• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.90-95
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• 2007

Single side final polishing is a very important role to stabilize a wafer finally before the device process on the wafer is executed. In this study, the machining variables, such as pressure, machining time, and the velocity of pad table were adopted. These parameters have the major influence on the characteristics of wafer polishing. We investigated the surface roughness changing these variables to find the optimal polishing condition. Pad, slurry, slurry quantity, and oscillation distance were set to the fixed variables. In order to reduce defects and find a stable machining condition, a hall sensor was used on the polishing process. AE sensor was attached to the polishing machine to verify optimal condition. Applying data analysis of the sensor signal, experiments were performed. We can get better surface roughness from loading the quasi static force and improving wafer-holding method.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.218-223
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• 1999

A piezoelectric flextentional deep-water sonar transducer has been simulated using a coupled FE-BEM. The dynamics of the sonar transducer is modelled in three dimensions and is analyzed with extern리 electrical excitation conditions as well as external acoustic pressure loading conditions. Different results are available such as steady-state frequency response for RX and TX, displacement modes, directivity patterns, back-scattering patterns, resonant frequencies, bandwidths, quality factors, transmitting voltage (TV) responses, input receiving sensitivity (RS) responses. White the present barrel-stave typed sonar transducer of the piezoelectric material is being simulated, the external surface of the transducer is modified in order to allow the same water pressure to be applied to the inner and the outer surfaces of the transducer. With this modification for deep-water application, the resonance frequency of the modified flextentional sonar transducer becomes much lower than that of the unmodified flextentional sonar transducer. The results of the present sonar transducer modelling are also compared with those of a commercial package such as ATILA.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.362-367
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• 2008

In the present work, we address electric fatigue behavior in bending piezoelectric actuators using an acoustic emission technique. Electric cyclic fatigue tests have been performed up to ten million cycles on the fabricated specimens. To confirm the fatigue damage onset and its pathway, the source location and distributions of the AE behavior in terms of count rate are analyzed over the fatigue range. It is concluded that electric cyclic loading leads to fatigue damages such as transgranular damages and intergranular cracking in the surface of the PZT ceramic layer, and intergranular cracking even develops into the PZT inner layer, thereby degrading the displacement performance. The electric-induced fatigue behavior seems to show not a continuous process but a step-by-step process because of the brittleness of PZT ceramic. Nevertheless, this fatigue damage and cracking do not cause the final failure of the bending piezoelectric actuator loaded up to 107 cycles. Investigations of the AE behavior and the linear AE source location reveal that the onset time of the fatigue damage varies considerably depending on the existence of a glass-epoxy protecting layer.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.407-412
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• 2001

In this research, damage behavior of singly oriented ply (SOP) fiber metal laminate (FML) subject to concentrated load was studied. The static indentation tests were conducted to study fiber orientation effect on damage behavior of FML. During the static indentation tests, Acoustic Emission technique (AE) was adopted to study damage characteristics of FML. AE signals were obtained by using AE sensor with 150kHz resonance frequency and the signals were compared with indentation curves of FML. As fiber orientation angle increases, the crack initiation load of SOP FML increases because the stiffness induced by fiber orientation is increased. The penetration load of SOP FML is influenced by the deformation tendency and boundary conditions. Cumulative AE counts were well predicted crack initiation and crack propagation and AE amplitude were useful for prediction of damage failure mode. During the matrix cracking, fiber debonding and fiber breakage, AE amplitude has $45{\sim}60dB,\;60{\sim}80dB\;and\;90{\sim}100dB$, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.10
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• pp.1048-1053
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• 2002

In this paper, thin film bulk acoustic resonator(TFBAR) lattice and balanced type filter topologies are designed and fabricated. Aluminium nitride and platinum are used for piezoelectric material and top and bottom electrodes, respectively. Air-gap is placed to avoid silicon substrate loading effect and the performance of these lattice and balanced filters is compared with ladder filters. These filters have selectivity over 15 dB for lattice type and 30 dB for balanced type and reveal wider bandwidth of the ladder filters. For balanced type filters, minor tuning procedure is not needed and they are readily available for RF filter in wireless applications.

• Geomechanics and Engineering
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• v.23 no.6
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• pp.503-512
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• 2020

Mining activities focus on the production of mineral resources for energy generation and raw material requirements worldwide and it is a known fact that shallow reserves become scarce. For this reason, exploration of new resources proceeds consistently to meet the increasing energy and raw material demand of industrial activities. Rock mechanics has a vital role in underground mining and surface mining. Devices and instruments used in laboratory testing to determine rock mechanics related parameters might have limited sensing capability of the failure behavior. However, methodologies such as, thermal cameras, digital speckle correlation method and acoustic emission might enable to investigate the initial crack formation in detail. Regarding this, in this study, thermographic analysis was performed to analyze the failure behaviors of different types of rock specimens during uniaxial compressive strength experiments. The energy dissipation profiles of different types of rocks were characterized by the temperature difference recorded with an infrared thermal camera during experiments. The temperature increase at the failure moment was detected as 4.45℃ and 9.58℃ for andesite and gneiss-schist specimens, respectively. Higher temperature increase was observed with respect to higher UCS value. Besides, a temperature decreases of about 0.5-0.6℃ was recorded during the experiments of the marble specimens. The temperature change on the specimen is related to release of radiation energy. As a result of the porosity tests, it was observed that increase in the porosity rate from 5.65% to 20.97% can be associated to higher radiation energy released, from 12.68 kJ to 297.18 kJ.

• Geomechanics and Engineering
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• v.24 no.1
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• pp.81-89
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• 2021

Uniaxial compression tests were conducted on sandstone-CGFB composite samples with different interface angles, and their strength, acoustic emission (AE), and failure characteristics were investigated. Three macro-failure patterns were identified: the splitting failure accompanied by local spalling failure in CGFB (Type-I), the mixed failure with small sliding failure along with the interface and Type-I failure (Type-II), and the sliding failure along with the interface (Type-III). With an increase of interface angle β measured horizontally, the macro-failure pattern changed from Type-I to Type-II, and then to Type-III, and the uniaxial compressive strength and elastic modulus generally decreased. Due to the small sliding failure along with the interface in the composite sample with β of 45°, AE events underwent fluctuations in peak values at the later post-peak failure stage. The composite samples with β of 60° occurred Type-III failure before the completion of initial compaction stage, and the post-peak stress-time curve initially exhibited a slow decrease, followed by a steep linear drop with peaks in AE events.

• Structural Engineering and Mechanics
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• v.89 no.3
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• pp.265-281
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• 2024

The sound radiation responses of multi-layer composite plates subjected to harmonic mechanical excitation in hygrothermal environment is numerically investigated. A homogenized micromechanical finite element (FE) based on the higher-order mid-plane kinematics replicating quadratic function as well as the through the thickness stretching effect together with the indirect boundary element (IBE) scheme has been first time employed. The isoparametric Lagrangian element (ten degrees of freedom per node) is used for discretization to attain the hygro-thermo-elastic natural frequencies and the modes of the plate via Hamilton's principle. The effective material properties under combined hygrothermal loading are considered via a micromechanical model. An IBE method is then implemented to attain structure-surrounding coupling and the Helmholtz wave equation is solved to compute the sound radiation responses. The effectiveness of the model is tested by converging it with the similar analytical/numerical results as well as the experimentally acquired data. The present scheme is further hold out for solving diverse numerical illustrations. The results revealed the relevance of the current higher-order FE-IBE micromechanical model in realistic estimation of hygro-thermo-acoustic responses. The geometrical parameters, volume fraction of fiber, layup, and support conditions alongside the hygrothermal load is found to have significant influence on the vibroacoustic characteristics.

• The Korean Journal of Petroleum Geology
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• v.9 no.1_2 s.10
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• pp.16-23
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• 2001

The study area in the East Sea is located on the northeastern margins of the Ulleung Basin near the Kita-Yamato Bank. The research area provides the important clue to the development of Miocene basins which are characterized by the normal faults and volcanic activities related to rifting in the continental crust. Kita-Yamato Bank is a small sediment-filled graben which was formed by failed rifting in the Early Miocene. The basins rapidly vary the bathymetry, depth of acoustic basement and thickness of sedimentary layer. The tension in the study area caused the extensional lithospheric deformation before/during the Early Miocene. In consequence, tectonic forces resulted in the depression or subsidence of basement from continental rifting in the Kita-Yamato Bank followed by the opening of the Ulleung Basin, and caused the onset of graben or half-graben structure bounded by large blocked syn-rift faults. Afterward no significant tectonic deformation exists, with the consequence that post-rift normal faults with small heave were formed and reactivated by the resultant forces such as tectonic subsidence, sediment loading and volcanic activity. The Cenozoic sediment layer has a maximum thickness of 1.0 s along the center of the graben or half-graben, which overlies the consolidated acoustic basement. Seismic units V and IV supposed to be syn-rift sedimentary rocks are deformed by both the volcanic activities and numerous basement-involved normal faults induced from extension. In the uppermost layer, slump scars resulted from the slope failure are recognized.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.5
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• pp.532-538
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• 2002

This study was performed to classify the fatigue crack opening and closure for three kinds of aluminum alloy using principal component analysis (PCA). Fatigue cycle loading test was conducted to acquire AE signals which come from different source mechanisms such as crack opening and closure, rubbing, fretting etc. To extract the significant feature from AE signal, correlation analysis was performed. Over 94% of the variance of AE parameters could accounted for the first two principal components. The results of the PCA on AE parameters showed that the first principal component was associated with the size of AE signals and the second principal component was associated with the shape of AE signals. An artificial neural network (ANN) an analysis was successfully used to classify AE signals into six classes. The ANN classifier based on PCA appeared to be a promising tool to classify AE signals for fatigue crack opening and closure.