Ultrasonic Bulk Waves Research Articles

Ultrasonic wave velocity measurement in small polymeric and cortical bone specimens.

A system was refined for the determination of the bulk ultrasonic wave propagation velocity in small cortical bone specimens. Longitudinal and shear wave propagations were measured using ceramic, piezoelectric 20 and 5 MHz transducers, respectively. Results of the pulse transmission technique were refined via the measurement of the system delay time. The precision and accuracy of the system were quantified using small specimens of polyoxymethylene, polystyrene-butadiene, and high-density polyethylene. These polymeric materials had known acoustic properties, similarity of propagation velocities to cortical bone, and minimal sample inhomogeneity. Dependence of longitudinal and transverse specimen dimensions upon propagation times was quantified. To confirm the consistency of longitudinal wave propagation in small cortical bone specimens (< 1.0 mm), cut-down specimens were prepared from a normal rat femur. Finally, cortical samples were prepared from each of ten normal rat femora, and Young's moduli (Eii), shear moduli (Gij), and Poisson ratios (Vij) were measured. For all specimens (bone, polyoxymethylene, polystyrene-butadiene, and high-density polyethylene), strong linear correlations (R2 > 0.997) were maintained between propagation time and distance throughout the size ranges down to less than 0.4 mm. Results for polyoxymethylene, polystyrene-butadiene, and high-density polyethylene were accurate to within 5 percent of reported literature values. Measurement repeatability (precision) improved with an increase in the wave transmission distance (propagating dimension). No statistically significant effect due to the transverse dimension was detected.

Air-coupled generation and detection of ultrasonic bulk waves in metals using micromachined capacitance transducers

Micromachined capacitance transducers have been used for the first time to generate and detect ultrasonic longitudinal waves in a 5 mm thick aluminum plate in a completely air-coupled mode (i.e. without any contact). The source and receiver were placed on opposite sides of the aluminum plate in a normal-incidence through-thickness arrangement, leaving air gaps between the transducers and sample. The source was excited by a toneburst voltage whose frequency could be swept through the sample's through-thickness longitudinal resonance; whereas the reception circuitry employed a superheterodyned receiver. The measured resonant peak is consistent with that expected for a 5 mm thick aluminum plate, thus confirming generation and detection of bulk longitudinal waves in a metal by a capacitive air-coupled transducer. This work, when combined with previous studies by the author, shows that the entire range of solid materials (i.e. materials with acoustic impedances ranging from that of polymers and paper all the way to that of metals) can now in principle be investigated using micromachined air-coupled capacitance transducers and any of the available ultrasonic wave-modes.

Optimal recovery of the elasticity tensor of general anisotropic materials from ultrasonic velocity data

An ultrasonic wave approach is presented for the optimal identification of the 21 independent elasticity constants of the most general linear homogeneous anisotropic elastic solid from wave speed measurements of obliquely incident ultrasonic bulk waves. Since the symmetry of acquisition planes is not taken into account, this inversion process is generalized to materials that do not possess three mutually orthogonal planes of symmetry. Minimization of an overdetermined system of nonlinear algebraic equations is solved by a constrained optimization method. Various classes of symmetry are considered. Several critical factors (initial guesses, scatter in experimental data) which can influence the accuracy of the elastic property reconstruction algorithm have been investigated by means of numerical examples that simulate in the best way a typical experiment. The sensitivity of the reconstruction algorithm to each identified elasticity constant is detected a posteriori by means of the estimation of a confidence interval associated with each identified constant. The generalized reconstruction method is applied to the experimental data for materials with various symmetry classes.

Focused bulk ultrasonic waves generated by ring-shaped laser illumination and application to flaw detection

Focused bulk ultrasonic waves have been generated in aluminum plates by surface irradiation with ring-shaped laser light. The waves are detected by a piezoelectric transducer. Compression and shear peak amplitudes drop quickly when the detector is moved away from the epicenter. This shows that strong focusing exists at the epicenter as the result of constructive interference of the waves generated by different parts of the ring. The focusing persists when the radius of the laser light is scanned over a large range, indicating that the elastic disturbance concentrates in depth along the ring’s central axis. Numerical simulations are presented for comparison. The ‘‘pencil-like’’ acoustic wave structure is used to observe a sample plate with an artificial flaw. Strong new features including compress-shear mode conversion at the site of the flaw are observed. These features are used to locate the flaw within the sample.

Elastic wave generation by piezoceramic patches

Elastic flexural and longitudinal waves can be generated in structure by using piezoelectric transducers. These waves may be used to obtain fundamental properties of the medium or to locate flaws. Bulk waves can be created in a thin piezoelectric plate by applying an electrical signal to interdigital electrodes deposited on each side of the plate. These transducers can be used to generate ultrasonic bulk waves with a wide range of frequencies and amplitudes controlled by a number of electrodes and a delayed voltage independently applied to each electrode. Numerical results demonstrating the finite element simulation of piezoelectric actuators and sensors in generating and detecting elastic bulk waves are presented. Experimental observations of flexural waves generated hy surface mounted piezoceramic plates are compared with the finite element results. Bulk wave generation and detection using interdigital electrodes are simulated and their potential application as probes in smart structures is discussed.

Determination of interphasial elastic properties in fiber composites from ultrasonic bulk wave velocities : Rokhlin, S.I.; Chu, Y.C. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 1–6 Aug. 1993. Vol. 13B, pp. 1461–1468. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1994) ISBN 0-306-44731-2

Determination of interphasial elastic properties in fiber composites from ultrasonic bulk wave velocities : Rokhlin, S.I.; Chu, Y.C. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 1–6 Aug. 1993. Vol. 13B, pp. 1461–1468. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1994) ISBN 0-306-44731-2

Measurement of elastic constants in composite materials using air-coupled ultrasonic bulk waves

This paper presents numerical simulations and experimental measurements of longitudinal and shear bulk waves in composite materials, generated and detected with an air-coupled ultrasonic system. The transfer function of an anisotropic absorbing layered plate immersed in air is computed with the transfer matrix method, and the waveforms produced by transmission through a plate are simulated from the convolution of a reference waveform and the impulse response of the plate. The calculated waveforms compare well to those recorded experimentally, confirming that the waveforms recorded experimentally have the correct characteristics. It is demonstrated that it is possible to identify longitudinal and shear modes. Results are presented showing how this data may be used to recover the stiffness matrix of composite materials, using the angular variation of velocity of both modes.

Assessment of Damage in Ceramics and Ceramic Matrix Composites Using Ultrasonic Techniques

This paper addresses the application of ultrasonic methods to damage assessment in ceramics and ceramic matrix composites. It focuses on damage caused by thermal shock and oxidation at elevated temperatures. The damage-induced changes in elastic constants and elastic anisotropy are determined by measuring the velocities of ultrasonic waves in different propagation directions within the sample. Thermal shock damage measurement is performed in ceramic samples of reaction bonded silicon nitride (RBSN) and aluminum oxide. Thermal shock treatment from different temperatures up to 1000°C is applied to produce the microcracks. Both surface and bulk ultrasonic wave methods are used to correlate the change of elastic constants to microstructural degradation and to determine the change in elastic anisotropy induced by microcrack damage. Oxidation damage is studied in silicon carbide fiber/reaction bonded silicon nitride matrix (SCS-6/RBSN) composites. The oxidation is done by exposing the samples in a flowing oxygen environment at elevated temperatures, up to 1400°C, for 100 hours. Significant changes of ultrasonic velocities were observed for composites before and after oxidation. The elastic constants of the composites were determined from the measured velocity data. The Young’s modulus in the fiber direction as obtained from ultrasonic measurements decrases significantly at 600°C but retains its original value at temperatures above 1200°C. This agrees well with the results of destructive tests by other authors. The transverse longitudinal and shear moduli obtained from ultrasonic measurements decrease continually until 1200°C. The results of this work show that the damage-induced anisotropy in both ceramics and ceramic matrix composites can be determined successfully by ultrasonic methods. This suggests the possibility of assessing damage severity using ultrasonic techniques.

Ultrasonic texture and stress measurements in anisotropic polycrystalline aggregates : Delsanto, P.P.; Mignogna, R.B.; Clark, A.V. Journal of the Acoustical Society of America, Vol. 87, No. A, pp. 215–224 (Jan. 1990)

A perturbative treatment of ultrasonic Rayleigh wave propagation is applied to investigate the case of an initally deformed metal plate, assumed to be homogeneous and to consist of an orthotropic disribution of cubic crystallites. Time‐of‐flight measurement techniques are proposed for the determination of both stress and texture. An analysis of these experimental results and a comparison with results of both ultrasonic bulk waves and neutron diffraction techniques confirm the reliability of this method. The special case of residual stresses is discussed in detail. Measurements of residual stresses with this technique agree with the results of strain gage measurements.

Optodynamic aspect of a pulsed laser ablation process

A study of a pulsed laser ablation process is presented from a novel, optodynamic aspect. By quantitative analysis of laser-induced bulk ultrasonic and blast waves in the air the ablation dynamics is characterized. In this way the influence of the laser pulse parameters and of the interacting material on the ablation process was assessed. By the analysis of the laser drilling process of thin layered samples the material influence was demonstrated. Besides the ultrasonic evaluation of the laser pulse power density the plasma shielding for 10 ns laser pulses was analyzed by the same method. All measurements were noncontact. Bulk waves in the solid and blast waves in the air were measured simultaneously, an interferometric and a probe beam deflection method were used, respectively.

A study on the influence of fiber-matrix interphase properties on ultrasonic wave behavior using effective elastic property models

In this paper, a three-phase (fiber-interphase-matrix unit cell) micro-mechanics model (Gardner et al. (1993), Comp. Sci. Technol. 46, 307–318) is used to study the influence of fiber-matrix interphase properties on the overall effective elastic constants. Then, the behavior of measurable ultrasonic parameters such as velocities of the three ultrasonic bulk wave modes, and their reflection factor (as a function of wave orientation and frequency) is discussed as a function of interphase properties. Theoretical results are compared with experimental studies on both glass-epoxy and graphite-epoxy composites.

Comparative analysis of through-transmission ultrasonic bulk wave methods for phase velocity measurements in anisotropic materials

In this paper a critical evaluation of ultrasonic bulk wave velocity measurements by the through-transmission and the recently introduced self-reference methods is reported. The major difference in these two techniques is the reference acoustic path: through-water for the through-transmission method and through-sample at normal incidence for the self-reference method. The error introduced by geometrical imperfection of the sample is compared theoretically and experimentally for two methods. Composite materials with different anisotropies are used in the experiment, including ceramic matrix (SiC/Si3N4) and graphite/epoxy composites. Both analytical and experimental studies show that the self-reference method has advantages over the through-transmission method, which is susceptible to geometrical imperfections in the sample. The effect of temperature fluctuation on the accuracy of ultrasonic phase velocity measurements is discussed and different compensation techniques are proposed.

46902 The elastic moduli of a thick composite as measured by ultrasonic bulk wave pulse velocity : Papadakis, E.P.; Patton, T.; Tsai, Y.-M.; Thompson, D.O.; Thompson, R.B. Journal of the Acoustical Society of America, vol. 89, no. 6, pp. 2753–2757 (Jun. 1991)

46902 The elastic moduli of a thick composite as measured by ultrasonic bulk wave pulse velocity : Papadakis, E.P.; Patton, T.; Tsai, Y.-M.; Thompson, D.O.; Thompson, R.B. Journal of the Acoustical Society of America, vol. 89, no. 6, pp. 2753–2757 (Jun. 1991)

Stability of determination of composite moduli from velocity data in planes of symmetry for weak and strong anisotropies

The determination of elastic constants from ultrasonic bulk wave velocity data taken in a plane of symmetry is studied. It is shown that the problem is well-posed, i.e., the solution is unique and stable. The displacement polarization factors are used to define the degree of material anisotropy and represent solutions of the Christoffel equation. Such a representation in a rotated coordinate system helps to derive simple expressions for coefficients describing the sensitivity of ultrasonic waves to different elastic constants. Thus the optimal refraction angles for velocity measurement can be determined simply. The analysis performed shows that the elastic constants reconstructed from velocity data are not affected by the selection of initial guesses used in a nonlinear least-square optimization (the solution is unique). The solution stability is validated by performing reconstruction with different levels of random scatter in the velocity data. The effect of the angle range used for velocity measurements has been analyzed, and it is shown that, depending on the refraction-angle range, reconstruction of the longitudinal elastic constants is dominated either by the quasilongitudinal or by the quasitransverse velocity. The desirable range of refraction angles for determination of elastic constants with high accuracy is determined.

On-line measurement of plastic strain ratio of steel sheet using resonance mode EMAT

We have developed an on-line system for the measurement of plastic strain ratio of steel sheet using a thickness resonance EMAT that measures the thickness resonance frequencies of three different modes of bulk ultrasonic waves. The effective size of the EMAT is small, about 20 mm in diameter. A good correspondence was obtained between the in-plane average Young's modulus measured by this method and the in-plane average plastic strain ratio measured by tensile testing, with a standard deviation smaller than 0.04 in units of plastic strain ratio. The effects of temperature, lift-off, tensile stress, speed of the moving sheet and zinc coats were experimentally and theoretically analyzed. We show that none of them have a sizable effect on the measurement accuracy.

Determination of macro- and micromechanical and interfacial elastic properties of composites from ultrasonic data

A self-reference ultrasonic bulk wave method for nondestructive measurement of elastic properties of ceramic matrix composites has been developed. The method has the advantage of minimizing the effect of geometrical imperfection of the sample. The experiment has been done on silicon carbide (SiC) fiber-reinforced reaction-bonded silicon nitride (Si3N4) matrix composites. The composite elastic constants are extracted from the experimental phase velocities using a nonlinear optimization procedure to find the best fit between experimental data and the solutions of the Christoffel equation. The effect of individual constituents on the overall composite properties has been investigated. The effects of porosity on the matrix properties and water saturation of pores on the immersion ultrasonic measurements are taken into account using a micromechanical model for two-phase particulate composites. This model is validated by experimental data. A microstructural model for analysis of elastic properties of ceramic matrix composites and their interfaces from experimental data is introduced. The fiber and the interface are modeled by effective fibers with anisotropic properties and a perfect bond between fiber and matrix. The properties of the effective fibers are extracted from the measured composite elastic moduli using a nonlinear optimization procedure. Shear and longitudinal elastic moduli of 3-μm-thick carbon-rich coatings are determined using measured effective and estimated actual elastic properties of the fibers.

Thermal Shock Damage Assessment in Ceramics Using Ultrasonic Waves

Structural ceramics are susceptible to microcrack damage by thermal shock. There is a critical temperature for thermal shock damage initiation with damage severity increasing at greater shock temperatures. In this work the applicability of an ultrasonic method to determine the critical temperature and the accumulated damage is demonstrated in alumina. Information is obtained via velocity and attenuation measurements using surface and obliquely incident bulk ultrasonic waves. The elastic anisotropy effect due to preferred crack orientation has been estimated. The critical temperature for the alumina is about 200°C. The damage increases steeply from 200° to 400°C and grows significantly above 400°C. Changes of up to 17% from the original values in the effective shear moduli and up to 45% in the longitudinal effective modulus in the direction transverse to crack orientation are measured at high thermal shock temperatures.

ÉVALUATION DE L'ADHÉRENCE PAR ULTRASONS HAUTE-FRÉQUENCE

Numerous studies have already been performed for estimating the adhesion between two materials using ultrasound. The results obtained, mainly with Lamb Waves, don't lead to a quantitative evaluation of adhesion. We investigated the use of high frequency, 50 to 500 MHz, bulk (longitudinal and shear) ultrasonic waves for evaluating the adhesion from the reflection or transmission coefficient at an interface

The elastic moduli of a thick composite as measured by ultrasonic bulk wave pulse velocity

One thick filament-wound composite in the form of a large thick-walled cylinder with locally orthorhombic symmetry has been measured by ultrasonic velocity to calculate its elastic moduli. The basic assumption was that small sections of the composite could be treated as a homogeneous body analogous to a crystal for ultrasonic propagation. The experimental work and the results as best expressing homogeneous body theory are presented. Because of the high anisotropy with the normal to the layers (the three-direction) much different from the axial and hoop directions, it was necessary to calculate slowness surfaces with approximate values of c13 and c23 in order to find the directions of the Poynting vectors to use in making actual measurements on c12 and c13.

Ultrasonic texture and stress measurements in anisotropic polycrystalline aggregates

A perturbative treatment of ultrasonic Rayleigh wave propagation is applied to investigate the case of an initally deformed metal plate, assumed to be homogeneous and to consist of an orthotropic disribution of cubic crystallites. Time-of-flight measurement techniques are proposed for the determination of both stress and texture. An analysis of these experimental results and a comparison with results of both ultrasonic bulk waves and neutron diffraction techniques confirm the reliability of this method. The special case of residual stresses is discussed in detail. Measurements of residual stresses with this technique agree with the results of strain gage measurements.