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Showing papers by "Wright-Patterson Air Force Base published in 1973"


Journal ArticleDOI
TL;DR: In this article, a refined laminated plate theory is developed which is applicable to fiber reinforced composite materials under impact loading and includes the first symmetric thickness shear and thickness stretch motions.

410 citations


Journal ArticleDOI
TL;DR: In this article, a detailed design of a laminate specimen which can exhibit catastrophic delamination induced by interlaminar tension is presented, along with a preliminary failure hypothesis to characterize this mode of rupture and the associated experimental demonstration of the phenomena.

290 citations


Journal ArticleDOI
TL;DR: In this article, the authors extended the nonlinear behavior of unidirectional laminae of reference to that of laminated composites and compared the theory and experimental results through the analysis of uniaxial tension behavior of various laminates.
Abstract: This paper extends the nonlinear behavior of unidirectional laminae of Reference [1] to that of laminated composites. A comparison between the theory and experimental results is shown through the analysis of uniaxial tension behavior of various laminates. The effect on buckling stress owing to nonlinearity is illustrated for a ±45° angle-ply laminate with simply- supported edges.

136 citations


Journal ArticleDOI
TL;DR: In this paper, the phase transition from an amorphous material to a crystalline α-phase occurring at 1200°C for >4 h and/or 1300° to 1400°c for 2 h was observed.
Abstract: Thermal decomposition of silicon diimide, Si(NH)2, in vacuum resulted in very-high-purity, fine-particle-size, amorphous Si3N4 powders. The amorphous powder was isothermally aged at 50° to 100° intervals from 1000° to 1500°C for phase identification. Examination of ir spectra and X-ray diffraction patterns indicated a slow and gradual transition from an amorphous material to a crystalline α-phase occurring at 1200°C for >4 h and/or 1300° to 1400°C for 2 h. As the temperature was increased to ≥1450°C for 2 h, the crystalline β-phase was observed. Phase nucleation and crystallite morphology in this system were studied by electron microscopy and electron diffraction combined with TG as functions of temperature for the inorganic polymer starting materials. Powders prepared in this manner with 4 wt% Mg3N2 added as a sintering aid were hot-pressed to high-density fine-grained bodies with uniform microstructures. The optimum hot-pressing condition was 1650°C for 1 h. Silicon concentration steadily increased as the hot-pressing temperature or time was increased. A method for chemical etching for high-density fine-grained Si3N4 is described. Electrical measurements between room temperature and ∼500°C indicated dielectric constant and tan δ values of 8.3±0.03 and 0.65±0.05×10−2, respectively.

130 citations


Journal ArticleDOI
01 Jun 1973
TL;DR: An adaptive array that rejects undesired or interfering signals is presented and the results show that such an antenna system is capable of automatically rejecting interfering signals, subject only to certain basic constraints.
Abstract: An adaptive array that rejects undesired or interfering signals is presented. The array pattern is controlled by an adaptive feedback system based on a steepest descent minimization of mean-square error. Error is defined as the difference between the array output and a locally generated reference signal. Minimization of mean-square error is closely related to maximization of signal-to-noise ratio (SNR). A two-element adaptive array has been built, and its experimental performance is discussed. Typical patterns for various desired and interfering signals are shown, as well as measured transient response. Finally, some experiments showing the array behavior with modulated signals are described. The results show that such an antenna system is capable of automatically rejecting interfering signals, subject only to certain basic constraints. No a priori information about the angles of arrival of the signals is required, Detailed knowledge of the waveforms of the desired and interfering signals is also not needed, although the spectral characteristics of the desired signal must be known.

108 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of fatigue crack retardation due to variable amplitude loading spectra was studied in 7075-T6511 aluminum alloy, where precracked compact tension specimens were subjected to single and multiple peak applications of overload stress intensity values and subsequently cycled at lower stress intensities.

103 citations


Journal ArticleDOI
TL;DR: In this paper, the problem of assessing the probabilities of the various possible orders of finish of a horse race or assigning probabilities to the different possible outcomes of any multientry competition is discussed.
Abstract: The problem discussed is one of assessing the probabilities of the various possible orders of finish of a horse race or, more generally, of assigning probabilities to the various possible outcomes of any multientry competition. An assumption is introduced that makes it possible to obtain the probability associated with any complete outcome in terms of only the ‘win’ probabilities. The results were applied to data from 335 thoroughbred horse races, where the win probabilities were taken to be those determined by the public through pari-mutuel betting.

86 citations


Journal ArticleDOI
TL;DR: Fingerson, L. E., and Lewis, C. C. as discussed by the authors used an Electron Beam Probe (EMB) to measure the velocity and density of high speed flows.
Abstract: References 1 Fingerson, L. M., "A Heat Flux Probe for Transient Measurements in High Temperature Gases," Ph.D. thesis, 1961, Univ. of Minnesota, Minneapolis, Minn.; also ARS Journal, Vol. 13, No. 11, Nov. 1962, p. 1709. 2 McCroskey, W. J., "Density and Velocity Measurements in HighSpeed Flows," AIAA Journal, Vol. 6, No. 9, Sept. 1968, pp. 1805-1808. 3 Horstman, C. C. and Kussoy, M. I, "Hypersonic Viscous Interaction on Slender Cones," AIAA Paper 68-2, New York, 1968. 4 Vas, I. E., "An Experimental Investigation of the Flow About a Slender Cone at Hypersonic Speeds," Ph.D. thesis, 1970, New York Univ., New York. 5 Becker, M., Papanikas, D. G., and Schweiger, G., "Experimental Study of the Flow Field in Front of Hemispheres in the Transition and Shock Formation Regime," presented at the 7th RGDS, July 1970, Deutsche Forschungsurid Versuchsanstalt fur Luftund Raumfahrt, (DFVLR) Porz-Wahn, W. Germany. 6 Harbour, P. J. and Lewis, J. H., "Preliminary Measurements of the Hypersonic Rarefield Flow Field on a Sharp Flat Plate Using an Electron Beam Probe," Rarefied Gas Dynamics, Supp. 4, Vol. 1, Academic Press, New York, 1967. 7 Petraites, R. J., "An Experimental Investigation of the Effects of Three-Dimensionality on the Flow Over a Flat Plate at M ~ 25," MSE thesis, Aug. 1972, Dept. of Aerospace and Mechanical Sciences, Princeton Univ., Princeton, N.J. 8 Dewey, C. F., Jr., "A Correlation of Convective Heat Transfer and Recovery Temperature Data for Cylinders in Compressible Flow," International Journal of Heat and Mass Transfer, Vol. 8, 1965, pp. 245-252. 9 Rubin, S. G., Rudman, S., Lin, T. C, and Pierucci, M., "Hypersonic Viscous-Inviscid Interaction by a New Type of Analysis," AGARD CP 30, Hypersonic Boundary Layers and Flow Fields, May 1968. 10 Mayne, A. W., Jr., Gilley, G. E., and Lewis, C. H., "Binary Boundary Layers on Sharp Cones in Low-Density Supersonic and Hypersonic Flow," AIAA Journal, Vol. 7, No. 4, April 1969, pp. 699-706.

83 citations


Journal ArticleDOI
TL;DR: In this paper, a wave function basis consisting of Gaussian lobe functions is presented for performing crystalline Hartree-Fock calculations with a wave-function basis consisting in Gaussian lobe functions.
Abstract: A method is presented for performing crystalline Hartree-Fock calculations with a wave-function basis consisting of Gaussian lobe functions. The most important concepts involve (i) the utilization of crystal symmetry in characterizing the first-order density matrix, and in selective computation and efficient storage of the one- and two-electron integrals; (ii) the introduction of a charge-conserving approximation for some of the less important three- and four-center integrals over contracted Gaussian basis functions; and (iii) the imposition of monopole and dipole compensation for the most important neglected two-electron Coulomb integrals. The method is applied to diamond, and calculational results are given for various sets of parameters. The best results include a Hartree-Fock cohesive energy of 0.38 Ry/atom, a virial coefficient ($\ensuremath{-}\frac{2T}{V}$) of 1.0005 for a lattice constant of 3.56 \AA{}, a direct band gap at $\ensuremath{\Gamma}$ of 15 eV, and an indirect band gap from $\ensuremath{\Gamma}$ to $\ensuremath{\Delta}$ of 13.7 eV. The(111) Fourier transform of the charge density is 3.29 electrons per crystallographic unit cell.

83 citations


Journal ArticleDOI
TL;DR: In this article, the reaction kinetics between α-Ti alloys and single crystal sapphire, the phase composition and morphology of the reaction-zone, and the phase compatibility in the system Ti-Al-O were investigated as part of a study to determine the feasibility of fabricating useful Al2O3-reinforced titanium matrix composites.
Abstract: The reaction kinetics between α-Ti alloys and single crystal sapphire, the phase composition and morphology of the reaction-zone, and the phase compatibility in the system Ti-Al-O were investigated as part of a study to determine the feasibility of fabricating useful Al2O3-reinforced titanium matrix composites. In the temperature range 650 to 1000° C titanium reduces Al2O3 to form a complex reaction layer consisting of two distinct zones; an inner zone adjacent to the Al2O3 of a TiO phase containing isolated particles of (Ti, Al)2O3, presumably, and an outer zone of a Ti3Al phase adjacent to the Ti matrix. The isothermal growth of the reaction layer follows a parabolic rate law. The temperature dependence of the rate constants fits an Arrhenius equation yielding activation energies of 50 to 52 kcal/mol. The high Al alloys, except Ti-6Al-2Sn-4Mo-2Zr, reacted more rapidly than pure Ti indicating that Al diffusion through the reaction zone may be the rate-limiting step.

81 citations


Journal ArticleDOI
TL;DR: The feasibility of ejector propulsion-lift concepts requires the simultaneous attainment of two conflicting objectives: high performance and compactness as discussed by the authors, which led to the design of the ejector's components.
Abstract: Ejectors offer interesting means for resolving problems arising from the additional power requirements of V/STOL aircraft. They are capable not only of turning and augmenting the cruise engine's thrust vector, but their efflux can also serve to control circulation lift. The feasibility of ejector propulsion-lift concepts requires the simultaneous attainment of two conflicting objectives: high performance and compactness. Performance is degraded by losses occurring in the inlet, the primary nozzle, and the duct-diffuser of the ejector. Analytic results identified practical loss trade-offs that led to the design of the ejector's components. Static experiments with independently varied duct and diffuser lengths showed, surprisingly, that skewed flows can be diffused effectively. Augmentation ratios in excess of 1.85 were measured with a duct-diffuser 28 in. long. Increasing the length to 50 in. caused augmentation ratios to exceed 2.0.

Book ChapterDOI
TL;DR: In this article, it is argued that large, nonlinear shear strains occur at the interfaces for fiber orientations leading to near maximum shear coupling compliances, which allow the initiation of matrix cracks at the free edge, which are ultimately responsible for the premature rupture of the coupon.
Abstract: Strength characterization of the fiber-reinforced laminated composite materials is quite often accomplished through the utilization of the finite-width tension coupon specimen. Recent analytical studies have shown that the state of stress in the vicinity of the free edge of such a laminate is fully three dimensional in nature and may not be predicted by laminated plate theory. Furthermore, experimental results have revealed that while the strength of angle-ply tensile coupons of certain fiber orientations are predicted adequately by laminate strength theories, coupons of other fiber orientations are not. As an explanation of this result, it is argued that large, nonlinear shear strains occur at the interfaces for fiber orientations leading to near maximum shear coupling compliances. Further, these strains allow the initiation of matrix cracks at the free edge, which are ultimately responsible for the premature rupture of the coupon. Experimental evidence which supports these arguments is presented.

Journal ArticleDOI
TL;DR: Technical reports pertaining to flight simulator transfer of training studies available from the Defense Documentation Center are reviewed.
Abstract: Often operational equipment is considered to be the most effective and valid training equipment. However, this is not true in every instance. In fact, sometimes it may be undesirable to use real equipment for training if suitable simulators are available. For example, the use of operational equipment has several disadvantages which include (1) high costs, (2) limitation on practice of varied aspects of tasks, and (3) safety hazards. Practical decisions in the use of training devices depend upon compromises between economic and training objectives. A trainer need not duplicate operational equipment to have training value. Technical reports pertaining to flight simulator transfer of training studies available from the Defense Documentation Center are reviewed.

Journal ArticleDOI
TL;DR: In this paper, an electronic structure for the layered compound Ti${\mathrm{S}}_{2} was suggested based on the combined x-ray-emission and -absorption band spectra.
Abstract: An electronic structure, in terms of molecular orbitals, is suggested for the layered compound Ti${\mathrm{S}}_{2}$. This structure is based on the combined $\mathrm{Ti}{L}_{\mathrm{III}}$, $\mathrm{Ti}K$, $\mathrm{S}{L}_{\mathrm{II},\mathrm{III}}$, and $\mathrm{S}K$ x-ray-emission and -absorption band spectra. The x-ray data appear to be compatible with the optical reflectivity spectrum but at odds with theoretical estimates of the band structure. Although the results are empirically conjectural they are used to suggest that Ti${\mathrm{S}}_{2}$ is a metal or semimetal instead of a small-gap semiconductor.

Journal ArticleDOI
01 Mar 1973
TL;DR: This paper describes the results of experimental investigation of two-feature evaluation criteria, i.e., inter-intra class distance ratio and information content measure, and believes that the criteria can be used for other applications and can especially be used where the statistical independency among features is not assumed.
Abstract: This paper describes the results of experimental investigation of two-feature evaluation criteria, i.e., inter-intra class distance ratio and information content measure. These two indirect statistical measures take into account higher order statistical redundancies among the feature being evaluated. The algorithms are first presented and then they are applied and compared to recognize handprinted alphanumeric characters. Both Highleyman's data and raw data obtained in the Signal Processing Laboratory at Case Western Reserve University, Cleveland, Ohio, were used for the study. It is believed that the criteria can be used for other applications and can especially be used where the statistical independency among features is not assumed.

Journal ArticleDOI
TL;DR: In this article, the lowest energy gap of AgGaS2 in the temperature range from 4.2 to 300° K was determined from the reflectivity, photoluminescence and absorption measurements.

Journal ArticleDOI
TL;DR: In this article, the authors cosider the derivation of the exact distributions of the ratios of the extreme roots to the trace of the Wishart matrix, and exact percentage points of these distributions are given and their applications are discussed.

Journal ArticleDOI
TL;DR: In this article, high speed flow past a blunt protuberance on a surface results in a complex, three dimensional, inviscid-viscous interaction flow field, which is characterized by a separated flow region composed of horseshoe vortices near the surface, and a lambda-type shock pattern in the plane of symmetry ahead of the protubance.
Abstract: : High speed flow past a blunt protuberance on a surface results in a complex, three dimensional, inviscid-viscous interaction flow field. Characteristically, the interaction results in a separated flow region composed of horseshoe vortices near the surface, and a lambda-type shock pattern in the plane of symmetry ahead of the protuberance. The shock wave emanating from the separated flow region impinges on the bow shock ahead of the protuberance and causes intense heating and high pressures locally on the protuberance leading edge. The heating and pressure in this local area can be 10 times larger than the undisturbed stagnation line values; the amplification depends strongly on local flow conditions. Tests were conducted to examine and obtain a better understanding of these interaction flow fields; the most recent tests included detailed flow field surveys for Mach 3 flows ahead of blunt fins on a flat plate surface with turbulent boundary layers. (Author)

Journal ArticleDOI
TL;DR: In this article, the in-plane or longitudinal shear stress-strain response of a unidirectional composite material is determined using a cross-sandwich beam test and an angle-ply laminate subjected to uniaxial tension.
Abstract: The experimental determination of the in-plane or longitudinal shear stress-strain response of a unidirectional composite material usually presents a difficult task. Several test techniques have been proposed for determining this quantity: (1) Pure torque applied to a tubular specimen (Adams and Thomas [ 1 ] ), (2) Cross-sandwich beam test (Shockey and Waddoups [2] ), (3) Rail shear test (Whitney, Stansbarger, and Howell [ 3 ] ), and (4) ±45 balanced angle-ply laminate subjected to uniaxial tension (Petit [4] and Rosen [ 5 ] ).


Journal ArticleDOI
TL;DR: In this article, the authors present an efficient optimization method based on strain energy distribution and a numerical search for the minimum weight design of structures made from fiber reinforced composite materials, which takes into consideration multiple loading conditions and displacement constraints on the structure.

Journal ArticleDOI
TL;DR: In this paper, two thermomechanical treatments have been considered, one a high strength condition equivalent to the conventional T-6 treatment and the other an over-aged condition comparable to the T-73 treatment.

Journal ArticleDOI
TL;DR: In this article, the problem of electron-excited Auger analysis resulting from chemical alteration of the shapes of the characteristic features can be virtually eliminated by integration techniques, and these techniques recover the signal strength lost by taking data derivative modes.

Book ChapterDOI
TL;DR: In this paper, a general review of free-edge problems as related to composite characterization is presented, including a discussion of narrow versus wide specimens, where a preliminary analysis of the free edge problem reveals a state of stress which differs from a tensile coupon.
Abstract: In the use of flat specimens for the characterization of composite materials, stress free edges often are encountered. In the case of laminated tension specimens, such free edges induce interlaminar stresses which can disturb the desired state of stress. Large stress concentrations can be induced by free edges, such as in the rail shear test. Other examples include the sandwich beam test. A general review of free-edge problems as related to composite characterization is presented, including a discussion of narrow versus wide specimens. Particular attention is given to the sandwich beam test where a preliminary analysis of the free-edge problem reveals a state of stress which differs from a tensile coupon.

Journal ArticleDOI
TL;DR: Minimal doses of Cresatin, camphorated parachlorophenol, and formocresol were placed on cotton pellets in 10 mm tubes and implanted into the subcutaneous connective tissues in the backs of rats to determine the tissue reactions.


Journal ArticleDOI
TL;DR: In this article, a model of the fiber is diagrammed as a compromise of a fibrillar structure and ordered crystallites with tilt and sub-grain boundaries, and the surface characteristics of the graphite fibers are revealed when viewed with high magnification scanning electron microscopy (SEM).
Abstract: Means of inducing carbonyl functional groups to high modulus graphite fibers (Thornel 50) are described. One approach involves wet chemical oxidation of the fibers in aqueous sodium iodate solution. Another route to hypothesized augmented carbonyl functionality on graphite fibers proceeds through reaction of the fibers in an aqueous dioxane osmium tetroxide solution. In the latter case, coupling of graphite carbonyl to oxirane epoxy is postulated as occurring through an intermediate stannic chloride complex, Bonding of fibers to matrix is shown to be improved with little to no loss in tensile properties of the fibers. As a result of the specificity of the reactions, the surface characteristics of the graphite fibers are revealed when viewed with high magnification scanning electron microscopy (SEM). Based on such observations, a model of the fiber is diagrammed as a compromise of a fibrillar structure and ordered crystallites with tilt and sub-grain boundaries. Also described is a thermal oxidati...

Journal ArticleDOI
TL;DR: In this paper, the electrical conductivity, o-, and the total radiant power per unit volume, PR9 of air are measured for temperatures between 8,000 and 12,500°K at atmospheric pressure.
Abstract: The electrical conductivity, o-, and the total radiant power per unit volume, PR9 of air are measured for temperatures between 8,000 and 12,500°K at atmospheric pressure. The measurements are made in a wallstabilized electric arc discharge which produces a pure, stable plasma. Axial electric field strength, £,, and azimuthal magnetic field intensity, B^ are measured as functions of the discharge radius by using probe techniques. Current density, jz9 is obtained as ~]*= V x£//z0, and electrical conductivity is determined by using Ohm's law, o = jJEz. PR is measured with a total radiation thermopile and also by using an electrical technique. Plasma temperature is determined from the absolute intensities of the 4935 A NI and 4368 A OI lines.


Journal ArticleDOI
TL;DR: In this paper, the effect of rotational and translational support flexibility on the fundamental frequency of an almost-clamped clamped beam and a flexibly supported cantilever beam is considered.
Abstract: The effect of rotational and translational support flexibility on the fundamental frequency of both an almost-clamped-clamped beam and a flexibly supported cantilever beam is considered. In each case the effect of a rotationally flexible support becomes more pronounced for decreasing values of the length-to-depth ratio. It is shown that the effect of end-fixity on the fundamental frequency can be of a magnitude equal to or greater than that due to the effect of shear deformation or rotatory inertia. Results using Bernoulli-Euler beam theory and Timoshenko beam theory are compared. Expressions are formulated that give the fundamental frequency as a function of the support flexibility, length to depth ratio and fundamental frequency for a rigid support.