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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Implications of Sound Velocities of Natural Topaz on the Seismic L–Discontinuity

Compressional and shear wave velocities of topaz have been measured by ultrasonic interferometry in a multi-anvil apparatus up to 13 GPa at room temperature. By fitting the measured velocities under pressure to finite strain equations, the elastic moduli of topaz and their pressure derivatives were obtained, yielding K S0 = 165.5 (25) GPa, K S ' = 2.9 (1), G 0 = 116.5 (17) GPa, and G' = 1.0 (1). Modeling of the velocity profiles of subducted sediments suggests that at 8 GPa (~240 km depth) the P- and S- wave velocities of the subducted sediments exhibit a first order increase of 10% and 11%, respectively. Furthermore, the comparison between seismic observations and velocity contrasts of sediment + MORB model at 240 km shows dehydration of a 1.5–3.9 km thick sediment layer can potentially contribute to the seismically observed Lehmann discontinuity in Tonga, Japan, Philippine Sea, South America, Indonesia, and South Shetland subduction zones.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Acousto-ultrasonics

The theoretical development, methodology, and potential applications of acousto-ultrasonic nondestructive testing are set forth in an overview to assess the effectiveness of the technique. Stochastic wave propagation is utilized to isolate and describe defects in fiber-reinforced composites, particularly emphasizing the integrated effects of diffuse populations of subcritical flaws. The generation and nature of acousto-ultrasonic signals are described in detail, and stress-wave factor analysis of the signals is discussed. Applications of acousto-ultrasonics are listed including the prediction of failure sites, assessing fatique and impact damage, calculating ultimate tensile strength, and determining interlaminar bond strength. The method can identify subtle but important variations in fiber-reinforced composites, and development of the related instrumentation technology is emphasized.

Vary, Alex↗
NASA NTRS1991

Application of Guided Acoustic Waves to Delamination Detection

The occurrence of delamination in laminate structures is one of the major reliability concerns for using these materials. There are continuing needs for developing delamination inspection techniques to measure specimens of various material structure as well as to accommodate different test environments. In the case of disbond-detection in the skin of an aircraft, for some practical reasons, an efficient technique should be capable of inspecting a large surface area in a reasonably short amount of time and with a high degree of accuracy. While most existing measurements can provide satisfactory accuracy, the required high inspection rate may not be met. Thus, for assessment of large surface area with an ultrasonic technique, our approach is to generate sound waves of particular modes, which are capable of propagating in a relatively extended area on the surface of a plate and at meantime interrogating the structural integrity of the plate. It is well known in waveguide theory [1-3] that certain modes of sound waves are capable of propagating a relatively long distance in a material of plate configuration, and that their propagation properties are determined in part by the product of sound frequency and plate thickness. Recently, it was found experimentally that, with this thickness dependence, certain modes of these plate waves provided a different approach to probe the flaws in a laminate structure, and with potential application to the large area disbond and crack inspection.

Sun, Keun J.↗
NASA NTRS1999

An Ultrasonic Technique to Determine the Residual Strength of Adhesive Bonds

In this work, ultrasonic techniques to nondestructively evaluate adhesive bond degradation have been studied. The key to the present approach is the introduction of an external factor which pulls the adhesive bond in the nonlinear range, simultaneously with the application of an ultrasonic technique. With the aid of an external static tensile loading, a superimposed longitudinal wave has.been used to obtain the slopes of the stress-strain curve of an adhesive bond at a series of load levels. The critical load, at which a reduction of the slope is detected by the superimposed longitudinal wave, is an indication of the onset of nonlinear behavior of the adhesive bond, and therefore of bond degradation. This approach has been applied to the detection of adhesive bond degradation induced by cyclic fatigue loading. Analogously to the longitudinal wave case, a superimposed shear wave has been used to obtain the effective shear modulus of adhesive layers at different shear load levels. The onset of the nonlinear behavior of an adhesive bond under shear loading has been detected by the use of a superimposed shear wave. Experiments show that a longitudinal wave can also detect the nonlinear behavior when an adhesive bond is subjected to shear loading. An optimal combination of ultrasonic testing and mechanical loading methods for the detection of degradation related nonlinear behavior of adhesive bonds has been discussed. For the purpose of a practical application, an ultrasonic technique that uses a temperature increase as an alternative to static loading has also been investigated. A general strain-temperature correspondence principle that relates a mechanical strain to a temperature has been presented. Explicit strain-temperature correspondence relations for both the tension and shear cases have been derived. An important parameter which quantifies the relation between the wave velocity and temperature has been defined. This parameter, which is indicative of adhesive bond nonlinearity and which can be conveniently obtained by an ultrasonic measurement, has been used as an indication of adhesive bond degradation. Experimental results have shown that the temperature increase method is a convenient and productive alternative to static loading. A technique which uses the reflected waveform data to obtain the fundamental ultrasonic parameters (transit time, reflection coefficient and attenuation coefficient) of an adhesive bond has also been presented.

Achenbach, J. D.↗
NASA NTRS1991

Rapidly quantifying the relative distention of a human bladder

A device and method was developed to rapidly quantify the relative distention of the bladder of a human subject. An ultrasonic transducer is positioned on the human subject near the bladder. A microprocessor controlled pulser excites the transducer by sending an acoustic wave into the human subject. This wave interacts with the bladder walls and is reflected back to the ultrasonic transducer where it is received, amplified, and processed by the receiver. The resulting signal is digitized by an analog to digital converter, controlled by the microprocessor again, and is stored in data memory. The software in the microprocessor determines the relative distention of the bladder as a function of the propagated ultrasonic energy. Based on programmed scientific measurements and the human subject's past history as contained in program memory, the microprocessor sends out a signal to turn on any or all of the available alarms. The alarm system includes and audible alarm, the visible alarm, the tactile alarm, and the remote wireless alarm.

Companion, John A.↗
NASA NTRS1980

Concepts and techniques for ultrasonic evaluation of material mechanical properties

Ultrasonic methods that can be used for material strength are reviewed. Emergency technology involving advanced ultrasonic techniques and associated measurements is described. It is shown that ultrasonic NDE is particularly useful in this area because it involves mechanical elastic waves that are strongly modulated by morphological factors that govern mechanical strength and also dynamic failure modes. These aspects of ultrasonic NDE are described in conjunction with advanced approaches and theoretical concepts for signal acquisition and analysis for materials characterization. It is emphasized that the technology is in its infancy and that much effort is still required before the techniques and concepts can be transferred from laboratory to field conditions.

Vary, A.↗
NASA NTRS1992

Film condensation in a horizontal rectangular duct

Condensation heat transfer in an annular flow regime with and without interfacial waves was experimentally investigated. The study included measurements of heat transfer rate with condensation of vapor flowing inside a horizontal rectangular duct and experiments on the initiation of interfacial waves in condensation, and adiabatic air-liquid flow. An analytical model for the condensation was developed to predict condensate film thickness and heat transfer coefficients. Some conclusions drawn from the study are that the condensate film thickness was very thin (less than 0.6 mm). The average heat transfer coefficient increased with increasing the inlet vapor velocity. The local heat transfer coefficient decreased with the axial distance of the condensing surface, with the largest change at the leading edge of the test section. The interfacial shear stress, which consisted of the momentum shear stress and the adiabatic shear stress, appeared to have a significant effect on the heat transfer coefficients. In the experiment, the condensate flow along the condensing surface experienced a smooth flow, a two-dimensional wavy flow, and a three-dimensional wavy flow. In the condensation experiment, the local wave length decreased with the axial distance of the condensing surface and the average wave length decreased with increasing inlet vapor velocity, while the wave speed increased with increasing vapor velocity. The heat transfer measurements are reliable. And, the ultrasonic technique was effective for measuring the condensate film thickness when the surface was smooth or had waves of small amplitude.

Lu, Qing↗
NASA NTRS1978

Use of an ultrasonic-acoustic technique for nondestructive evaluation of fiber composite strength

Details of the method used to measure the stress wave factor are described. Frequency spectra of the stress waves are analyzed in order to clarify the nature of the wave phenomena involved. The stress wave factor was measured with simple contact probes requiring only one-side access to a part. This is beneficial in nondestructive evaluations because the waves can run parallel to fiber directions and thus measure material properties in directions assumed by actual loads. The technique can be applied where conventional through transmission techniques are impractical or where more quantitative data are required. The stress wave factor was measured for a series of graphite/polyimide composite panels, and results obtained are compared with through transmission immersion ultrasonic scans.

Vary, A.↗
NASA NTRS1991

Development of an optical fiber interferometer for detection of surface flaws in aluminum

The main objective was to demonstrate the potential of using an optical fiber interferometer (OFI) to detect surface flaws in aluminum samples. Standard ultrasonic excitation was used to generate Rayleigh surface waves. After the waves interacted with a defect, the modified responses were detected using the OFI and the results were analyzed for time-of-flight and frequency content to predict the size and location of the flaws.

Gilbert, John A.↗
NASA NTRS1998

Noncontact Determination of Antisymmetric Plate Wave Velocity in Ceramic Matrix Composites

High-temperature materials are of increasing importance in the development of more efficient engines and components for the aeronautics industry. In particular, ceramic matrix composite (CMC) and metal matrix composite (MMC) structures are under active development for these applications. The acousto-ultrasonic (AU) method has been shown to be useful for assessing mechanical properties in composite structures. In particular, plate wave analysis can characterize composites in terms of their stiffness moduli. It is desirable to monitor changes in mechanical properties that occur during thermomechanical testing and to monitor the health of components whose geometry or position make them hard to reach with conventional ultrasonic probes. In such applications, it would be useful to apply AU without coupling directly to the test surface. For a number of years, lasers have been under investigation as remote ultrasonic input sources and ultrasound detectors. The use of an ultrasonic transducer coupled through an air gap has also been under study. So far at the NASA Lewis Research Center, we have been more successful in using lasers as ultrasonic sources than as output devices. On the other hand, we have been more successful in using an air-coupled piezoelectric transducer as an output device than as an input device. For this reason, we studied the laser in/air-coupled-transducer out combination-using a pulsed NdYAG laser as the ultrasonic source and an air-coupled-transducer as the detector. The present work is focused on one of the AU parameters of interest, the ultrasonic velocity of the antisymmetric plate-wave mode. This easily identified antisymmetric pulse can be used to determine shear and flexure modulus. It was chosen for this initial work because the pulse arrival times are likely to be the most precise. The following schematic illustrates our experimental arrangement for using laser in/air-transducer out on SiC/SiC composite tensile specimens. The NdYAG pulse was directed downward by a 90 infrared prism to the top of the specimen, but at the edge of one end. An energy sensor measured a single pulse at 13 millijoules (mJ) before it passed through the prism, which attenuated 15 percent of its energy. It also provided an output trigger for the waveform time-delay synthesizer.

Kautz, Harold E.↗
NASA NTRS1979

Effects of material inhomogeneities on ultrasonic measurements - The problem and a solution

Most ultrasonic measurements of materials involve the generation of an acoustic wave and the propagation of that wave from a transducer through a coupling medium to a specimen under test. After interacting with the specimen, the wave propagates through the coupling medium to a receiving transducer and is converted to an electrical signal. The information presented to the observer by the electrical signal depends on each element of the system. In this paper, the role that the receiving transducer plays in ultrasonic measurements is examined. The phase-sensitive nature of conventional receiving transducers has, for the most part, been neglected in nondestructive evaluations. This is shown to lead to significant data misinterpretation. A new acoustoelectric transducer (AET) has been developed which is phase insensitive. Comparative data obtained with both conventional and AET transducers are presented and discussed. The AET is shown to produce more accurate measurements for the cases investigated.

Heyman, J. S.↗
NASA NTRS1985

Application of homomorphic signal processing to stress wave factor analysis

The stress wave factor (SWF) signal, which is the output of an ultrasonic testing system where the transmitting and receiving transducers are coupled to the same face of the test structure, is analyzed in the frequency domain. The SWF signal generated in an isotropic elastic plate is modelled as the superposition of successive reflections. The reflection which is generated by the stress waves which travel p times as a longitudinal (P) wave and s times as a shear (S) wave through the plate while reflecting back and forth between the bottom and top faces of the plate is designated as the reflection with p, s. Short-time portions of the SWF signal are considered for obtaining spectral information on individual reflections. If the significant reflections are not overlapped, the short-time Fourier analysis is used. A summary of the elevant points of homomorphic signal processing, which is also called cepstrum analysis, is given. Homomorphic signal processing is applied to short-time SWF signals to obtain estimates of the log spectra of individual reflections for cases in which the reflections are overlapped. Two typical SWF signals generated in aluminum plates (overlapping and non-overlapping reflections) are analyzed.

Karagulle, H.↗
NASA NTRS1985

Application of homomorphic signal processing to stress wave factor analysis

The stress wave factor (SWF) signal, which is the output of an ultrasonic testing system where the transmitting and receiving transducers are coupled to the same face of the test structure, is analyzed in the frequency domain. The SWF signal generated in an isotropic elastic plate is modelled as the superposition of successive reflections. The reflection which is generated by the stress waves which travel P times as a longitudinal (P) wave and s times as a shear (S) wave through the plate while reflecting back and forth between the bottom and top faces of the plate is designated as the reflection with P, s. Short-time portions of the SWF signal are considered for obtaining spectral information on individual reflections. If the significant reflections are not overlapped, the short-time Fourier analysis is used. A summary of the elevant points of homomorphic signal processing, which is also called cepstrum analysis, is given. Homomorphic signal processing is applied to short-time SWF signals to obtain estimates of the log spectra of individual reflections for cases in which the reflections are overlapped. Two typical SWF signals generated in aluminum plates (overlapping and non-overlapping reflections) are analyzed.

Williams, J. H., Jr.↗
NASA NTRS1986

A study of the stress wave factor technique for nondestructive evaluation of composite materials

The acousto-ultrasonic method of nondestructive evaluation is an extremely sensitive means of assessing material response. Efforts continue to complete the understanding of this method. In order to achieve the full sensitivity of the technique, extreme care must be taken in its performance. This report provides an update of the efforts to advance the understanding of this method and to increase its application to the nondestructive evaluation of composite materials. Included are descriptions of a novel optical system that is capable of measuring in-plane and out-of-plane displacements, an IBM PC-based data acquisition system, an extensive data analysis software package, the azimuthal variation of acousto-ultrasonic behavior in graphite/epoxy laminates, and preliminary examination of processing variation in graphite-aluminum tubes.

Sarrafzadeh-Khoee, A.↗
NASA NTRS1989

Rapidly quantifying the relative distention of a human bladder

A device and method of rapidly quantifying the relative distention of the bladder in a human subject are disclosed. The ultrasonic transducer which is positioned on the subject in proximity to the bladder is excited by a pulser under the command of a microprocessor to launch an acoustic wave into the patient. This wave interacts with the bladder walls and is reflected back to the ultrasonic transducer, when it is received, amplified and processed by the receiver. The resulting signal is digitized by an analog-to-digital converter under the command of the microprocessor and is stored in the data memory. The software in the microprocessor determines the relative distention of the bladder as a function of the propagated ultrasonic energy; and based on programmed scientific measurements and individual, anatomical, and behavioral characterists of the specific subject as contained in the program memory, sends out a signal to turn on any or all of the audible alarm, the visible alarm, the tactile alarm, and the remote wireless alarm.

Companion, John A.↗
DOE OSTI2021

Ultrasonic microphone and ultrasonic acoustic radio

This disclosure provides systems, methods, and apparatus related to an ultrasonic microphone and an ultrasonic acoustic radio. In one aspect a system includes a transmitter and a receiver. The receiver comprises a membrane. The membrane comprises a single layer or multiple layers of a two-dimensional material. The receiver is operable to receive sound waves in a frequency range, with the frequency range being the ultrasonic frequency range.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Ultrasonic microphone and ultrasonic acoustic radio

This disclosure provides systems, methods, and apparatus related to an ultrasonic microphone and an ultrasonic acoustic radio. In one aspect a system includes a transmitter and a receiver. The receiver comprises a membrane. The membrane comprises a single layer or multiple layers of a two-dimensional material. The receiver is operable to receive sound waves in a frequency range, with the frequency range being the ultrasonic frequency range.

Zhou, Qin↗
DOE OSTI2024

Ultrasonic microphone and ultrasonic acoustic radio

This disclosure provides systems, methods, and apparatus related to an ultrasonic microphone and an ultrasonic acoustic radio. In one aspect a system includes a transmitter and a receiver. The receiver comprises a membrane. The membrane comprises a single layer or multiple layers of a two-dimensional material. The receiver is operable to receive sound waves in a frequency range, with the frequency range being the ultrasonic frequency range.

Zhou, Qin↗