed with real fractional cross sectional area and position in the both continuous and stepped pipes. New approach showed a better quality of reconstructed image with small ripple number and the false dummy blockage signal was also reduced. The present method of blockage image reconstruction is a noninvasive nondestructive and can meet the integrity evaluation implementation for all types of transmission pipeline
Authors: Hong Hee Yoo, Simon Song, Kang Sik Jung, Kwan Yong Kim
Abstract: Nonlinear modeling method for the structural dynamic analysis of a micro cantilever beam actuated by electrostatic force is presented in this study. Static deflection is first obtained by solving nonlinear static equilibrium equation and the modal and the stability characteristics are calculated at the static equilibrium position. It is found that the amplitude and the frequency of the applied electrostatic voltage influence the stability of the structure significantly.
Authors: Hong Seok Lim, Hong Hee Yoo
Abstract: Flexible structures undertaking impact while undergoing overall motion can be found in several industrial products these days. Transient motion and stress induced by impact should be considered elaborately to extend the life of the products. In the present study, a modeling method for a flexible beam with a tip mass that undertakes impact while undergoes large overall motion is presented. The tip mass takes the impact force and the transient responses of the beam are calculated by employing the assumed mode method. The stiffness variation caused by the large overall motion is considered in this modeling. The effects of the tip mass and the angular speed of the beam on the transient responses are investigated.

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