Showing papers by "Wright-Patterson Air Force Base published in 1972"

Synthesis and Mechanical Properties of Stoichiometric Aluminum Silicate (Mullite)

Abstract: Highly dense translucent polycrystalline bodies of stoichiometric aluminum silicate (mullite) were obtained by vacuum-hot-pressing of high-purity submicron mixed oxide powders. The powders were prepared by the hydrolytic decomposition of mixed metal alkoxides. X-ray diffraction and electron microscopy indicated that the initially amorphous needlelike fine particulates transform into highly crystalline orthorhombic mullite at ∼1200°C. Optimum hot-pressing conditions were 5 kpsi and 1500°C for 30 min. Densities within experimental error of the theoretical value of 3.19 g/cm3 were obtained. A typical microstructure consisted of fine interlocking needlelike grains arranged in an overall mosaic or “jigsaw” pattern. Microprobe traverses across the samples indicated homogeneous dispersion of SiO2 in the AlO3 matrix. Room-temperature mechanical properties were measured and correlated with the microstructure and crystal structure of the ceramic compact. A slightly higher melting temperature than has been previously reported was observed for the 3Al2O3·2SiO2 studied. All specimens exhibited a smooth surface finish and excellent thermal-shock resistance from 1200°C to room temperature.

Stress Analysis of Thick Laminated Composite and Sandwich Plates

Abstract: Because of the relatively soft interlaminar shear modulus in high per formance composites, laminated plate theory based on the Kirchhoff hypothesis becomes inaccurate for determining gross plate re...

X-Ray Band Spectra and Molecular-Orbital Structure of Rutile Ti O 2

Abstract: A complete molecular-orbital energy-level diagram for Ti${\mathrm{O}}_{2}$ is empirically deduced from the combined $\mathrm{Ti}{L}_{\mathrm{III}}$, $\mathrm{Ti}K$, and $\mathrm{O}K$ x-ray emission and absorption band spectra. All of the occupied and vacant orbitals within 25 eV of ${E}_{F}$ are located on a relative energy scale. The titanium $3d$, $4s$, and $4p$ states and the oxygen $2s$ and $2p$ states all play important roles in the chemical bonding and all have specific influences on the x-ray bands. The deduced energy-level diagram is also shown to be compatible with the optical-absorption, photoconductivity, optical-reflectivity, and ultraviolet photoemission spectra.

Human engineering the keyboard.

Abstract: The standard typewriter keyboard serves as a model for keyboards of teletypewriters, desk calculators, consoles, computer keysets, cash registers, etc. This man-machine interface should be designed...

The mechanism of void formation, void growth, and tensile fracture in an alloy consisting of two ductile phases

Abstract: An investigation has shown that it is possible to relate void formation, void growth, and tensile ductility to microstructural features in an α-β titanium alloy, Ti-5.25A1-5.5V-0.9Fe-0.5Cu, heat treated to a constant yield strength. Equations relating tensile void growth rates to microstructure for both equiaxed,E, and Widmanstatten plus grain boundaryα, W + ITG. B.,in aged β morphologies have been derived. A mechanism for void formation at α-β interfaces is presented which accounts for the observed fact that voids do not form at Widmanstatten α platelets. Tensile fracture is shown to be intergranular in nature and occurs when a critical crack length-stress relationship is satisfied. The amount of ductility achievable in a specimen depends upon the rate of void growth. If the rate is large, the void reaches a critical size for fracture at a lower applied stress and strain and hence the ductility is less.

Cold‐Pressing and Low‐Temperature Sintering of Alkoxy‐Derived PLZT

Abstract: Multiorganometallic compounds were used to prepare high-purity submicron-size lead lanthanum zirconate-titanate (PLZT) powders which can be consolidated at low sintering temperatures to high-density piezoelectric and electrooptic ceramic bodies. Simultaneous hydrolytic decomposition of lead isoamyloxide, lanthanum isopropoxide, and zirconium and titanium tertiary amyloxides produced quaternary titanate powders with particle sizes of 75 to 300 A and analyzed purity of 99.92%; the major contaminant was Na from an intermediate reaction product. Homogeneity and stoichiometry of the powders before and after processing were demonstrated by electron microscopy and chemical analysis. High-temperature X-ray diffraction indicated an amorphous material up to ∼600°C, where the crystalline phase was first observed. Powders prepared in this manner sintered to high-density fine-grained transparent bodies with uniform microstructure. The experimental results suggest that less rigorous consolidation methods are required with high-purity homogeneous precursor materials with fine particle size.

Displacement Thresholds in ZnO

Abstract: Two displacement thresholds have been observed in ZnO single crystals. Above the lower energy threshold of 310 keV, the carrier removal rate increases quadratically with increasing electron beam energy. Above the second threshold at 900 keV, a sharp reduction in the free carrier microwave absorption is observed. Accompanying this, the EPR resonances for several iron group impurities and for the F+ center (ionized oxygen vacancy) become activated and are observable. The color centers which have been associated with F centers are also activated. After a thermal anneal to remove these color centers, irradiation at lower energies yields the same energy dependence for the production of F+ centers as is observed with the electrical measurements as well as the same threshold at 310 keV. The lower threshold at 310 keV is associated with oxygen displacements while the upper threshold at 900 keV is associated with zinc displacements. On the basis of these assignments, a value for the maximum atomic recoil energy of 57 eV is obtained for both zinc and oxygen displacements.

Material Phase Transformation Effects upon Performance of Spaced Bumper Systems

Abstract: 10 Carriere, P. and Sirieix, M., "Facteurs d'lnfluence du Receullement d'un Ecoulement Supersonique," Proceedings of the 10th International Congress of Applied Mechanics, Stresa, Italy, 1960. 11 McDonald, H., "An Analysis of the Turbulent Base Pressure Problem in Supersonic Axisymmetric Flow," The Aeronautical Quarterly, Vol. XVI, May 1965, pp. 97-121. 12 Korst, H. H., Chow, W. L. and Zumwalt, G. W., "Research on Transonic and Supersonic Flow of a Real Fluid at Abrupt Increases in Cross Section (With Special Consideration of Base Drag Problems)," ME TR 392-5, Oct. 1964, University of Illinois, Urbana, 111. 13 McDonald H. and Hughs, P. F., "A Correlation of High Subsonic Afterbody Drag in the Presence of a Propulsive Jet or Support Sting," Journal of Aircraft, Vol. 2, No. 3, May-June, 1965, pp. 202-207. Dixon, R. J. and Page, R. H., "Interdependence of Base Pressure and Base Heat Transfer," ARS Journal, Vol. 31, No. 12, Dec. 1961, pp. 1785-1786. 15 Collines, D. J., Lees, L. and Roshko, A., "Near Wake of a Hypersonic Blunt Body with Mass Additions," AIAA Journal, Vol. 8, No. 5, May 1970, pp. 833-842. 16 Mueller, T. J., United Aircraft Research Laboratory, East Hartford, Conn. 1965, unpublished data.

Boundary-Layer Separation on Slender Cones at Angle of Attack

Abstract: 6 McClure, J. D., "On Perturbed Boundary Layer Flows," Fluid Dynamic Research Lab. Rept. 62-2, July 1962, MIT, Cambridge, Mass. 7 Lighthill, M. J., "Reflection at a Laminar Boundary Layer of a Weak Steady Disturbance to a Supersonic Stream, Neglecting Velocity and Heat Conduction," Quarterly Journal of Mechanics and Applied Mathematics, Vol. 3, No. 3, March 1950, pp. 302-325. 8 Lighthill, M. J., "On Boundary Layers and Upstream Influence II Supersonic Flows Without Separation," Proceedings of the Royal Society, Vol. 217, 1953, pp. 478-507, 9 Benjamin, T. B., "Shearing Flow Over a Wavy Boundary," Journal of Fluid Mechanics, Vol. 6, No. 2, 1959, pp. 161-205. 10 Lees, L. and Reshotko, E., "Stability of the Compressible Laminar Boundary Layer," Journal of Fluid Mechanics, Vol. 12, No. 4, 1962, pp. 555-590. 11 Inger, G. R., "Discontinuous Supersonic Flow Past an Ablating Wavy Wall," AIAA Journal, Vol. 7, No. 4, April 1969, pp. 762-764. 12 Inger, G. R., "Rotational Inviscid Supersonic Flow Past a Wavy Wall," Bulletin of the American Physical Society, Vol. 13, No. 11, Nov. 1968, p. 1579. 13 Martellucci, H., Rie, H., and J. F. Somtowski, J. F., "Evaluation of Several Eddy Viscosity Models through Comparison with Measurements in Hypersonic Flows," AIAA Paper 69-688, San Francisco, Calif., 1969. 14 Brown, W. B., "Stability of Compressible Boundary Layers," AIAA Journal, Vol. 5, No. 10, Oct. 1967, pp. 1753-1759. 15 Lew, H. G. and Li, H., "The Role of the Turbulent Viscous Sublayer in the Formation of Surface Patterns," Rept. R68SD12, June 1968, General Electric Missle and Space Div., Valley Forge, Pa. 16 Klein, E. J., "Liquid Crystals in Aerodynamic Testing," Astronautics and Aeronautics, Vol. 6, No. 7, July 1968, pp. 20-25. 17 Williams, E. P. and Inger, G. R., "Investigations of Ablation Surface Cross Hatching," SAMSO TR-70-246, June 1970, McDonnell Douglas Astronautics, Huhtington Beach, Calif.

Free-Edge Delamination of Tensile Coupons

Abstract: It has been experimentally observed [1, 2, 3], that both the in-plane uniaxial static and fatigue strength of orthotropic symmetrically laminated composites (i.e., in the usual notation A16=A2 6=B..=O) are a function of the ply stacking sequence. Pagano and Pipes [4] have attributed this phenomenon to the interlaminar stresses induced at the free-edge of a flat coupon. They also outlined a procedure for qualitatively assessing the nature of the free-edge stresses and optimizing laminate stacking sequence for protection against free-edge delamination. It is the purpose of this note to present experimental data on 90°, ± 45° graphite/epoxy laminates of differing stacking sequence and to interpret the results in terms of the procedure described by Pagano and Pipes [4]. The particular laminate orientation was chosen because it is of practical engineering interest and it also produces significant interlaminar normal stresses at the free-edge when subjected to a uniaxial tensile load. Consider a composite laminate constructed of Hercules’ HT-S graphite fiber and Union Carbide’s ERL-2256 epoxy resin system. The following unidirectional ply properties are obtained for 53% fiber volume content.

uv photoemission measurements of the upper d levels in the IIB-VIA compounds

Abstract: Photoemission measurements have been made of the upper $d$ levels in ZnO, ZnSe, ZnTe, CdS, CdSe, CdTe, HgSe, and HgTe using 21.2-eV (584-\AA{}) and 16.8-eV (740-\AA{}) radiation. All the samples except for HgSe and HgTe were cleaved and measured in an oil-free ion-pumped vacuum system at a pressure in the ${10}^{\ensuremath{-}7}$-${10}^{\ensuremath{-}8}$ Torr range. The results agree extremely well with values obtained by x-ray-induced-electron-emission spectroscopy. The spectra obtained for HgSe and HgTe make it possible to positively verify the identification of certain peaks observed in photoemission spectra of the IIB-VIA compounds as being due to the upper $d$ levels. The photoemission results reported in this study are also compared with both reflectivity and energy-loss measurements to obtain information about the optical density of states in the conduction bands of these compounds.

Heat transfer in a channel with a porous wall for turbine cooling application

Abstract: A method of cooling turbine blades internally by continuous injection through an interior baffle is analyzed. The analytical model consists of a two-dimensional channel formed by a solid wall (blade surface) and a porous plate (injection source). Based on incompressible- and laminar-flow assumptions, the velocity and the temperature fields are determined. The Nusselt numbers for a power-law surface-temperature variation are obtained and expressed in terms of the Prandtl and the Reynolds numbers. A related problem of cooling the turbine disk is also solved.

Human Response to Whole-Body Vibration:

Abstract: Research concerning several types of human response to whole-body vibration is reviewed and evaluated. Major emphasis is on two categories of behavioral research, subjective judgments of vibration intensity and the effects of vibration on human performance. Discussion of the biodynamic response of the human body to vibration provides background information to aid the reader in understanding and interpreting vibration parameters and results of behavioral studies. Also included are considerations of the mechanisms through which vibration affects behavioral response, and some problems and shortcomings in human vibration research.

Two-Component Vortex Flow Studies of the Colloid Core Nuclear Rocket

Abstract: Experiments with highly loaded solid-gas vortex flows are described. By application of end wall gas injection, solid to gas mass density ratios of the order of 100:1 have been obtained in the vortex with very small particle loss rates. Particle density distributions within the vortex were measured by x-ray absorption. Experimental data suggest a rotating fluidized bed model for the particle containment process. This concept is used to extrapolate present results to the aeromechanical design of a colloid core reactor suitable as a nuclear rocket engine. Nomenclature cf = coefficient of friction D = particle diameter h = axial length of chamber hc = heat-transfer coefficient for fluidized bed M = total powder mass in vortex m = total gas flow rate into chamber rnew = gas flow rate into end wall injection system R = outer radius of vortex r = radius T = temperature / = time a = cfT0pR/R2p p = cfT0/Rh Ta = circulation of injected gas at periphery Fr = vortex circulation at r e = void fraction A = particle loss rate coefficient /z — gas viscosity p = powder density p — average powder density in fluidized bed pg — gas density pp = material density of particle o> = angular velocity

Domain structure and polarization reversal in films of ferroelectric bismuth titanate

Abstract: A preliminary study has been made of the structure, optical properties and polarization reversal behavior of epitaxial bismuth titanate films grown by sputtering on MgO substrates. As grown, the films are twinned on a coarse scale, with alternate regions oriented with the monoclinic (100) and (010) plane parallel to the (110) MgO surface. Optical birefringence measurements on these regions yielded Δna and Δnb values as a function of temperature which were in general agreement with those measured for bulk crystals. By annealing film sections detached from the substrate, a single orientation of the type (010) was obtained, and regions of such samples could be poled to a single-domain condition. Hysteresis data, with the field applied along the a and c axes, for single domain regions yielded spontaneous polarization results comparable to those reported previously for bulk crystals, but indicated somewhat higher coercive fields. Similar measurements with the field along the [101] axis showed that it is possib...

On the determination of the mechanical properties of materials at high shear-strain rates

Abstract: The development and use of an experimental apparatus for testing materials in torsion at high rates-of-strain is described. Constant strain-rate data can be obtained at shear strain rates from 10 2 to 10 4 s −1 . The operation and instrumentation of a torsional split Hopkinson pressure-bar is presented along with a discussion of the accuracy and reliability of data obtained with this apparatus. In particular, the use of specimens having very short gage lengths to obtain data at high strain-rates is investigated experimentally. Data from high strain-rate tests on 2024-T351 aluminum alloy using specimens having gage lengths varying from 0–5 to 0–05 in. are all consistent and show this material to be slightly strain-rate dependent in torsion.

Low-Area Ratio, Thrust-Augmenting Ejectors

Abstract: The thrust augmentation, lift augmentation, and noise reduction characteristics of compact ejectors make them potentially attractive for propulsion lift systems; however, in the past, poor thrust augmentation results have negated the other benefits. A synthesis of an ejector's internal flow phenomena developed in this paper indicates that improved mixing and diffusion can significantly increase thrust augmentation. Experiments with an ejector employing a "hypermixing" primary nozzle confirm the analytical model's augmentation predictions and show reasonable agreement with other predicted flow characteristics. The two-dimensional primary nozzle has its slotshaped exit throat divided into alternating segments that impart left and right deflections to the primary flow to accelerate mixing. The results indicate that a properly designed ejector should give a thrust augmentation ratio near 1.075 + O.Q25(A3/AQ\ for 5 < A3/A0 < 14, where A3/A0 is the ratio of the ejector's exit area to the primary nozzle area.

Detection and recognition of colored signal lights

Abstract: Two experiments were designed to determine effective colors for stimulus lights as measured by speed of detection and accuracy of identification. In addition, the nature of the interactions between stimulus color, background color, and amount of ambient illumination was assessed. Responses to four stimulus lights (red, green, yellow, and white) were evaluated against four colored backgrounds (copper, tan, blue, and green) under two levels of ambient illumination. The overall ordering of stimulus colors as measured by speed of responding was, from fastest to slowest, red, green, yellow, and white. For errors in color naming, the order from least to most was green, red, white, and yellow. Detection and identification were more difficult under bright ambient illumination. The addition of an identification task added about 0.25 second to the response times for each color.

X-Ray Photoemission Measurements of GaP, GaAs, InAs, and InSb

Abstract: X-ray-induced electron-emission measurements were used to determine the energy levels of core electrons in GaP, GaAs, InAs, and InSb. The investigated energy range extends from the bottom of the valence band to about 1400 eV below the Fermi level. Samples were cleaned by using argon-ion bombardment, and the gold $4{f}_{\frac{7}{2}}$ electron level was used to provide an energy reference level. Chemical shifts were determined by comparing the results with previously published experimental values for the pure elements. Several spin-orbit-splitting values were experimentally determined. Two maxima in the conduction-band density of states were located with respect to the bottom of the conduction band by comparing the photoemission data for the outermost core $d$ and $p$ electrons with transition energies measured by uv absorption, uv reflectivity, and electron-energy-loss experiments. One maximum is located between 0.8 and 1.4 eV above the bottom of the conduction band depending on the compound and the other is located between 3 and 4 eV.

Effects of increasing intensity levels of intermittent and continuous 1000-Hz tones on human equilibrium.

Abstract: Human equilibrium was measured during exposure to continuous and intermittent 1000-Hz tones presented both asymmetrically (one ear) and symmetrically (both ears). Intermittency combined with asymmetry produced greater decrements in equilibrium than either variable alone. The results are interpreted as a possible demonstration of acoustic stimulation of the vestibular system.