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ABSTRACT: Thermal spraying processing usually use nickel-aluminum alloy system as major powder due to its strong adhesion to substrates. The contents of powder material and the processing parameters used in the spraying process cause material properties of coating exhibiting a wide variation. It is difficult to investigate mechanical properties of coating layer in nondestructive way. This research focuses on characterizing mechanical properties of thermal spraying coatings at high temperature environment up to 295° C in nondestructive way. A laser ultrasound technique (LUT) is used for the measurements of dispersion spectra of guided waves. Theoretical model for surface waves propagating along a multi-layered structure with coating and substrate is used to model the sprayed coatings. An inversion algorithm based on Shuffled Complex Evolution (SCE-UA) is used to extract mechanical properties from the measured dispersion spectra cooperating with theoretical model. In the results, surface wave dispersion spectra are measured for three different thickness coatings at different temperature environment. The difference thickness of coatings and temperature environment are reacted to dispersion spectrum of guided waves. It also related to mechanical properties of coating in theoretical model. This method is potentially useful to characterize the mechanical properties of thermal spraying coating in a nondestructive way.
The Journal of the Acoustical Society of America 04/2012; 131(4):3476. · 1.55 Impact Factor
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ABSTRACT: This research employs a quantitative laser ultrasound visualization system (QLUVS) for the full-field mechanical property mapping in plate-like structures. The QLUVS has the advantage of fast, full-field and quantitative inspection. The QLUVS uses a pulsed laser generate acoustic waves with fast scanning mechanism to reach two dimensional scanning goal and then detected with a piezoelectric longitudinal transducer. By utilizing QLUVS, the spatial and temporal information of guided wave can be obtained with further signal processing, the velocity map can be extracted. Finally the analytical model and inversion algorithm will be integrated into QLUVS for the full-field mechanical property mapping purpose.
The Journal of the Acoustical Society of America 04/2012; 131(4):3477. · 1.55 Impact Factor
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ABSTRACT: This study employs a theoretical modeling and an experimental measurement for investigating the dispersion behavior of guided waves propagating in a bi-layer system consisting of a piezoelectric plate and a dielectric fluid layer. The theoretical model is based on a recursive asymptotic stiffness matrix method (RASM) with the fluid layer modeled as an equivalent elastic body. A laser ultrasound technique is used to measure the dispersion relations of the bi-layer system. Behaviors of mode couplings between guided modes propagating in the piezoelectric plate and those in fluid layer are characterized in the modeling and measurements. Dispersion behaviors of guided modes propagating in the bi-layer system are discussed for varying fluid thicknesses. For all of the investigated cases, the theoretical modeled dispersion spectra agree well with the measurements.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 08/2011; 58(8):1612-8. · 1.80 Impact Factor
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ABSTRACT: Guided waves propagating in cylindrical tubes are frequently applied for the characterization of material or geometrical properties of tubes. In a tube, guided waves can propagate in the axial direction and called axial guided waves, or in the circumferential direction called circumferential guided waves. Dispersion spectra for the axial and circumferential guided waves share some common behaviors and however exhibit some particular behaviors of their own. This study provides an investigation with theoretical modeling, experimental measurements, and a simplex-based inversion procedure to explore the similarity and difference between the axial guided waves and circumferential guided waves, aiming at providing useful information while axial and circumferential guided waves are applied in the area of material characterization. The sensitivity to the radius curvature for the circumferential guided waves dispersion spectra is a major point that makes circumferential guided waves different from axial guided waves. For the purpose of material characterization, both axial and circumferential guided waves are able to extract an elastic moduli and wall-thickness information from the dispersion spectra, however, radius information can only be extracted from the circumferential guided waves spectra.
Ultrasonics 05/2011; 51(4):472-9. · 1.84 Impact Factor
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ABSTRACT: Acoustic sensors frequently rely on the detection of small mass changes that results from binding of a coated layer coupled
to the active sensor surface. Anti-symmetric flexural (ASF) modes are anti-symmetric type of guided waves propagating along
the tip of wedge-shaped waveguides. Like surface acoustic waves, ASF can be a potential candidate for the purpose of acting
as acoustic sensors. This paper employs a combined numerical and experimental study for the dispersion behaviors of ASF modes
propagating along wedge tips with a layer of coating. The numerical study is based on finite element method while the experimental
study employs a laser ultrasound technique. Velocity for the ASF mode propagating along the wedge tip with a slower coating
is found out to start at the ASF velocity of the matrix wedge at the low frequency regime, and gradually influenced by the
coating as the frequency increases. Enhanced loaded effects from the coating are founded due to the wedge tip geometry. In
general, the numerical results show good agreement with the measurements.
12/2009: pages 377-382;
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ABSTRACT: Solid oxide fuel cell (SOFC) has attracted much attention as a promising source of electrical power generation because of its high efficiency in converting chemical energy to electrical power. The main structure of SOFC is a three-layered ceramic structure with the electrolyte sandwiched by anode and cathode, operating at temperature range of 800-1000°C. In this research, a novel procedure with a laser ultrasound measurement technique and an inversion algorism is developed for the nondestructive characterization of layer properties in the SOFC. Mechanical and geometrical properties of individual layer in the SOFC cell are characterized.
Ultrasonics Symposium (IUS), 2009 IEEE International; 10/2009
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ABSTRACT: Antisymmetric flexural (ASF) modes are antisymmetric types of guided waves propagating along the tip of wedge-shaped waveguides. Acoustic sensors frequently rely on the detection of small mass changes that result from binding a coated layer coupled to the active sensor surface. While a layer is coated on one of the wedge's surfaces, another type of sensor can be potentially developed based on detecting the change of ASF velocity. This paper describes a study on the effects of ASF dispersion behavior for a wedge with a layer of coating using a combined numerical and experimental investigation. In this study, the frequency range is from 0.5 MHz to 10 MHz, and the effective wave propagation length along the wedge tip ranges from 3 mm to 13 mm. Brass wedge tips coated with aluminum layer are studied for the case of slow matrix with fast coating, while aluminum wedge tips with copper coatings are studied for the case of fast matrix/slow coating combination. Like surface acoustic waves propagating along a flat surface with a layer of coating, loaded and stiffened phenomena are observed for the ASF modes traveling along coated wedges. Moreover, the wedge tip geometry is found to have an effect in enhancing the loaded and stiffened phenomena. The numerical results show good agreement with experimental results.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 01/2009; 55(12):2674-82. · 1.80 Impact Factor
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ABSTRACT: This paper describes a laser optical technique for the detection of in-plane (IP) motion of ultrasonic waves propagating in solids. This interference-based laser optical technique includes a tiny square indentation with a width of about 30 microm on the sample surface and a relatively simple optical arrangement. The current technique is applied for the detection of in-plane motions of Lamb waves propagating in a thin brass plate. Measurement of S(0) mode dominated by in-plane motion in the low fd (frequency times thickness) regime is successfully demonstrated with the current technique. The newly proposed non-contact technique provides an alternative other than the heterodyne and Fabry-Perot techniques for the detection of IP motions with a relatively simple optical arrangement. This technique is not readily applicable to general NDE applications, where a position scan or an arbitrary selection of inspection location is needed. However, this technique can be useful in the areas such as fixed-position ultrasound monitoring or laboratory research activities involving optical detection of IP motion.
Ultrasonics 01/2007; 44 Suppl 1:e1239-42. · 1.84 Impact Factor
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ABSTRACT: Wedge waves (WW) are guided acoustic waves propagating along the tip of a wedge, with energy tightly confined near the apex. This study is focused on exploring the dispersion behaviors of WW propagating along a bilinear wedge (BW). A BW is wedge with a cross section of two apex angles, compared with a linear wedge (LW) having a single apex angle. In the literature, many studies regarding to the dispersion behaviors of ASF modes are reported for LW, but not for BW. In this study, a combined experimental and numerical stidy is used to investigate the dispersion behavior of WW propagating in BW's. It is found out that WW in a BW is a result of mode coupling between the two WW's corresponding to simple wedges with the two apex angles of the BW.
Ultrasonics 01/2007; 44 Suppl 1:e1471-4. · 1.84 Impact Factor
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ABSTRACT: This research is focused in the measurement and modeling for the dispersion relations of Lamb waves propagating in LiNbO(3) and LiTaO(3) plates. A theoretical model based on a stiffness matrix method with recursion computation algorism is used to provide numerical calculations for the dispersion relations. Also, a dry, noncontact laser ultrasound technique is used to measured dispersion multi-mode dispersion relations. For all the experiments, the measured dispersion curves show good agreement with the theoretical calculation, indicating the reliabilities in the measurement and modeling.
Ultrasonics 01/2007; 44 Suppl 1:e807-11. · 1.84 Impact Factor
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ABSTRACT: In this research, dispersion behaviors of antisymmetric flexural (ASF) modes propagating along the tip of a bilinear wedge (BW) are investigated. A BW has a cross section with two apex angles, as opposed to a linear wedge (LW) whose cross section has a single apex angle. In the literature, many studies regarding the dispersion behaviors of ASF modes have been reported for LWs, but not for BWs. In this study, laser ultrasonic measurements and finite-element numerical simulations are used to investigate the dispersion behavior of BW-ASF modes. It was found that a BW-ASF mode arises as a result of mode coupling between two LW-ASF modes of the same order corresponding to the two apex angles of the BW.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 05/2006; 53(4):754-60. · 1.69 Impact Factor
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ABSTRACT: This paper describes a laser optical technique that allows the detection of in-plane motion of Lamb waves. This interference-based laser optical technique includes a tiny square indentation with a width of about 30 micron on the sample surface and a relatively simple optical arrangement. The current technique is applied for the detection of in-plane motions of Lamb waves propagating in a 70-micron thick brass plate. Measurement of So mode dominated by in-plane motion in the low fd (frequency times thickness) regime is successfully demonstrated with the current technique. With the indentation replaced by a microreflector in a microelectromechanical (MEMS) structure, this technique is applicable for the detection of in-plane motion in MEMS structures.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 09/2005; 52(8):1372-7. · 1.69 Impact Factor
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ABSTRACT: In this research we report theoretical model and experimental
measurements for the leaky Lamb wave propagation behaviors in a X-cut
lithium niobate immersed in a conductive fluid. Starting with wave
equations, a partial wave analysis procedure is taken for the modeling
of plane wave reflection coefficient, which characterizes the dispersion
relation of piezoelectric plate immersed in a dielectric fluid. Fluid
conductivity is modeled by modeling the fluid as lossy dielectric media.
Bulk wave ultrasonic transducers with V-shape arrangement are used in
this particular experiment, running in pitch-catch manor. Close
comparison with fairly well agreement between theory and measurements is
obtained
Ultrasonics Symposium, 1998. Proceedings., 1998 IEEE; 02/1998
