Adaptive and Automatic Detection of Resonant Frequencies in Resonant Ultrasound Spectroscopy Spectra PDF Download

Author: Md. Rafiqul I. Sarker
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Category : Additive manufacturing
Languages : en
Pages : 0

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Languages : en
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A resonant ultrasound spectroscopy method provides a unique characterization of an object for use in distinguishing similar objects having physical differences greater than a predetermined tolerance. A resonant response spectrum is obtained for a reference object by placing excitation and detection transducers at any accessible location on the object. The spectrum is analyzed to determine the number of resonant response peaks in a predetermined frequency interval. The distribution of the resonance frequencies is then characterized in a manner effective to form a unique signature of the object. In one characterization, a small frequency interval is defined and stepped though the spectrum frequency range. Subsequent objects are similarly characterized where the characterizations serve as signatures effective to distinguish objects that differ from the reference object by more than the predetermined tolerance.

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Languages : en
Pages : 10

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All objects exhibit vibrational resonances when mechanically excited. These resonant frequencies are determined by density, geometry, and elastic moduli. Resonant ultrasound spectroscopy (RUS) takes advantage of the known relationship between the parameters. In particular, for a freely suspended object, with three of the four parameters (vibrational spectra, density, geometry, or elastic moduli) known the remaining one can be calculated. From a materials characterization standpoint it is straight-forward to measure density and geometry but less so to measure all the elastic moduli. It has recently become possible to quickly and accurately measure vibrational spectra, and using code written at Los Alamos, calculate all the elastic moduli simultaneously. This is done to an accuracy of better than one percent for compression and 0.1 percent for shear. RUS provides rapid acquisition of materials information here-to-fore obtainable only with difficulty. It will greatly facilitate the use of real materials properties in models and thus make possible more realistic modeling results. The technique is sensitive to phase changes and microstructure. This offers a change to input real data into microstructure and phase change models. It will also enable measurement of moduli at locations in and about a weld thus providing information for a validating coupled thermomechanical calculations.

Author: Gautham Manoharan
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Languages : en
Pages : 67

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The objective of this thesis is to validate Resonant Ultrasound Spectroscopy (RUS) as a non-destructive evaluation tool that can be used to study effects of radiation on the mechanical properties of a material, mainly its elastic constants. RUS involves experimentally measuring the resonant frequencies of a sample and calculating the elastic constants based on these measurements. Finite Element Method (FEM) is used to get the frequencies of the modes of free vibration for the sample model. This result depends on the elastic constant values used in the FEM simulation. Studies were conducted to confirm the accuracy of the FEM model, and determine the right configuration and parameters to use for the simulation. Assuming uniform and isotropic elastic property changes, the effects of radiation damage can be quantified by obtaining a set of matching resonant frequencies between the experimental and FEM simulation results, before and after irradiating the sample. This is done by adjusting the elastic constant values used in the simulation so that the results match with the experimentally obtained resonant frequencies. With powerful enough equipment, even real time monitoring is possible in harsh environments, thus pointing out imminent failure.

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Languages : en
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A new non-contact resonant ultrasound spectroscopic technique is employed to determine the response characteristics of spherical fusion targets, with particular emphasis on both the displacement sensitivity and frequency response of the technique. The optical experimental method is based on photorefractive optical lock-in detection scheme with narrow bandwidth amplification to measure phase variations in light scattered from optically rough, continuously vibrating surfaces with very high, linear sensitivity and a noise level on the order of 10.6 nanometers RMS. This high sensitivity is needed to determine the vibrational modes of the gas inside an spherical target separately from the elastic modes of the containment shell. These measurements can be used to calculate the pressure and density of the internal gas. This approach is also used to discriminate between nearly-degenerate resonant modes characteristic of the frequency spectrum when the target fabrication is inadequate (non-uniform shell thickness, misalignment of hemispheres) or when the Deuteriumrrritium solid fuel inside the target is not symmetrically distributed at cryogenic temperatures. Asymmetries in the fuel layering and geometric perturbations disturb the target implosion process creating deleterious effects in fusion energy generation. The technique is applied to determine the modal characteristics of a target sphere with known response from 100 KHz to 450 KHz. The results demonstrate the unique capabilities of the optical lock-in detection method to measure very small resonant ultrasonic signals.

Author: 鄭鴻輝
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Category :
Languages : en
Pages : 95

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Languages : en
Pages : 19

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This paper describes resonant ultrasound spectroscopy (RUS) as a powerful and established technique for measuring elastic constants of a material with general anisotropy. The first step of this technique consists of extracting resonance frequencies and damping from the vibrational frequency spectrum measured on a sample with free boundary conditions. An inversion technique is then used to retrieve the elastic tensor from the measured resonance frequencies. As originally developed, RUS has been mostly applicable to (i) materials with small damping such that the resonances of the sample are well separated and (ii) samples with simple geometries for which analytical solutions exist. In this paper, these limitations are addressed with a new RUS approach adapted to materials with high damping and samples of arbitrary geometry. Resonances are extracted by fitting a sum of exponentially damped sinusoids to the measured frequency spectrum. The inversion of the elastic tensor is achieved with a genetic algorithm, which allows searching for a global minimum within a discrete and relatively wide solution space. First, the accuracy of the proposed approach is evaluated against numerical data simulated for samples with isotropic symmetry and transversely isotropic symmetry. Subsequently, the applicability of the approach is demonstrated using experimental data collected on a composite structure consisting of a cylindrical sample of Berea sandstone glued to a large piezoelectric disk. In the proposed experiments, RUS is further enhanced by the use of a 3-D laser vibrometer allowing the visualization of most of the modes in the frequency band studied.

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Languages : en
Pages : 4

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The use of mechanical resonances to test properties of materials is perhaps older than the industrial revolution. Early documented cases of British railroad engineers tapping the wheels of a train and using the sound to detect cracks perhaps mark the first real use of resonances to test the integrity of high-performance alloys. Attempts were made in the following years to understand the resonances of solids mathematically, based on the shape and composition. But Nobel Laureate Lord Rayleigh best summarized the state of affairs in 1894, stating {open_quotes}the problem has, for the most part, resisted attack{close_quotes}. More recently, modern computers and electronics have enabled Anderson and co-workers with their work on minerals, and our work at Los Alamos on new materials and manufactured components to advance the use of resonances to a precision non-destructive testing tool that makes anisotropic modulus measurements, defect detection and geometry error detection routine. The result is that resonances can achieve the highest absolute accuracy for any dynamic modulus measurement technique, can be used on the smallest samples, and can also enable detection of errors in certain classes of precision manufactured components faster and more accurately than any other technique.

Author: Frank Arthur Willis
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ISBN:
Category : Resonant ultrasound spectroscopy
Languages : en
Pages : 298

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Author: Abu Rafi Mohammad Iasir
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Category :
Languages : en
Pages : 71

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The purpose of this thesis is to study Resonance Ultrasound Spectroscopy(RUS) and it's potential to evaluate the change in interfacial thermal resistance due to irradiation. Resonant Ultrasound Spectroscopy is conventionally used to determine the material properties of elastic bodies. It is a nondestructive technique that is very capable of extracting the elastic constants for a complete anisotropic material. Finite Element Method(FEM) is used to determine the natural frequency of a hollow cylinder. FEM was used due to the shape of the object. An experimental system was developed to capture the resonant frequencies of a hollow cylinder which is similar to Molybdenum-99 target. After successfully determining the resonance frequencies from the spectra, the frequencies were inverted to the elastic constants using the finite element model. Radiation effects on elastic constants was also studied. An investigation was made to assess the usefulness of RUS in evaluating radiation damage of materials. An experimental study was also completed to analyze the differences in RUS spectra in a contact pressure analysis between two cylinders of Molybdenum-99 target.