Showing papers by "Wright-Patterson Air Force Base published in 1974"

On the Calculation of Interlaminar Normal Stress in Composite Laminate

Abstract: In an effort to improve our understanding of delamination phenomena in composite bodies, an approximate method to define the distribution of the interlaminar normal stress, σ z, along the central plane of a symmetric, finite-width, composite laminate is presented. The approach is based upon a modified version of a recent theory developed by Whitney and Sun and accounts for the influence of the pertinent material and geometric parameters on the shape of the distribution. The accuracy of the approach is demonstrated by comparison with an existing three-dimensional elasticity solution. Finally, an elementary expression for σ z in practical bidirectional laminates is derived.

Remote Measurement of Eye Direction Allowing Subject Motion Over One Cubic Foot of Space

Abstract: The remote oculometer is a new instrument for the remote measurement of eye direction and pupil diameter. The electrooptical sensor unit is located several feet from the subject, who is free to move the eye being sensed throughout 1 ft 3 of space. The video processing is performed in real time by a standard minicomputer. The oculometer processor (minicomputer) provides automatic calibration and linearization to each subject and can, supply the output eye-direction information in the form of either fixation-point coordinates on any specified fixation plane, azimuth and elevation, or direction cosines.The oculometer measures line-of-sight to an accuracy of 1° for eye rotation angles, relative to the sensor unit, of from 0° to + 30° elevation and from -30 ° to + 30 ° azimuth.

Reliability Analysis of Aircraft Structures under Random Loading and Periodic Inspection

Abstract: A reliability analysis of fatigue-sensi tive aircraft structures, based on the application of the approach developed in the "random vibration theory," is presented. Operational service loads, composed of ground loads, ground-air-ground loads, and gust loads, are all random in nature. The fatigue process involved here consists of crack initiation, crack propagation, and strength degradation. The time to crack initiation and the ultimate strength are random variables. After a fatigue crack is initiated, fracture mechanics is applied to predict crack propagation under random loading. While the fatigue crack is propagating, the residual strength of the structure decreases progressively, thus increasing the failure rate with time. The aircraft structure is subjected to periodic inspection in service. When a fatigue crack is detected during inspection, the implicated component is either repaired or replaced, so that both the static and the fatigue strength are renewed. Such a renewal process is taken into account in the present analysis. The detection of an existing fatigue crack during inspection is also a random variable which depends on the resolution capability of the particular technique employed and the size of the existing crack. Taking into account all the random variables as well as all the random loadings, the solution for the probability of first failure in a fleet of aircraft is derived. Finally, numerical examples are given to demonstrate the effect of inspection and fleet size on the fleet reliability.

Evaluation of Hypermixing for Thrust Augmenting Ejectors

Abstract: Steady-state distortion levels produced during full scale PG operation as evaluated in terms of IDC (circumferential) and IDR (radial) distortion parameters were generally less 0.02 and nominally 0.01 or less as previously realized in the model test. Figure 10 summarizes the circumferential planarity in terms of phase and amplitude. The probe readings from two of the rakes, 180° apart, at the engine IGV plane were averaged to obtain these summary results. Such a comparison indicates excellent circumferential planarity over the complete range of the test data. A similar summary of radial planarity characteristics is presented in Fig. 11. In this case, all the probe readings from 2 selected radial immersions were averaged. Radial immersion B is the tip and D is the hub ring. The hub ring probes had the most deviation from those in any of the other rings, thus the results of Fig. 11 represent the "worst case."

Analysis of the Flexure Test for Laminated Composite Materials

Abstract: Equations applicable to a general class of symmetrically laminated beams are derived by considering a beam as a special case of a laminated plate. The beam bending stiffness thus becomes a function of all the bending stiffness coefficients of a laminated plate. The validity of this approach is verified by comparing theoretical results to flexure data on graphite/epoxy angle-ply and quasi-isotropic laminates. In addition, it is shown that flex strength on general composite laminates is extremely difficult to interpret, even though the stresses can be calculated from the modified beam theory. Discontinuities in the in-plane stresses at layer interfaces lead to a state of stress which is difficult to compare to standard laminate tensile coupons.

Optical properties of LiF

Abstract: In this paper, we examine the optical properties of LiF. The fundamental calculations performed are a self-consistent Hartree-Fock band-structure calculation. As has been found previously, such a calculation has substantial errors when compared with experiment. Correlation corrections are needed and are included by means of the electronic-polaron method. The usual electronic polaron is extended to include short-range polarization corrections which the usual model neglects but which are peculiarly large for LiF. The energy bands are evaluated directly by the linear-combination-of-local-basis-functions method along with the crystal wave functions for 89 points in the irreducible wedge of the first Brillouin zone. Using these results and the Lemann-Taut interpolation scheme the density of states, the joint density of states, and the imaginary part of the dielectric function are computed. These results which neglect the formation of excitons and "plasmons" are in poor agreement with experiment. The effect of the exciton formation is included by a Koster-Slater one-band---one-site calculation. We find that the inclusion of exciton effects substantially improves the level of agreement with experiment. This is in direct contrast with recent work of Menzel et al. in which energy-band theory alone is found to account for the optical properties of LiF. This disagreement is discussed in detail.

Hartree-Fock calculations for crystalline Ne and LiF

Abstract: The self-consistent Hartree-Fock energy bands which are presented in this paper for LiF and Ne closely match Hartree-Fock energy bands reported by other groups for these compounds. The Hartree-Fock equilibrium lattice constant and bulk modulus for LiF are 3.972 \AA{} and 7.54 \ifmmode\times\else\texttimes\fi{} ${10}^{11}$ dyn/${\mathrm{cm}}^{2}$, as compared to the experimental values of 4.02 \AA{} and 6.71 \ifmmode\times\else\texttimes\fi{} ${10}^{11}$ dyn/${\mathrm{cm}}^{2}$. Hartree-Fock x-ray structure factors and directional Compton profiles in the impulse approximation are presented. The calculated x-ray structure factors of LiF agree with experiment to within 2%, while the calculated Compton profiles of LiF agree with experiment to within 3%.

Interaction of Cracks with Rigid Inclusions in Longitudinal Shear Deformation

Abstract: The interaction of a crack with rigid circular cylindrical inclusions is considered for the case of longitudinal shear deformation General representations of the solutions for a radial crack near a single and midway between two inclusions are given The particular case of uniform shearing stress applied at infinity is discussed in detail

Optimal Multiple-Impulse Direct Ascent Fixed-Time Rendezvous

Abstract: Minimum-fuel, impulsive, direct ascent rendezvous trajectories are obtained for the fixed transfer time case. The terminal orbit is circular about a spherical nonrotating planet. The inclination and radius of the terminal orbit, the target position at launch, and the transfer time are independent parameters in the problem. Two- and three-impulse optimal solutions are obtained. The primer vector evaluated along a nonoptimal trajectory provides a gradient of the cost with respect to impulse times and locations. The Davidon-Fletcher-Powell algorithm is used to perform the minimization. For certain rendezvous geometries and transfer times the optimal three-impulse timefixed fuel cost is lower than the optimal two-impulse time-open cost.

Acute Toxicity in Rats and Mice Exposed to Hydrogen Chloride Gas and Aerosols

Abstract: Hydrogen chloride (HC1) is one of the combustion products formed during the test firing of certain rocket and missile engines. A study was undertaken to determine the LC50 values for rats and mice exposed to various measured concentrations of either HC1 gas or HC1 aerosol for 5 and 30 minutes. This accomplished two objectives; first, to define short-exposure toxicity levels for HC1 in either form and second, to determine whether the aerosol form represented a greater hazard than the gas itself. The respiratory tract was the primary target for HC1 in either form, and lesions were similar to those produced by other severe pulmonary irritants. The results indicate that HC1 gas and HCI aerosol have comparable toxicity in rats and mice. Comparison of these results with another study of HCI gas toxicity in rabbits and guinea pigs showed that HCI gas had the same degree of toxicity in mice, rabbits and guinea pigs while rats were considerably more tolerant.

Supersonic, Turbulent Boundary-Layer Separation

Abstract: Although the requirements for computer time and disk storage are still large, they are orders of magnitude less than what would be required by numerical solution with the differential formulation, so that some time-dependent, three-dimensional solutions can at least be considered within the present state of computer development. The accurate prediction of body forces at high Reynolds numbers would require unfeasible amounts of computer time and storage with a rectangular constant-mesh coordinate system and is still beyond the present development of the technique. Further work would be desirable to extend the present technique to nonrectangular, and eventually general, nonuniform curvilinear coordinate systems, so that bodies of general shape can be more efficiently treated.

Effects of Moisture on the Properties of High-Performance Structural Resins and Composites

Abstract: Graphite, boron, S-glass, and DuPont's PRD-49-III fiber reinforced composites, as well as castings of current epoxy resin systems, were evaluated to determine the effects of moisture and high humidity on their physical properties and their room- and elevated-temperature mechanical properties. All of the neat resin castings were found to absorb moisture and swell. Associated with moisture absorption is a loss in elevated-temperature tensile strength. All of the composite systems showed weight gains and thickness increases when subjected to a high-humidity environment. However, the effect of absorbed moisture on the elevated-temperature mechanical properties of composites is determined principally by fiber orientation and test method employed. Unidirectional composites may show a significant reduction of 350°F (177°C) flexural strength due to absorbed moisture, whereas a multidirectional lay-up may show only a minor loss of 350°F tensile strength after equivalent moisture absorption. Fiber-controlled composite properties are relatively unaffected by absorbed moisture whereas matrix-controlled properties are adversely affected.

A Method for Determination of Constant and Varying Friction Factors During Ring Compression Tests

Abstract: : Available mathematical analyses were applied to develop a reliable method for treating experimental results from ring compression tests with and without bulge formation for the following purposes: Quantitative evaluation of constant and varying friction factors, m, during testing; Determination of test material stress-strain curves. (Author)

Thickness Expansion Coefficients of Composite Laminates

Abstract: Fahmy and Ragai-Ellozy [1] have recently treated the problem of the thermal expansion coefficient in the thickness direction of a symmetric composite laminate. Unfortunately, however, an error has been made in their analysis. Specifically, Equation (1) of that work should take the form $${a_{3r}} = {a_T} - \frac{1}{{1 - {v_{12}}{v_{21}}}}\left[ {({v_{13}} + {v_{12}}{v_{23}})({a_{1C}} - {a_L}) + ({v_{23}} + {v_{13}}{v_{21}})({a_{2c}} - {a_T})} \right]$$ (1) in the notation of [1]. In particular, v 12 is major Poisson’s ratio.

Active flutter suppression - A flight test demonstration

Abstract: The first flight test demonstration of active flutter suppression has been successfully completed. The Control Configured Vehicles (CCV) B-52 test airplane was twice flown 10 knots faster than its flutter speed relying solely on an automatic control system for adequate damping. The design, safety considerations, mechanization, ground testing, and flight testing of the flutter mode control system are reported. Comparisons between flight test and theoretical results are presented. The system was tested at heavy and light airplane weights and tested for compatibility with simultaneous ride control, maneuver load control, fatigue reduction, and augmented stability.

On the distributions of significant digits and roundoff errors

Abstract: Generalized logarithmic law is derived for the distribution of the first t significant digits of a random digital integer. This result is then used to determine the distribution of the roundoff errors in floating-point operations, which is a mixture of uniform and reciprocal distributions.

Stability of an intracavity frequency-doubled Nd:YAG laser

Abstract: Single-mode rate equations are solved in the small-signal limit to determine the oscillation frequency and decay constant for relaxation oscillations in an intracavity frequency-doubled Nd:YAG laser. It is found that improved stability is noted for nonlinear coupling constants greater than 10-5. Eventually, cavity perturbations become critically damped with increased coupling, and oscillatory behavior disappears.

Defect Structure of Ta2O5

Abstract: Electrical conductivity, thermoelectric power, and weight change were measured for polycrystalline Ta2O5 from 900° to 1400°C. The predominant ionic and electronic defects in this temperature range are oxygen vacancies and electrons. The oxygen-vacancy and electron mobilities are 8.1 × 103exp (−1.8 eV/kT) and ∼0.05 cm2/V-s, respectively. At O2 partial pressures near 1 atm, the ionic-defect concentration is essentially fixed by the presence of lower-valence cation impurities, and the total electrical conductivity is predominantly ionic, whereas at low Po2's the conductivity is electronic and proportional to PPo2−1/6.