Key Engineering Materials Vols. 297-300

Abstract: Structural health monitoring (SHM) is a new technology that has been increasingly evaluated by the industry as a potential approach to improve the cost and ease of structural inspection. Piezoelectric smart active layer (SAL) sensor was fabricated to verify the applicability of finding cracks and conducting source location in a various materials. A crack detection and source location works were done in three kinds of test condition such as aluminum plates with crack for patch type SAL sensor, a smart airplane with embedding SAL sensor, and a concrete beam with real crack for practical application. From this experimental study, the evaluation algorithm for the arrival time delay and decrease of signal amplitude was suggested in this paper. Consequently, it was found that the SAL sensor and detection algorithm developed in this study can be effectively used to detect and monitor damages in the both existing structures and new designed smart structures.

Abstract: Structural health monitoring (SHM) is a new technology that has been increasingly evaluated by the industry as a potential approach to improve the cost and ease of structural inspection. Piezoelectric smart active layer (SAL) sensor was fabricated to verify the applicability of finding cracks and conducting source location in a various materials. A crack detection and source location works were done in three kinds of test condition such as aluminum plates with crack for patch type SAL sensor, a smart airplane with embedding SAL sensor, and a concrete beam with real crack for practical application. From this experimental study, the evaluation algorithm for the arrival time delay and decrease of signal amplitude was suggested in this paper. Consequently, it was found that the SAL sensor and detection algorithm developed in this study can be effectively used to detect and monitor damages in the both existing structures and new designed smart structures.

Abstract: The magneto-optical nondestructive inspection system (hereafter refer to as RMO system) using magneto-optical sensor (hereafter refer to as MO sensor) offers the benefits of providing image data and LMF information at the same time. Therefore this system makes it possible to carry out remote and high speed inspection of cracks from the intensity of the reflected light and to estimate the shape of a crack more effectively than by already existing methods. In other words, the shape of crack could be evaluated using image data, and crack depth can be determined by calculating the intensity of reflected light. The purposes of this study were to confirm the vertical components of leakage magnetic flux from a crack using RMO system and to verify the effects of MO sensor using the finite element method and dipole model calculation. The effectiveness of these analysis methods was compared with experiments using a RMO system and several types and sizes of the crack on plate specimens. The volume of a crack could be estimated using the optical intensity regardless of the shape of cracks.

Abstract: The conventional eddy current testing uses a sinusoidal signal with very narrow frequency bandwidth. Whereas, the pulsed eddy current method uses a pulse signal with a broad frequency bandwidth. This allows multi-frequency eddy current testing, and the penetration depth is greater than that of the conventional eddy current testing. In this work, the pulsed eddy current instrument was developed for evaluating the metal loss. The developed instrument was consist of the pulse generator generating the square pulse of maximum 40 V, the amplifier controlled to 52dB, the A/D converter of 16bit 20MHz, and the industrial personal computer for operating with Windows program. And, the probe for the pulsed eddy current was designed as the pancake type in which the sensing coil was located in the driving coil. The peak voltage did not linearly increase with the voltage of the step pulse. For the driving coil with inductance of 670µH, the peak voltage linearly increased with the step pulse voltage to 30V. But, for the other driving coils with the inductance of 1.7mH, 2.7mH, 3.6mH, 22mH, the peak voltage linearly increased with the step pulse voltage to 20V. The output signals of the sensing coil rapidly increased when the step pulse driving voltage was off, and the latter part of the sensing coil output voltage exponentially decreased with a time. The decrement value of the output signals of sensing coil increased with the thickness of the aluminum test piece.

Abstract: X-ray technology has been widely used in a number of industrial applications for monitoring and inspecting inner defects which can hardly be found by normal vision systems as a ball grid array (BGA) or a flip chip array (FCA). Digital tomosynthesis (DT) is one of the most useful X-ray cross-sectional imaging methods for PCB inspection, and it usually uses an X-ray image intensifier. However, the image intensifier distorts X-ray images severely both of shape and intensity. This distortion breaks the correspondences between those images and prevents us from acquiring accurate cross-section images. Therefore, image distortion compensation is one of the most important issues in realizing a DT system. In this paper, an image distortion compensation method for an X-ray DT system is presented. It is to use a general distortion polynomial model on two dimensional plane that can cope with arbitrary, complex and various forms of distortion. Experimental results show a great improvement in compensation speed and accuracy.

Abstract: There is currently a need to evaluate the non-destructive techniques that are used to detect the fracture of stressed steel wires in grouted post-tensioned concrete bridges. Although continuous acoustic emission (AE) monitoring technique has been developed to detect wire breaks in unbonded tendons, it is not established as the on-site monitoring tools for grouted post-tensioned concrete bridges. In this study, AE measurements were conducted to detect corrosion-induced wire fractures inside a grouted post-tensioned beam. The test beam was drilled with 5mm drill bit to expose individual wires and a reservoir filled with corrosive solution of NaCl and NaOH was formed on the side of the beam. During the experiment, the corrosion site was anodically polarized to + 200mV using a potentiostat and it was continuously monitored and the data obtained were processed with an AE monitoring system. The outcome of this research shows that the continuous AE monitoring system successfully identified and located an individual corrosion-induced wire fracture in a fully grouted post-tensioned concrete beam.

Abstract: This paper reports for signal characteristics of before-and-after healing treatment SiC ceramics with crack healing ability. The elastic wave signals generated during the compress load by a Vickers indenter on the brittle materials were recorded in real time, and the waveforms of the individual signals were examined and classified based on their spectral characteristics. The compress loads were applied with the range from 9.8N to 294N. In a bulk SiC specimen, the AE signals occurred only when the load was compressive loading and unloading. But, in the after crack healing specimen of 294N only, even though the external compressive load was stopped and kept on holding constant load states, the AE signals occurred irregularly and continuously. The results of the WT and frequency analysis showed that these existed as the property of frequency in the limited range between 100kHz and about 200kHz. Three-point bending test was performed for the cracked and healed SiC specimens. Consequently the bending strength of the crack healed specimens was recovered completely, but most of the samples with the crack healed showed that the properties of the dominant frequency were comparatively lower than that of the bulk SiC samples. The classification of the wave signals can be used to develop algorithms for autonomous health monitoring systems of brittle material structures.

Abstract: The researches using the Eddy Current Test (ECT) were limited for the particle reinforced metal base composites. It had been impossible to inspect the eddy current since the carbon/epoxy tube had the low electric conductivity of resin layer. However, it has been successful for our previous research to inspect the defect using the EC. In the case of loading to carbon/epoxy tube, the researches of relationship between the failure behavior and the variation of EC signals have not been carried out. Therefore, this research focused on the comparison and the evaluation of the EC signals according to the variation of the defect depth using the unloading and the radial-loading carbon/ epoxy tube. We obtained results are as follow. Firstly, reviewing the stress distribution of carbon/ epoxy tube under the radial-loading, it was known that the defect depth did not have strongly influence on the stress distribution. Therefore, it was believed that the stress distribution was not directly related to the signals of the EC. Secondly, the EC signals similar to that of the unloading specimens could be obtained from the radial-loading specimen of 80 % defect depth. Thirdly, regardless of the unloading and the radial-loading specimens, the defect of 80 % and 100 % depths had the similar phase angles and Lissajous figures. Finally, it was guessed that the length of microcracks distributed at the whole specimens under the radial-loading was less than 60 % defect depth.

Abstract: In this paper, the dispersion curves of a bent cylindrical pipe are obtained by using the 3-dimensional finite element modeling and 2-dimenstional Fourier transform. The transient responses of the bent pipe are calculated by using a general-purpose finite element program, and the displacements are extracted at a series of sequential points as a function of spatial position and time, u(x,t). Then 2-dimentional FFT of u (x,t) offers U (k,ω), the relation between wave number and angular frequency so that the phase velocity and group velocity can be calculated. In addition, verification of the result is made by the mode identification using wavelet transform. The modes invoked by both methods agree very well.