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An Ultrasonic Measurement System for the Precise Determination of the Elastic Moduli of Single Crystals

Description: The measurement of the ultrasonic wave velocities in a sufficient number of known directions in a single crystal makes possible the direct computation of the elastic moduli of the crystal. For specimens having linear dimensions on the order of 2 to 3 mm, phase comparison techniques were found useful. The equipment described is based on the technique developed by McSkimin. The measurement system is actually a type of acoustic interferometer adapted to small solid specimens, and it requires specialized electronic equipment which cannot be purchased off the shelf. (auth)
Date: May 1, 1961
Creator: Renken, C. J.
Partner: UNT Libraries Government Documents Department

The H-4, H-5, and H-6 Irradiation Experiments: Irradiation of N-Reactor Graphite, Interim Report Number 1

Description: Report regarding an experimental program by Hanford Laboratories' in order "to determine the long-term irradiation behavior of the graphite used as the moderator in N-Reactor. The primary objectives of the program are to provide data for predictions of the distortion of the N-Reactor moderator and the stress conditions which could arise from the difference in the the rate and extent of contraction between the transverse and parallel orientations of the graphite bars" (p. 1).
Date: October 1964
Creator: Helm, J. W.
Partner: UNT Libraries Government Documents Department

An explanation for the shape of nanoindentation unloading curves based on finite element simulation

Description: Current methods for measuring hardness and modulus from nanoindentation load-displacement data are based on Sneddon`s equations for the indentation of an elastic half-space by an axially symmetric rigid punch. Recent experiments have shown that nanoindentation unloading data are distinctly curved in a manner which is not consistent with either the flat punch or the conical indenter geometries frequently used in modeling, but are more closely approximated by a parabola of revolution. Finite element simulations for conical indentation of an elastic-plastic material are presented which corroborate the experimental observations, and from which a simple explanation for the shape of the unloading curve is derived. The explanation is based on the concept of an effective indenter shape whose geometry is determined by the shape of the plastic hardness impression formed during indentation.
Date: April 1, 1995
Creator: Bolshakov, A.; Pharr, G.M. & Oliver, W.C.
Partner: UNT Libraries Government Documents Department

Residual stress, strain, and faults in nanocrystalline palladium and copper

Description: Nanocrystalline Pd and Cu, prepared by inert gas condensation and warm compaction, were studied using x-ray diffraction techniques. A sample of Cu with sub-micrometer grain size produced by severe plastic deformation was also examined. The Warren-Averbach technique was used to separate the line broadening due to grain size, root-mean-squared strain, and faults. Peak shifts and asymmetry were used to determine the long range surface stresses, stacking fault probability, and twin probability. The Young`s modulus of a Pd sample was determined by an ultrasonic technique, and compared with the coarse-grained, fully-dense value.
Date: February 1, 1995
Creator: Sanders, P.G.; Witney, A.B.; Weertman, J.R.; Valiev, R.Z. & Siegel, R.W.
Partner: UNT Libraries Government Documents Department

Preliminary Strength Measurements of High Temperature Ash Filter Deposits

Description: The objective of this study is to develop and evaluate preliminary strength measurement techniques for high temperature candle filter ash deposits. The efficient performance of a high temperature gas filtering system is essential for many of the new thermal cycles being proposed for power plants of the future. These new cycles hold the promise of higher thermal efficiency and lower emissions of pollutants. Many of these cycles involve the combustion or gasification of coal to produce high temperature gases to eventually be used in gas turbines. These high temperature gases must be relatively free of particulates. Today, the candle filter appears to be the leading candidate for high temperature particulate removal. The performance of a candle filter depends on the ash deposits shattering into relatively large particles during the pulse cleaning (back flushing) of the filters. These relatively large particles fall into the ash hopper and are removed from the system. Therefore, these 1247 particles must be sufficiently large so that they will not be re-entrained by the gas flow. The shattering process is dictated by the strength characteristics of the ash deposits. Consequently, the objective of this research is to develop measurements for the desired strength characteristics of the ash deposits. Experimental procedures were developed to measure Young`s modulus of the ash deposit at room temperature and the failure tensile strain of ash deposits from room temperature to elevated temperatures. Preliminary data has been obtained for both soft and hard ash deposits. The qualifier ``preliminary`` is used to indicate that these measurements are a first for this material, and consequently, the measurement techniques are not perfected. In addition, the ash deposits tested are not necessarily uniform and further tests are needed in order to obtain meaningful average data.
Date: December 31, 1996
Creator: Kang, B.S.; Johnson, E.K.; Mallela, R. & Barberio, J.F.
Partner: UNT Libraries Government Documents Department

Effect of radiation on topopah spring tuff mechanical properties

Description: The effect of radiation on the mechanical properties of Topopah Spring tuff was investigated by performing uniaxial compressive tests on irradiated and control samples of the tuff from the potential repository horizon at Yucca Mountain. Test results are presented, including stress-strain curves and peak strength and Young`s modulus values. These results show that for homogeneous uncracked samples of Topopah Spring tuff, exposure to gamma radiation had no discernible effect on the unconfined partially healed subvertical caracks indicate that exposure may reduce the strength and Young`s modulus significantly. This is attributed to weakening of the cementing materials in the cracks and fractures of the samples that were irradiated. These results are preliminary, and additional studies are warranted to evaluate whether radiation weakens cementing materials in welded tuff.
Date: November 1, 1996
Creator: Berge, P.A. & Blair, S.C.
Partner: UNT Libraries Government Documents Department

Practical limitations to indentation testing of thin films

Description: A method that is becoming increasingly common for measuring the mechanical behavior of thin films is low-load indentation testing. However, there can be complications in interpreting the results as many factors can affect hardness and moduli measurements such as surface roughness and determination of the indentation contact area. To further the understanding, the mechanical properties of thin (50 nm) films of AlN on sapphire substrates were evaluated using a scanning force microscopy (SFM) based pico-indentation device to allow imaging of the surface and indentations. The primary emphasis was the types of problems or limitations involved in testing very thin, as deposited films in which properties are desired over indentation depths less than 50 nm.
Date: November 1, 1998
Creator: Schneider, J.A.; McCarty, K.F.; Heffelfinger, J.R. & Moody, N.R.
Partner: UNT Libraries Government Documents Department

Indentation modulus and yield point of Au(111), (001), and (110)

Description: Nanoscale indentation experiments were performed on Au using the Interfacial Force Microscope (IFM) in an indentation mode. The indentation modulus and yield point were measured for three orientations of the Au surface: (111), (110), and (001). The indentation modulus for the (111) surface was found to be 36% greater than for the (001) surface and only 3% higher than the (110) surface. Additionally, the yield point was found to vary between orientations, but the shear stress resolved on {l_brace}111{r_brace} slip planes beneath the indenter on the axis of symmetry was found to be approximately 1.8 GPa for yield points of all three orientations.
Date: December 31, 1997
Creator: Kiely, J.D. & Houston, J.E.
Partner: UNT Libraries Government Documents Department

A modified direct method for the calculation of elastic moduli of composite materials

Description: The modified direct method is a scheme for the estimation of elastic moduli of composite materials and is based on micromechanical theory and classical elasticity. Using the statistical homogeneous assumption and the two-phase composite approach, one takes the average field of the composite. Due to the complexity of composite materials, the modeling parameters for the exact analytical theory are not always available and then the effective bounds are usually too wide for practical application. For engineering purposes a more practical and general model is desired. The modified direct method was developed to approach the above requirements. In this work the modified direct method is compared with different available experiment data and methods, for example, Kuster-Toksoez, Christensen-Lo. The comparison results show that the modified direct method provides a very good estimation of the elastic moduli in different kinds of problems, such as the soft and hard inclusion cases, porous materials, at various concentrations and/or various porosities.
Date: February 1, 1996
Creator: Wang, J.A.; Lubliner, J. & Monteiro, P.J.M.
Partner: UNT Libraries Government Documents Department

Elastic constants of a Laves phase compound: C15 NbCr{sub 2}

Description: The single-crystal elastic constants of C15 NbCr{sub 2} have been computed by using a first-principles, self-consistent, full-potential total energy method. From these single-crystal elastic constants the isotropic elastic moduli are calculated using the Voigt and Reuss averages. The calculated values are in fair agreement with the experimental values. The implications of the results are discussed with regards to Poisson`s ratio and the direction dependence of Young`s modulus.
Date: April 1, 1997
Creator: Ormeci, A.; Chu, F.; Wills, J.M.; Chen, S.P.; Albers, R.C.; Thoma, D.J. et al.
Partner: UNT Libraries Government Documents Department

Earth solids and dynamic nonlinear elasticity

Description: The authors` intention is to describe several manifestations of nonlinear behavior in rock. Nonlinear response may manifest itself in a variety of manners, including a nonlinear stress-strain relation, nonlinear attenuation, harmonic generation, resonant peak shift and slow dynamics, all of which are related. The authors have ample evidence that the responsible mechanism for nonlinear response [to first order] is the presence of compliant features and the influence of fluid. They define compliant features as those features that are the weakest in the rock, e.g., grain-to-grain contacts, low aspect ratio cracks, joints, etc. In addition, there may be other mechanisms responsible as yet unidentified. In the following, the authors emphasize the robust nature of observations by illustrating several experimental examples. They do not review the related theoretical framework. Finally, they do not present nonlinear parameters derived from these experiments as the purpose in this paper is to illustrate rather than quantify nonlinear response.
Date: May 1, 1997
Creator: Johnson, P.A. & Abeele, K.E.A. Van Den
Partner: UNT Libraries Government Documents Department

Characterization of aging in organic materials on atomic-, meso- and macro-length scales by {sup 13}C NMR spectroscopy

Description: A fundamental understanding of aging in an organic material requires that one understand how aging affects the chemical structure of a material, and how these chemical changes are related to the material`s macroscopic properties. This level of understanding is usually achieved by examining the material on a variety of length scales ranging from atomic to meso-scale to macroscopic. The authors are developing and applying several {sup 13}C nuclear magnetic resonance (NMR) spectroscopy experiments to characterize the aging process of organic materials over a broad range of length scales. Examples of studies which range from atomic to macroscopic will be presented.
Date: October 1, 1997
Creator: Assink, R.A.; Jamison, G.M.; Alam, T.M. & Gillen, K.T.
Partner: UNT Libraries Government Documents Department

Monte Carlo calculations of the anisotropic engineering moduli for crystalline RDX (0 GPa {le} p {le} 4 GPa)

Description: Isothermal-iosbaric Monte Carlo calculations are used in conjunction with an expression that relates the elastic stiffness tensor to the mean-square fluctuations of the strain tensor to obtain first principles predictions of the Young`s moduli, shear moduli, and Poisson`s ratios for room-temperature crystalline RDX. The results are based on numerical data obtained during previously reported calculations of the hydrostatic compression of RDX over the pressure domain 0 GPa {le} p {le} 4 GPa. Although there are no experimental data available for comparison, the predicted values of the engineering coefficients are in accord with general expectations for brittle molecular crystals. The calculations reported here are preliminary: more extensive Monte Carlo realizations are needed to yield well-converged predictions; these are underway for RDX and {beta}-HMX.
Date: December 1998
Creator: Bennett, C. M. & Sewell, T. D.
Partner: UNT Libraries Government Documents Department

Carbon syntactic foam mechanical properties testing

Description: This project was started early in the redevelopment of the carbon syntactic foam. The new mixture of carbon microballoons with the APO-BMI resin had not been fully characterized, but that was the actual purpose of this effort. During the forming of the billets for these tests, a problem began to surface; but full understanding of the problem did not evolve until samples were cured and tests were conducted. Material compressive strengths varied between 200 and 990 psi where anything below 700 was rejected. The cure cycle was adjusted in an iterative manner in an attempt to maximize the material strength. The result of this effort was that the material strength was almost doubled and was achieving strengths of 1,500 psi toward the end of the parts produced. As a consequence, some of the strength tests actually run and reported in the text of this report may not reflect data that would be obtained today. The material strength was continuously being improved over the entire year. A complete series of compression test data is reported, but subsequent tensile and flexural strength tests were not repeated. At a time when it is considered that there are no further changes to be incorporated, a repeat of these tests would be warranted. Some development remains to be done on the carbon microballoon material. Improved carbon material is now available and its effect of the material strength should be evaluated.
Date: January 1998
Creator: McEachen, G. W.
Partner: UNT Libraries Government Documents Department

Effect of sample test volume and geometry on the tensile mechanical behavior of SiC/SiC continuous fiber ceramic composites. Final report

Description: The development of a silicon carbide-type fiber from an organometallic precursor has led to a major resurgence of interest in fiber-reinforced ceramic matrix composites. By combining this high strength fiber with a variety of ceramic matrices it has been possible to achieve tough composites offering significant potential advantages over monolithic ceramics and carbon-carbon for high temperature applications. A continuous-fiber ceramic matrix composite (CFCC) typical of materials proposed for such industrial applications as power generation, heat recovery and chemical production as well as biomedical and environmental applications was tested in uniaxial tension using a universal test machine. Test parameters investigated included: test mode (load versus displacement), test rate (0.003 mm/s, 0.03 mm/s, 50 N/s and 500 N/s), specimen geometry (straight-sided versus reduced-gauge section) and type of specimen volume (long/thin versus short/fat). Typical properties include an average elastic modulus 130 {+-} 10 Gpa, an average proportional limit stress of 45 {+-} 20 Mpa, an average ultimate tensile strength of 180 {+-} 20 MPa and an average modulus of toughness of 8.4 {+-} 2 (x10{sup 5})J/m{sup 3}.
Date: September 1, 1998
Creator: Sankar, J.; Kelkar, A.D. & Neogi, J.
Partner: UNT Libraries Government Documents Department

Estimates of in situ deformability with an NX borehole jack, Spent Fuel Test - Climax, Nevada test site

Description: A series of borehole modulus measurements was obtained at the Spent Fuel Test - Climax (SFT-C) facility following removal of heat sources and a subsequent 1-year cooling period. A total of 212 measurements were obtained using a standard hardrock NX borehole (Goodman) jack. The results of 64 measurements made at the site before heating were reanalyzed for comparison with the post-heat data. Modulus values were calculated from the straight-line portion of the pressure vs displacement curves. Although the deformation modulus was observed to be highly variable, models were developed to explain much of this variability. Typically, spacial effects, anisotropy, and heating effects were present. The test results indicate that the deformation modulus tended to increase in the pillars between the underground openings where temperatures increased about 10{sup 0}C above the ambient 24{sup 0}C during the SFT-C. Conversely, a decrease in modulus was observed where temperatures were near 60{sup 0}C for a three-year period. In most cases, we found the modulus values to be slightly higher for vertical than for horizontal loading. There was a tendency for the modulus to be lower near excavated openings. While this effect was not ubiquitous, it was statistically significant.
Date: December 1, 1985
Creator: Patrick, W.C.; Yow, J.L. Jr. & Axelrod, M.C.
Partner: UNT Libraries Government Documents Department

Tensile behavior of nanocrystalline copper

Description: High density nanocrystalline copper produced by inert gas condensation was tested in tension. Displacements were measured using foil strain gauges, which greatly improved the accuracy of the strain data. The Young`s modulus of nanocrystalline copper was found to be consistent with that of coarse-grained copper. Total elongations of {approx} 1% were observed in samples with grain sizes less than 50 nm, while a sample with a grain size of 110 nm exhibited more than 10% elongation, perhaps signifying a change to a dislocation-based deformation mechanism in the larger-grained material. In addition, tensile tests were performed as a function of strain rate, with a possible trend of decreased strength and increased elongation as the strain rate was decreased.
Date: November 1995
Creator: Sanders, P. G.; Weertman, J. R. & Eastman, J. A.
Partner: UNT Libraries Government Documents Department