Internal friction Q factor measurements in lunar rocks

Investigations to aid in the interpretation of seismic data obtained below the lunar surface are reported. Fine grained basalt with about 1.0% open core porosity was encapsulated under hard vacuum and measured. A Q value just under 2,000 at 0.5 kbar was achieved for a terrestrial analog of lunar basalt. In contrast to the modulus which increases by as much as 10%, the quality factor Q shows little or no change with pressure (a well outgassed sample maintains a high Q, whereas one exposed to laboratory atmosphere maintains a low Q). This result suggests that the absence of volatiles plays an important role in determining the q factor even at a depth of 10 km below the lunar surface

Internal friction Q factor measurements in lunar rocks

In order to better interpret recently reported values for the variation of seismic Q as a function of depth below the lunar surface, we have developed apparatus and made laboratory measurements of Q as a function of hydrostatic pressure, temperature and frequency. Our measurements of the Q associated with shear deformations have demonstrated that the large difference in Q between well outgassed and volatile rich rocks persists to pressures corresponding to a depth of at least 50 km. Here we report new measurements of Q as a function of temperature, on the development of techniques to measure the Q associated with extensional deformations under hydrostatic pressure, on the derivation of theoretical relations between our laboratory Q values and the attenuation coefficient of seismic waves, and on the development of a model for mechanism of adsorption

Ultrasonic characterization of microstructure in powder metal alloy

The ultrasonic wave propagation characteristics were measured for IN-100, a powder metallurgy alloy used for aircraft engine components. This material was as a model system for testing the feasibility of characterizing the microstructure of a variety of inhomogeneous media including powder metals, ceramics, castings and components. The data were obtained for a frequency range from about 2 to 20 MHz and were statistically averaged over numerous volume elements of the samples. Micrographical examination provided size and number distributions for grain and pore structure. The results showed that the predominant source for the ultrasonic attenuation and backscatter was a dense (approx. 100/cubic mm) distribution of small micropores (approx. 10 micron radius). Two samples with different micropore densities were studied in detail to test the feasibility of calculating from observed microstructural parameters the frequency dependence of the microstructural backscatter in the regime for which the wavelength is much larger than the size of the individual scattering centers. Excellent agreement was found between predicted and observed values so as to demonstrate the feasibility of solving the forward problem. The results suggest a way towards the nondestructive detection and characterization of anomalous distributions of micropores when conventional ultrasonic imaging is difficult. The findings are potentially significant toward the application of the early detection of porosity during the materials fabrication process and after manufacturing of potential sites for stress induced void coalescence leading to crack initiation and subsequent failure

Internal friction and modulus in rocks at depth

Experimental results relevant to the seismic wave attenuation observed for the lunar crust are presented along with some results bearing on the mechanism by which the presence of volatiles increases the attenuation

Lunar sample analysis

Previous studies have shown that very small amounts of absorbed volatiles only removed by outgassing in high vacuum and elevated temperatures-drastically increase the internal friction in terrestrial analogs of lunar basalt. Recently room temperature Q values as high as 2000 were achieved by thorough outgassing procedures in 10 to the 8th power torr. Results are presented on Q measurements for lunar rock 70215.85, along with some data on the effect on Q of a variety of gases. Data show that substantially greater increases in Q are obtainable in a lunar rock sample than in the terrestrial analog samples studied, and that in addition to H2O other gases also can make non-negligible contributions to the internal friction

High Frequency Ultrasonics

A high frequency 250 MHz A-scan system has been used for flaw detection. We have been able to detect 25-500 ~m defects of different types (C, Si, SIC, BN, Fe, WC) in a Si3N4 plate. Since it is difficult to determine the defect type and size from the amplitude of the backscattered signal , we have carried out Fourier transforms of the backscattered signal to obtain reflectivity as a function of frequency, and used that information to characterize the size and type of defect. Our ea~ly experiments have been with voids in glass and Si 3N4 and we are able to predict the size of the defects we detect

Ultrasonic NDE of Laser-Damaged Organo-Matrix Composites

The ultrasonic attenuation and velocity in graphite/epoxy (Gr/Ep) composites damaged by real and simulated laser radiation were measured. The measurements were carried out with composite ultrasonic test equipment (CUTE), a water-tank testbed constructed to study the elastic properties of samples subjected to CO2 laser radiation at several different scan rates. Parallel simulation studies were carried out on samples subjected to temperatures high enough to cause pyrolysis. The ultrasonic measurements were made in the 1 to 5 MHz frequency range for varying angles of incidence. The damage manifests itself in differing degrees of porosity depending on the intensity of irradiation. Both attenuation and velocity were found to be sensitive to this damage.</p

PVP2004-2833 Locomotive Wheel Inspection with EMAT Technology

ABSTRACT There is a need to analyze locomotive wheels for flank cracks in a non-destructive manner in order to prevent catastrophic failures. Flaw, shape, and size are desired parameters in estabfishing the cp/ality of cormnercial tires. A variety of defects such as voids, inclusions, surface and internal cracks, or the like, must be discerned in order to prevent failure. This paper exhibits and compares the benefits of a number of different techniques used for flaw detection. Non-destructive evaluation (NDE) techniques used are magnetic particle inspection, dye penetrant, eddy current, electro-magnetic acoustic transducer (EMAT). The techniques vary in their ability to ascertain the flaw characterishcs. Using a non-contact sensor such as the EMAT, to scan the wheels in an automated manner offers greater inspection speed at lower manpower. This paper reviews the basic concept of EMATs, introduces a recently developed technique for simulating EMAT performance by Finite Element calculation and features bench top results of waveform acquisition and signalto-noise ratio dependence on lift-off. Next presented are calibration results for spark -eroded flaws in wheel sections for a variety of locations and sizes. Finally data are on flaw detection in a railroad service facility on several locomotives with wheels spinning at speeds up to 40 meters/minute. Results for both artificial and actual flaws are shown

PVP2004-2823 DESIGN AND PERFOMANCE OF A BROADBAND 10MHZ TRANSDUCER FOR ELEVATED TEMPERATURE, LEAVE-IN-PLACE APPLICATIONS

Abstract This paper describes the novel design of an ultrasonic normal beam transducer for prolonged use in elevated temperature environments. Through the use of a Carbon/Carbon composite backing layer, prolonged exposure to elevated temperature had minimal effect on transducer performance. The conductive nature of the Carbon/Carbon allowed for an innovative electrical coupling technique. A clamping mechanism combined with the use of an annealed gold quarterwave matching layer allowed for joint-free, dry coupling. This simple design allows for easy field assembly and eliminates temperature dependencies in the acoustic coupling. The transducer was tested initially at room temperature for reference data. Further tests after 100+ hours of exposure to a 77°C environment showed little overall change in the transducer performance. The transducer showed consistent -6dB bandwidths on the order of 54-67%, along with negligible change in centedine frequency. The insertion loss as a function of temperature showed an increase from approximately 6.8dB to 0 0 8.5dB over a temperature range from 25 C to 85 C. Regression lines show bandwidth cha~ges of-0.01% per °C and insertion loss changes of 0.03dB per C. These results show potential use for a transducer of this design at even higher temperatures

Ultrasonic Imaging and the Long Wavelength Phase

Elastodynamic and acoustic wave scattering play an essential role in various inspection methods such as sonar and ultrasonic tomography. Recently there has been considerable interest in the implications of long wavelength elastodynamic scattering for the characterization of flaws in elastic solids [1-6]. If the scattering amplitude is expanded as a power series in the frequency, the leading term is real and varies as the frequency squared. The next term varies as the frequency cubed and is purely imaginary. The evaluation of the phase variation in the long wavelength limit requires the ratio of these terms. Most effort to date has been invested in understanding the dependence of the coefficient of the frequency squared term on the size, shape, orientation and material properties of the scatterer. Richardson [3] and Kohn and Rice [4] have shown that, for an anisotropic elastic inclusion in an otherwise isotropic and homogeneous elastic space, the coefficient depends on at most 22 parameters. In addition, efficient numerical programs have been constructed to evaluate this coefficient for ellipsoidal inclusions. Other work has related it to the stress intensity factor for flaws which are crack-like [5]