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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Impact damage of composite plates

A simple model to study low velocity transverse impact of thin plates made of fiber-reinforced composite material, in particular T300/5208 graphite-epoxy was discussed. This model predicts the coefficient of restitution, which is a measure of the energy absorbed by the target during an impact event. The model is constructed on the assumption that the plate is inextensible in the fiber direction and that the material is incompressible in the z-direction. Such a plate essentially deforms by shear, hence this model neglects bending deformations of the plate. The coefficient of restitution is predicted to increase with large interlaminar shear strength and low transverse shear modulus of the laminate. Predictions are compared with the test results of impacted circular and rectangular clamped plates. Experimentally measured values of the coefficient of restitution are found to agree with the predicted values within a reasonable error.

Lal, K. M.↗
NASA NTRS1949

Critical combinations of shear and direct axial stress for curved rectangular panels

A solution is presented for the problem of the buckling of curved rectangular panels subjected to combined shear and direct axial stress. Charts giving theoretical critical combinations of shear and direct axial stress are presented for panels having five different length-width ratios. Because the actual critical compressive stress of rectangular panels having substantial curvature is known to be much lower than the theoretical value, a semiempirical method of analysis of curved panels subjected to combined shear and direct axial stress is presented for use in design. (author

PLATES - STRESSES, SHEARING CURVED↗
NASA NTRS1982

Postbuckling of orthotropic composite plates loaded in compression

The nonlinear large deflection equations of von Karman are written for 'specially' orthotropic plates. The equations are then manipulated to determine the parameters required to establish postbuckling behavior. It is found that only two new parameters are needed beyond those required for buckling. By assuming trigonometric functions in one direction, the plate equations are converted into ordinary nonlinear differential equations which are solved numerically using a two point boundary problem solver that makes use of Newton's method. The postbuckling behavior is obtained for simply supported and clamped, long, rectangular, orthotropic plates covering the complete range of dimensions and material properties.

Stein, M.↗
NASA NTRS1989

On the fundamental frequency of rectangular simply-supported symmetric laminated plates

A new closed-form approximate solution for the fundamental frequency of symmetric rectangular laminates which are simply supported on all four edges is derived. The solution, obtained from eigensensitivity analysis, is expressed as a truncated Maclaurin series in the coupling stiffnesses D16 and D26. Results show that the predicted fundamental frequency is remarkably accurate. A comparison of the fundamental frequencies of four-ply symmetric angle-ply laminates calculated from the new formula with those determined from a Rayleigh-Ritz procedure yielded a maximum differential of 0.6 percent over a wide range of principal stiffness ratios, plate aspect ratios, and design angles.

Reiss, Robert↗
NASA NTRS2013

Interaction of a Rectangular Jet with a Flat-Plate Placed Parallel to the Flow

An experimental study is carried out addressing the flowfield and radiated noise from the interaction of a large aspect ratio rectangular jet with a flat plate placed parallel to but away from the direct path of the jet. Sound pressure level spectra exhibit an increase in the noise levels for both the 'reflected' and 'shielded' sides of the plate relative to the free-jet case. Detailed cross-sectional distributions of flowfield properties obtained by hot-wire anemometry are documented for a low subsonic condition. Corresponding mean Mach number distributions obtained by Pitot-probe surveys are presented for high subsonic conditions. In the latter flow regime and for certain relative locations of the plate, a flow resonance accompanied by audible tones is encountered. Under the resonant condition the jet cross-section experiences an 'axis-switching' and flow visualization indicates the presence of an organized 'vortex street'. The trends of the resonant frequency variation with flow parameters exhibit some similarities to, but also marked differences with, corresponding trends of the well-known edgetone phenomenon.

Zaman, K. B. M. Q.↗
NASA NTRS1977

Accuracy of the Kirchoff formula in determining acoustic shielding with the use of a flat plate

It has been suggested that if jet engines of aircraft were placed at above the wing instead of below it, the wing would provide a partial shielding of the noise generated by the engines relative to observers on the ground. The shielding effects of an idealized three-dimensional barrier in the presence of an idealized engine noise source was predicted by the Kirchoff formula. Based on the good agreement between experimental measurements and the numerical results of the current study, it was concluded that the Kirchoff approximation provides a good qualitative estimate of the acoustic shielding of a point source by a rectangular flat plate for measurements taken in the far field of the flat plate at frequencies ranging from 1 kHz to 20 kHz. At frequencies greater than 4 kHz the Kirchoff approximation provides accurate quantitative predictions of acoustic shielding.

Gabrielsen, R. E.↗
NASA NTRS1956

Zero-angle-of-attack Performance of Two-dimensional Inlets near Mach Number 3

An extensive program was undertaken to investigate the effect of several geometric variables on the performance of two-dimensional inlets. This investigation included inlets having single-wedge, double-wedge, and isentropic compression ramps with various side-plate configurations and subsonic diffusers. The tests were conducted over a range of Reynolds number based on inlet height from 0.50 to 2.67(sup x)10(sup 6). Generally, the performance levels of the two-dimensional inlets were somewhat below those obtained previously with comparable axisymmetric models. At Mach number 3.05 the optimum total-pressure recovery was obtained with an isentropic inlet which compressed the external flow to a Mach number of 1.88. Rectangular side plates and a long high-exit-Mach-number subsonic diffuser with filleted corners were used with this inlet. A critical total-pressure recovery of 0.71 was realized with a corresponding mass-flow ratio of 0.965. Subcritical stability to a mass-flow ratio of 0.60 was obtained.

Woollett, Richard R↗
NASA NTRS1975

Numerical techniques for the solution of the compressible Navier-Stokes equations and implementation of turbulence models

The time-splitting explicit numerical method of MacCormack is applied to separated turbulent boundary layer flow problems. Modifications of this basic method are developed to counter difficulties associated with complicated geometry and severe numerical resolution requirements of turbulence model equations. The accuracy of solutions is investigated by comparison with exact solutions for several simple cases. Procedures are developed for modifying the basic method to improve the accuracy. Numerical solutions of high-Reynolds-number separated flows over an airfoil and shock-separated flows over a flat plate are obtained. A simple mixing length model of turbulence is used for the transonic flow past an airfoil. A nonorthogonal mesh of arbitrary configuration facilitates the description of the flow field. For the simpler geometry associated with the flat plate, a rectangular mesh is used, and solutions are obtained based on a two-equation differential model of turbulence.

Baldwin, B. S.↗
NASA NTRS1976

Analysis of panel dent resistance

An analytical technique for elastic-plastic deformation of panels was developed, which is employed to analyze the denting mechanisms of panels resulting from point projectile impacts and impulsive loadings. The correlations of analytical results with the experimental measurements are considered quite satisfactory. The effect of elastic springback on the dent resistance analysis is found to be very significant for the panel (122 cm x 60.9 cm x 0.076 cm) subjected to a point projectile impact at 16.45 m/sec. While the amount of springback decreases as the loading speed increases, the effect due to the strain rate hardening of material, such as low carbon steel, becomes more dominant and is demonstrated in the analysis of dent resistance of a rectangular steel plate impulsively loaded.

Ni, C. M.↗
NASA NTRS1981

Microstructure and mechanical properties of bulk yttria-partially-stabilized zirconia

A commercially available bulk 4.5 mole percent yttria-Y2O3)-partially-stabilized zirconia (PSZ) was studied by light microscopy, X-ray analysis, microhardness measurement, and fracture toughness testing. The growth of the precipitates and the phase transformations were studied as a function of aging in air at 1500 C. Aging cuves were constructed for both the as-received and the solution-annealed-and-quenched materials; the curves showed hardness peaks at 1397 and 1517 kg/sq mm, respectively. A total of twelve different types of tetragonal precipitates were found. The rectangular plate-shaped tetragonal precipitates were found to have a (110) habit plane. Grinding of the Y2O3 PSZ into powder did not cause a significant amount of metastable tetragonal precipitates to transform into the monoclinic phase, thus indicating that transformation toughening is not a significant mechanism for the material. The fracture toughness of the aged and of the unaged solution-annealed-and-quenched PSZ was found to be between 2 and 3 MN/cu m/2.

Valentine, P. G.↗
NASA NTRS1983

Designing Glass Panels for Economy and Reliability

Analytical method determines probability of failure of rectangular glass plates subjected to uniformly distributed loads such as those from wind, earthquake, snow, and deadweight. Developed as aid in design of protective glass covers for solar-cell arrays and solar collectors, method is also useful in estimating the reliability of large windows in buildings exposed to high winds and is adapted to nonlinear stress analysis of simply supported plates of any elastic material.

Moore, D. M.↗
NASA NTRS1982

Advances and trends in plate buckling research

Advances and current trends in plate bucklin research are summarized. The field is divided into three parts: (1) classical buckling studies, including plates of rectangular, circular and other shapes; (2) classical complicating effects, including elastic foundation, anisotropic material, variable thickness, shear deformation and nonhomogeneous material; and (3) nonclassical considerations, including postbuckling, imperfections, parametric excitation, follower forces, magnetoelastic buckling and inelastic buckling.

Leissa, A.↗
NASA NTRS1984

Vibrations of twisted cantilevered plates - Summary of previous and current studies

This work summarizes a comprehensive study made of the free vibrations of twisted, cantilevered plates of rectangular planform. Numerous theoretical and experimental investigations previously made by others have resulted in frequency results which disagree considerably. To clarify the problem a joint industry/government/university research effort was initiated to obtain comprehensive theoretical and experimental results for models having useful ranges of aspect ratios, thickness ratios and twist angles. Theoretical data came from 19 independent computer analyses, including finite element, shell theory and beam theory idealizations. Two independent sets of experimental data were also obtained. The theoretical and experimental results are summarized and compared.

Leissa, A. W.↗