Wave Speed Measurements Research Articles

Shock-loading response of 6061- T6 aluminum metal-matrix composites

The purpose of this research was to systematically study the influence of peak-shock pressure and second-phase reinforcement on the structure/property response of shock-loaded 6061-T6 Al-alumina composites. The reload stress-strain response of monolithic 6061-T6 Al, used as a baseline for comparison, showed no increased shock hardening compared to the unshocked material deformed to an equivalent strain. The reload stress-strain response of the shock-loaded 6061-T6 Al-alumina composites exhibited a lower reload yield strength than the flow stress of the starting composites. The degree of strength loss was found to increase with increasing shock pressure. Wavespeed measurements of shock-prestrained specimens showed no degradation compared to unshocked specimens, indicating that particle cracking had not occurred under shock. This result was supported by optical metallography, which did not reveal cracked particles or particle decohesion in the shock-prestrained samples. The reload stress-strain response of the shock-prestrained composites, after resolutionizing and T6 reaging, showed that the composites recovered their full as-received preshock stress-strain responses. This result supports the finding that degradation in reload strength was attributable to matrix microstructural changes resulting from the shock. Transmission electron microscopy (TEM) examination of the shock-loaded microstructures revealed that the matrix regions adjacent to the particle/matrix interface had undergone significant recovery and partial recrystallization resulting from the shock. This type of near-interface substructure is in stark contrast to the heavily dislocated near-interface dislocation substructure of the as-received composites. The loss of dislocation density(i.e., strain hardening) in the near-interface matrix region, resulting from the shock, highlights the importance of the thermally introduced dislocation substructure changes in establishing the strength of metal-matrix composites (MMCs).

Ultrasonic technique to measure stiffness coefficients of CMC and its implications on characterizing material degradation

The main objectives of this research are to characterize the fiber content of composite materials using nondestructive methods, to characterize fiber, matrix and fiber-matrix interface degradation in a quantitative manner and to predict the elastic behavior of the composite material using ultrasonic techniques. We can achieve the above objectives if we can experimentally compute the stiffness matrix that can be derived by either destructive or nondestructive methods. We focus on nondestructive methods to generate the stiffness matrix of ceramic matrix composites (CMC) using ultrasonic techniques. The use of ultrasonic waves in measurement of the dynamic elastic moduli of solids is well known (Truell et al. (1969). Ultrasonic Methods in Solid State Physics, Academic Press). If the density and elastic anisotropy of a solid are specified then the elastic moduli can be deduced from wave speed measurements of shear and longitudinal waves propagating in particular directions in the solid. The relations between wave speed and moduli follow from the theory of small amplitude elastic wave propagating in an anisotropic solid (Musgrave (1970). Crystal Acoustics, Holden-Day). In this paper, we will discuss the experiments conducted on three CMC (CAS-Nicalon) unidirectional blocks with varying fiber fractions estimated at 31, 42 and 51%, using ultrasonic longitudinal, transverse and surface acoustic wave (SAW) velocities. Techniques to improve and automate data acquisition are discussed along with the experimental results.

An Experimental Investigation of Damage Evolution in a Ceramic Matrix Composite

The mechanical behavior of a glass-ceramic matrix composite, SiC/CAS (calcium aluminosilicate reinforced with unidirectional SiC fibers), is studied. Results based on uniaxial tension experiments are presented for specimens with fibers aligned in the loading direction. Axial and transverse strain gages on all four gage section surfaces and in situ acoustic emission and ultrasonic wave speed measurements were used to monitor the evolution of damage. All measurements were made with high-resolution, continuous data acquisition. Post-test optical and scanning electron microscopy was also used to identify the various micromechanisms of damage. The experimental results demonstrate the existence of “zones of deformation” which are associated with the onset of different damage mechanisms. It is shown that the observed stress-strain behavior can be explained in terms of the material properties of the matrix and the fiber, the material processing, and the postulated zones of deformation.

Ultrasonic measurements in air or water saturated porous media

Low-frequency (20 kHz–180 kHz) ultrasonic measurements have been performed in numerous air-saturated acoustic materials, i.e., various foams and felts. By using a standard pulse-echo technique, very precise wave-speed measurements were achieved with either a cross-correlation procedure or by using the Hilbert transform of the transfer function between a reference signal (with no sample) and the signal transmitted through the sample. The amplitude measurements were done in the Fourier domain via the cross power. The signal processing routines were implemented in the LabVIEW 2.0 environment. Some significant physical properties (e.g., tortuosity) related to the propagation of acoustic waves in porous media [e.g., J.-F. Allard, PropagationofSoundinPorousMedia (Elsevier, New York, (1993)] were obtained. Preliminary results made at 500 kHz, with the aim of measuring the viscous as well as thermal characteristic lengths, on water-saturated sandstone specimens will also be reported.

Evaluation of tortuosity in acoustic porous materials saturated by air

Tortuosity is an important parameter for the prediction of the acoustical properties of porous sound absorbing materials. The evaluation of tortuosity by resistivity measurements is now used in several laboratories, although this method presents several drawbacks. In particular, the complete saturation by a conducting fluid of a porous foam having a high flow resistivity is difficult to obtain without partially damaging the structure of the cells. A simple technique based on ultrasonic wavespeed measurements in a material saturated by air is described. This method has been used previously only for water or superfluid helium saturated materials.

44144 Optimized determination of elastic constants of anisotropic solids from wavespeed measurements : Castagnede, B.; Sachse, W. Proceedings of the 15th Annual Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (USA), 31 Jul. – 5 Aug. 1988. vol. 8B, pp. 1855–1862. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1989). ISBN 0-306-43209-9

44144 Optimized determination of elastic constants of anisotropic solids from wavespeed measurements : Castagnede, B.; Sachse, W. Proceedings of the 15th Annual Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (USA), 31 Jul. – 5 Aug. 1988. vol. 8B, pp. 1855–1862. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1989). ISBN 0-306-43209-9

43874 Optimal determination of the elastic constants of composite materials from ultrasonic wave-speed measurements : Castagnede, B.; Jenkins, J.T.; Sachse, W.; Baste, S. Journal of Applied Physics, vol. 67, no. 6, pp. 2753–2761 (15 Mar. 1990)

43874 Optimal determination of the elastic constants of composite materials from ultrasonic wave-speed measurements : Castagnede, B.; Jenkins, J.T.; Sachse, W.; Baste, S. Journal of Applied Physics, vol. 67, no. 6, pp. 2753–2761 (15 Mar. 1990)

High-resolution radar on Ice Stream B2, Antarctica: measurements of electromagnetic wave speed in firn and strain history from buried crevasses

Two types of experiments were performed near Upstream B Camp on Ice Stream B2 using a high-resolution ground-penetrating radar system. In the first type of experiment, tracking a metal drill tip through the upper 85 m of the ice column indicated an approximately linear decrease of wave speed with depth down to 50 m, with a constant speed of 170 ± 4 m µs−1 below. We believe the (unexpected) linearity may have been caused by one or more buried crevasses. In the second experiment, a survey of a 250 km2 grid showed a population of buried crevasses at about 30 m depth that have an estimated burial age of 210 ± 25 years, which is taken to indicate that this ice has been exhibiting streaming behavior for at least that length of time. One 3 km segment along the edge of the survey area nearest the center of the stream showed virtually flat, undisrupted stratigraphy down to the maximum depth of our measurements. The fact that this ice was accelerated from near-zero speed to its present 440 m a−1 without cracking or folding suggests that this ice may have been incorporated into the ice stream as a solid block.

High-resolution radar on Ice Stream B2, Antarctica: measurements of electromagnetic wave speed in firn and strain history from buried crevasses

Two types of experiments were performed near Upstream B Camp on Ice Stream B2 using a high-resolution ground-penetrating radar system. In the first type of experiment, tracking a metal drill tip through the upper 85 m of the ice column indicated an approximately linear decrease of wave speed with depth down to 50 m, with a constant speed of 170 ± 4 m µs−1 below. We believe the (unexpected) linearity may have been caused by one or more buried crevasses. In the second experiment, a survey of a 250 km2 grid showed a population of buried crevasses at about 30 m depth that have an estimated burial age of 210 ± 25 years, which is taken to indicate that this ice has been exhibiting streaming behavior for at least that length of time. One 3 km segment along the edge of the survey area nearest the center of the stream showed virtually flat, undisrupted stratigraphy down to the maximum depth of our measurements. The fact that this ice was accelerated from near-zero speed to its present 440 m a−1 without cracking or folding suggests that this ice may have been incorporated into the ice stream as a solid block.

High-resolution radar on Ice Stream B2, Antarctica: measurements of electromagnetic wave speed in firn and strain history from buried crevasses

Two types of experiments were performed near Upstream B Camp on Ice Stream B2 using a high-resolution ground-penetrating radar system. In the first type of experiment, tracking a metal drill tip through the upper 85 m of the ice column indicated an approximately linear decrease of wave speed with depth down to 50 m, with a constant speed of 170 ± 4 m µs−1 below. We believe the (unexpected) linearity may have been caused by one or more buried crevasses. In the second experiment, a survey of a 250 km2 grid showed a population of buried crevasses at about 30 m depth that have an estimated burial age of 210 ± 25 years, which is taken to indicate that this ice has been exhibiting streaming behavior for at least that length of time. One 3 km segment along the edge of the survey area nearest the center of the stream showed virtually flat, undisrupted stratigraphy down to the maximum depth of our measurements. The fact that this ice was accelerated from near-zero speed to its present 440 m a−1 without cracking or folding suggests that this ice may have been incorporated into the ice stream as a solid block.

Propagation of leaky plate waves in fluid-loaded composite laminates

An analytical model for the reflection coefficient of a multi-directional composite laminate immersed in fluid is proposed. The model is based on the use of effective laminate properties. The predicted amplitudes of reflected beams compared favorably with the experimental values. The leaky plate wave speeds were measured in various directions of the unidirectional laminate and three other laminates (quasi-isotropic, angle-ply, and cross-ply) using nonspecular ultrasonic reflection. The measured wave speeds agreed well with the predicted ones considering the heterogeneity of the composites used.

Effective elastic moduli and characterization of a particulate metal-matrix composite with damaged particles

A brief summary of analytical models is given for estimating effective elastic moduli of discontinously reinforced metal-matrix composites (DMMCs) with damaged particles (either complete voids as shattered particles, or debonded particles, or penny-shaped cracks). The analytical results are then compared with elastic moduli determined from non-destructive ultrasonic wave-speed measurements of SiC-particle-reinforced titanium-matrix composites produced by shock-wave consolidation. For the shock-consilidated TiSiC metal-matrix composite compacts, the overall particle damage mode is found to be similar to debonded particles and the effective volume fraction of damaged particles is determined to be 0·39 on the basis of the data for both Young's and bulk moduli. Ultrasonic wave-speed measurements combined with analytical and/or numerical results on overall elastic properties (Young's, bulk and shear moduli, and Poisson's ratio) could be a useful tool in assessing the damage of particles in DMMCs.

Détermination des temps d'arrivée de fronts d'onde acoustiques divergents dans une lame anisotrope

The present work is an attempt to extend to the acoustics of anisotropic media the basic principles of optics. The acoustical case is much more intricate because of the possibility of existence of the cuspidal caustics. Firstly, one discusses the mathematical transformation between phase and group wavespeeds. Then, the problem of the reflection of a divergent acoustical ray onto an interface is studied with the help of Huyghens construction. A generalization of the classical refraction law is obtained. Such a result can also be derived from Fermat principle. It is possible to numerically verify the absence of precursor on the converted mode, due to the non-existence of caustics after reflection. A discussion on the so-called Cagniard-de-Hoop contours is introduced, as well as a numerical procedure to compute the direction of the reflected ray. Different cases, depending on the source dimension (point-like or line) and on the orientation cut of the anisotropic solid, are discussed. The extension of the study to several reflections is proposed. Special attention is also devoted to the analysis of the head wavefront reflection. Last, some experimental results dealing with the measurements of group wavespeeds in a transversely isotropic composite material are described. The present study will be followed by the computation of the Green functions and the comparison with experimental displacement fields for various anisotropic solids

Independent confirmation that delayed die swell is a hyperbolic transition

We measured shear wave speeds in the same aqueous Xathan solutions used to study delayed die swell by Allain et al. (Eur. J. Mech. A/Fluids, 12 (1993) 175-186). They reported delayed die swell for solutions of 500, 1000, 2000 and 4000 ppm Xanthan in water when the shear rate, 8 U/d, was above a critical value 8 U c/ d, where U is the mean velocity through a round pipe of diameter d = 0.6 mm and U c is a critical value. Their photographs of delayed die swell are exactly like those reported by Joseph et al. (J. Non-Newtonian Fluid Mech., 24 (1987) 31-65) for 17 different polymer solutions, by Joseph (Fluid Dynamics of Viscoelastic Liquids, Springer-Verlag, New York, 1990) for 18 and by Hu et al. (J. Non-Newtonian Fluid Mech., 35 (1990) 287-307) for Ml. Allain et al. sent us samples of the four solutions, prepared by them, and we measured wave speeds on our meter. As in all the earlier experiments, the delay occurs when the centerline velocity in the pipe U = 2 U is greater than the wave speed C, and after a distance L the swell is complete and the mean velocity is less than C. This adds four more cases, 23 in all, to those for which the delay can be correlated with the wave speed measured on our meter. So far 23, and only 23, cases have been studied and they are all consistent with calculations from theory giving rise to hyperbolicity and change of type.

In vivo measurement of laryngeal mucosal wave speed in humans

Measurement of laryngeal mucosal wave speed is potentially important for understanding laryngeal vibration and for guiding phonosurgery. However, measurement of wave speed requires knowledge of distance or phase angle on the vocal folds, and has not been possible in awake patients. A new method permitting such measurements in an office setting is described. This method can be applied using either a calibrated fiberoptic nasopharyngoscope or a calibrated laryngoscope to measure absolute distances in the larynx accurately, reliably, and noninvasively. Wave speeds were measured in one normal male speaker at varying levels of F0 and intensity. Across conditions, measured mucosal wave speed ranged from 0.29 to 1.18 m/s. Wave speeds varied significantly with vocal intensity (r=0.72), but not with F0 (r=0.14). Theoretical implications of these findings will be discussed, along with clinical applications of the new techniques.

Shear acoustic properties of soft biological tissues in medical diagnostics

This report is a summary of the studies of shear acoustic properties of soft biological tissues performed by the author and his co-workers in the period from 1966 to the present. A number of techniques for measuring shear elastic moduli of soft tissue in a range of frequencies are described. Methods are considered based on the measurements of acoustic impedance, the shear and surface wave speeds, as well as of static moduli. Results of invitro studies of animal and human tissues and of such model systems as various gels and rubbers are presented. Invivo studies were made on superficial tissues such as the skin and the nearest underlying tissues. It has been shown that surface acoustic waves can be successfully used in the diagnosis of various dermatitis and skin cancer as well as for monitoring of the efficacy of treatment. In response to the needs of the newly developing technique of ultrasonic elasticity imaging of the breast, systematic studies involving 162 excised samples of glandular, fatty, cancerous, and fibroadenoma tissues were performed and the ranges of variation of shear moduli were evaluated. a)Permanent address: Inst. of Theoret. and Exp. Biophys., Russian Acad. Sci., Pushchino 142292, Russia.

On the determination of sound speeds in cubic crystals and isotropic media using a broadband ultrasonic point-source/point-receiver method

This paper describes methods for determining the speeds of elastic waves propagating in cubic single crystals using a broadband point-source and point-receiver, i.e., PS/PR, technique in which transient ultrasonic pulses are simultaneously propagated over a broad angular range of directions in a specimen. Emphasis is given to determination of all three wave speeds from one detected waveform resulting from a single excitation pulse. First described is the determination of both longitudinal and shear wave speeds in an isotropic solid from the waveform detected by an arbitrarily located sensor. Then, measurements made in various directions in 〈100〉-, 〈110〉-, and 〈111〉-oriented silicon single crystal plates are analyzed. It is found that one obtains the most accurate determination of the three wave speeds from a single waveform detected by the sensors located in a {101}-type direction in both 〈100〉- and 〈110〉-oriented crystal specimens. It is found that a pointlike capacitive displacement sensor generally yields better results for the wave-speed measurements than a pointlike piezoelectric transducer.

電波空間フィルタによる電波空間パターンの低域成分の除去と速さ計測

電波空間フィルタによる電波空間パターンの低域成分の除去と速さ計測

Experimental examination of growing and newly submerged sea ice including acoustic probing of the skeletal layer

Results of an in-situ experiment to examine acoustic parameters and scattering properties of growing and newly submerged arctic sea ice are presented. The primary emphasis is on the acoustic properties of highly porous sea ice. High resolution (to about 1 cm) vertical profiles of the longitudinal wave speed in growing and submerged sea ice are derived from the experimental data. The results indicate a skeletal layer about 3 cm thick at the bottom of the growing ice. The time dependence of the vertical sound-speed profile in a submerged block reveals a long time scale process of up to 80 h and a short process of a few hours. The former process is block warming, the latter is thought to be due to the disturbance of the hydrostatic equilibrium as the ice is submerged. Concurrently with the wave speed measurements, scattering from the underside of the ice was measured at several frequencies. A comparison with predictions based on the sound-speed data demonstrate the ability to predict normal incidence reflectivity from sound-speed profiles as well as the viability of using scattering data in inversions to obtain sound-speed profiles. The data were also used to calculate the absorption of a longitudinal wave propagating vertically. The peak absorption rate in the skeletal layer was between 2 and 5 dB/cm at 92 kHz. The temperature dependence of the absorption seen in the submerged ice suggests that the McCammon–McDaniel equation is useful away from the skeletal layer. [Work supported by the Office of Naval Research (N00014-91-J-1647).]

Experimental examination of growing and newly submerged sea ice including acoustic probing of the skeletal layer

Results of an in-situ experiment to examine acoustic parameters and scattering properties of growing and newly submerged arctic sea ice are presented. The primary emphasis is on the acoustic properties of highly porous sea ice. High-resolution (to about 1 cm) vertical profiles of the longitudinal wave speed in growing and submerged sea ice are derived from the experimental data. The results indicate a skeletal layer about 3 cm thick at the bottom of the growing ice. The time dependence of vertical sound-speed profiles in a submerged ice block reveals a long time scale process of up to 80 h and a short process of a few hours. The former process is the warming of the block; the latter is thought to be due to the disturbance of hydrostatic equilibrium as the ice is submerged. Concurrently with the wave-speed measurements, scattering from the undersurface of the ice was measured at several frequencies. A comparison with predictions based on the sound-speed data demonstrates the ability to predict normal incidence ice reflectivity from sound-speed profiles as well as the viability of using scattering data in inversions to obtain sound-speed profiles. Absorption of a longitudinal wave propagating vertically in ice was also measured. The peak absorption rate found in the skeletal layer was between 2 and 5 dB/cm at 92 kHz. The temperature dependence of absorption seen in the submerged ice suggests that the McCammon–McDaniel equation (∼T−2/3) is useful away from the skeletal layer. The measurements of ice temperature as a function of time and depth allow a calculation of the thermal diffusivity of the upper region of growing sea ice (0.0080 cm2/s) and an ‘‘effective’’ thermal diffusivity of the submerged ice block (about 0.0015 cm2/s ). Measurements of salinity profiles in the ice, along with the temperature profiles, are used to calculate porosity, which is then used in models of the longitudinal wave speed as a function of porosity. A comparison between models and experiment is employed that suggests a possible mechanism for the increased speed seen experimentally in the bottom portion of the ice after submergence.