Papers by Keyword: Resonant Ultrasound Spectroscopy

Abstract: The transition temperatures of small amounts of eutectic particles contained in free-cutting aluminum alloys (namely AA6262 and AA6023) are investigated in this paper. Detection of the transition temperatures by conventional differential scanning calorimetry (DSC) measurements is difficult because of the small volume fraction (~ 1wt.%) of the eutectic. On the other hand, the melting of the particles induces small changes of elastic moduli of the alloy, which can be sensitively measured by resonant acoustic methods, for example by resonant ultrasound spectroscopy (RUS). It is shown that the phase transitions of the particles correspond to well-detectable changes of the resonant spectrum, which enables a more detailed characterization of the transition process. A significant thermal hysteresis is observed between the cooling and the heating runs, and also the widths of the temperature ranges in which the transitions occur exhibit a strong melting/freezing asymmetry.

Abstract: Resonant ultrasound spectroscopy (RUS) was applied to monitor the micro-cracking process occurring during cooling at polished surfaces of an ultrafine-grained AZ31 magnesium alloy. It was observed that although the net of micro-cracks covered only narrow regions along the edges of the sample, its appearance resulted in a strong increase of the attenuation of the free elastic vibrations, and was, thus, sensitively detectable from the evolution of the RUS resonant spectra with temperature. This approach enabled a reliable determination of the threshold temperature for micro-cracking.

Abstract: The elastic and plastic deformation behaviors of lotus-type porous copper (lotus copper) with cylindrical pores oriented in one direction were investigated using two acoustic methods (resonant ultrasound spectroscopy and acoustic emission method). All the independent components of elastic stiffness were determined by resonant ultrasound spectroscopy combined with electromagnetic acoustic resonance method, which revealed that the Young’s modulus exhibits the anisotropy originating from the anisotropic porous structure and anisotropic matrix texture. The porosity dependence of the anisotropic Young’s modulus can be calculated by the micromechanics modeling based on effective-mean-field theory. The tensile deformation behavior of lotus copper was analyzed by acoustic emission method, which revealed that many burst acoustic emission signals are detected during the tensile deformation. This implies that many cracks are formed during the tensile deformation.

Abstract: In this research, we proposed nondestructive evaluation method of a flaw in an optical glass lens by resonant ultrasound spectroscopy (RUS). An optical glass lens is used for improving signal coupling between fibers, emitters and detectors. The shape of optical glass lens is an aspherical lens with 3mm in length and 6.35 mm in diameter. For nondestructive evaluation of an aspherical lens, we made of the measuring system by RUS. For flaw evaluation by the RUS to verify the data obtained from the experiment, we carried out simulation by explicit finite elements method, and compared the experimental results with simulation results. Also, we compared the resonant frequencies of specimens with some defect with those of acceptable specimens. The histogram drawn from these data and the available resonance mode surveyed were used to classify the acceptable specimens in the plant.

Abstract: Elastic constants of solids were, until recently, evaluated predominantly by pulse-echo ultrasonic methods which are based on measuring the speed of ultrasonic waves propagation in solids. Resonant ultrasound spectroscopy (RUS) is a relatively novel method in which all components of elastic tensor are determined from measured resonance frequencies of a freely vibrating specimen. The RUS technique has been employed in this work to investigate temperature dependence of the elastic properties of the parent austenite phase in CuAlNi shape memory alloy single crystals. This phase exhibits very high elastic anisotropy (anisotropy factor A  12) and softening the shear coefficient C0 upon cooling when approaching the Ms transformation temperature. The complications (need for large number of resonant frequencies) emerging when one tries to determine all elastic constants of highly elastically anisotropic materials by the RUS technique are discussed. It is concluded that the shear coefficients C0 and C44, which are the most important for shape memory alloys, are, nevertheless, determined reliably.

Abstract: RUS−resonant ultrasound spectroscopy is a recent experimental−numerical method for the determination of moduli of elastic materials. Generally, all 21 elastic components of the elastic tensor can be determined by the numerical procedure based on the knowledge of a mechanical spectrum of a specimen. This involves the solution of a demanding inverse problem. Currently, the RUS technology allows the determination of material parameters of composite materials consisting of several layers with different material properties. In the present work, the fixed point iteration method in connection with the finite element method developed earlier is extended to optimize elastic moduli of layered materials. Properties of the fixed point iteration method are tested on a bicrystal specimen.

Abstract: Mechanical properties of two stoichiometric NiAl intermetallic alloys processed by hot hydrostatic extrusion were investigated. The ingots for extrusion process were produced both by casting and by powder metallurgy route in which the self-sustained high-temperature synthesis (SHS) of elemental powders was initialized by the process of extrusion itself. Elastic anisotropy of the obtained products were determined using a resonant ultrasound spectroscopy (RUS) in measurements of the elastic constants. The anisotropy of plastic properties was estimated from uniaxial compression tests on specimens cut off from the material in the main directions of previous deformation. An acoustic emission (AE) method of monitoring of the microcracking process in the material was used for estimation the role of cataclastic mechanism of deformation. The effect of annealing of extruded materials on their plastic behavior was roughly investigated.