SEARCH · Search NASA

Results for “PLATES - PLASTICITY”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46

All sources NASA NTRS DOE OSTI

NASA NTRS1991

Steady-state heat conduction in multilayered composite plates and shells

A study is made of a predictor-corrector procedure for the accurate determination of the temperature and heat flux distributions in thick multilayered composite plates and shells. A linear through-the-thickness temperature distribution is used in the predictor phase. The functional dependence of temperature on the thickness coordinate is then calculated a posteriori and used in the corrector phase. Extensive numerical results are presented for linear steady-state heat conduction problems, showing the effects of variation in the geometric and lamination parameters on the accuracy of the thermal response predictions of the predictor-corrector approach. Both antisymmetrically laminated anisotropic plates and multilayered orthotropic cylinders are considered. The solutions are assumed to be periodic in the surface coordinates. For each problem the standard of comparison is taken to be the analytic three-dimensional solution based on treating each layer as a homogeneous anisotropic medium. The potential of the predictor-corrector approach for predicting the thermal response of multilayered plates and shells with complicated geometry is discussed.

Noor, A. K.↗

NASA NTRS1991

Transfer function modeling of damping mechanisms in viscoelastic plates

This work formulates a method for the modeling of material damping characteristics in plates. The Sophie German equation of classical plate theory is modified to incorporate hysteresis effects represented by complex stiffness using the transfer function approach proposed by Golla and Hughes, (1985). However, this procedure is not limited to this representation. The governing characteristic equation is decoupled through separation of variables, yielding a solution similar to that of undamped classical plate theory, allowing solution of the steady state as well as the transient response problem.

Slater, J. C.↗

NASA NTRS1991

High-intensity acoustic tests of a thermally stressed plate

An investigation was conducted in the Thermal Acoustic Fatigue Apparatus at the Langley Research Center to study the acoustically excited random motion of an aluminum plate which is buckled due to thermal stresses. The thermal buckling displacements were measured and compared with theory. The general trends of the changes in resonances frequencies and random responses of the plate agree with previous theoretical prediction and experimental results for a mechanically buckled plate.

Ng, Chung Fai↗

NASA NTRS1991

Predictor-corrector procedures for thermal buckling analysis of multilayered composite plates

A study is made of two predictor-corrector procedures for the accurate determination of global, as well as detailed, thermal buckling response characteristics of composite plates. Both procedures use first-order shear deformation theory in the predictor phase, but differ in the elements of the computational model being adjusted in the corrector phase. The first procedure calculates a posteriori estimates of the composite correction factors and uses them to adjust the transverse shear stiffnesses of the plate. The second procedure calculates a posteriori the functional dependence of the displacement components on the thickness coordinate. The corrected quantities are then used in conjunction with three-dimensional equations to obtain better estimates for the different response quantities. Extensive numerical results are presented, showing the effects of variation in the geometric and lamination parameters for antisymmetrically laminated composite plates subjected to uniform temperature rise, on the accuracy of the thermal buckling response obtained by predictor-corrector procedures.

Noor, A. K.↗

NASA NTRS1991

Effect of splitter plate on unsteady flows around a body of revolution at incidence

Numerical solutions of the thin-layer approximation of the 3D Navier-Stokes equations are presented for flows around an ogive-cylinder body with and without a splitter plate. It is suggested that the presence of the splitter plate prevents the interaction between flows on either side of the symmetry plane. It is concluded that, as a result of the enforced symmetry, the antisymmetric mode of the convective instability near the apex of the body cannot be excited and, therefore, the vortices remain symmetric, staying low and parallel to the upper body surface. The antisymmetric mode of the absolute instability mechanism cannot be initiated, which suppresses the alternate shedding of vortices from the cylindrical portion of the body. High-frequency fluctuations of the shear layer are found to remain virtually unaffected by the presence of the splitter plate.

Degani, David↗

NASA NTRS1991

Neotectonic studies of northern Baja California, Mexico, with LANDSAT thematic mapper and SPOT panchromatic imagery: Partitioning of dextral and extensional strain at the Pacific-North America plate boundary

Numerous studies of active faulting in southern California indicate that the San Jacinto, Elsinore, and adjacent faults west of the San Andreas fault accommodate a significant proportion of Pacific-North America relative plate motion. Because of the complex distribution of slip, little is known about the activities of these and similar structures in northern Baja California and the southward transition to the oceanic ridge transform-fault system in the Gulf of California. SPOT and LANDSAT Thematic Mapper imagery for northern Baja California was processed to optimize discrimination of lithologic and structural features. This data was used to suggest a preliminary kinematic framework for distribution of relative plate motion between 31 and 33 degrees north, in which continental borderland tectonics play an important role in partitioning of plate motion.

Miller, M. Meghan↗

NASA NTRS1992

High-frequency techniques for RCS prediction of plate geometries

The principal-plane scattering from perfectly conducting and coated strips and rectangular plates is examined. Previous reports have detailed Geometrical Theory of Diffraction/Uniform Theory of Diffraction (GTD/UTD) solutions for these geometries. The GTD/UTD solution for the perfectly conducting plate yields monostatic radar cross section (RCS) results that are nearly identical to measurements and results obtained using the Moment Method (MM) and the Extended Physical Theory of Diffraction (EPTD). This was demonstrated in previous reports. The previous analysis is extended to bistatic cases. GTD/UTD results for the principal-plane scattering from a perfectly conducting, infinite strip are compared to MM and EPTD data. A comprehensive overview of the advantages and disadvantages of the GTD/UTD and of the EPTD and a detailed analysis of the results from both methods are provided. Several previous reports also presented preliminary discussions and results for a GTD/UTD model of the RCS of a coated, rectangular plate. Several approximations for accounting for the finite coating thickness, plane-wave incidence, and far-field observation were discussed. Here, these approximations are replaced by a revised wedge diffraction coefficient that implicitly accounts for a coating on a perfect conductor, plane-wave incidence, and far-field observation. This coefficient is computationally more efficient than the previous diffraction coefficient because the number of Maliuzhinets functions that must be calculated using numerical integration is reduced by a factor of 2. The derivation and the revised coefficient are presented in detail for the hard polarization case. Computations and experimental data are also included. The soft polarization case is currently under investigation.

Balanis, Constantine A.↗

NASA NTRS1991

Time domain scattering and radar cross section calculations for a thin, coated perfectly conducting plate

Radar cross section (RCS) calculations for flat, perfectly conducting plates are readily available through the use of conventional frequency domain techniques such as the Method of Moments (MOM). However, if the plate is covered with a dielectric material that is relatively thick in comparison with the wavelength in the material, these frequency domain techniques become increasingly difficult to apply. We present the application of the Finite Difference Time Domain (FDTD) Technique to the problem of electromagnetic scattering and RCS calculations from a thin, perfectly conducting plate that is coated with a thick layer of lossless dielectric material. Both time domain and RCS calculations are presented and disclosed.

Luebbers, Raymond J.↗

NASA NTRS1992

Solar dynamic modules for Space Station Freedom: The relationship between fine-pointing control and thermal loading of the aperture plate

Dynamic simulations of Space Station Freedom (SSF) configured with solar dynamic (SD) power modules were performed. The structure was subjected to Space Shuttle docking disturbances, while being controlled with a 'natural' vibration and tracking control approach. Three control cases were investigated for the purpose of investigating the relationship between actuator effort, SD pointing, and thermal loading on the receiver aperture plate. Transient, one-dimensional heat transfer analyses were performed to conservatively predict temperatures of the multi-layered receiver aperture plate assembly and thermal stresses in its shield layer. Results indicate that the proposed aperture plate is tolerant of concentrated flux impingement during short-lived structural disturbances. Pointing requirements may be loosened and the requirement control torques lessened from that previously specified. Downsizing and simplifying the joint drive system should result in a considerable savings mass.

Quinn, Roger D.↗

NASA NTRS1991

Time domain scattering and radar cross section calculations for a thin, coated perfectly conducting plate

Radar cross section (RCS) calculations for flat, perfectly conducting plates are readily available through the use of conventional frequency domain techniques such as the Method of Moments (MOM). However, if the plate is covered with a dielectric material that is relatively thick in comparison with the wavelength in the material, these frequency domain techniques become increasingly difficult to apply. The application is presented of the Finite Difference Time Domain (FDTD) technique to the problem of electromagnetic scattering and RCS calculations from a thin, perfectly conducting plate that is coated with a thick layer of lossless dielectric material. Both time domain and RCS calculations are presented and discussed.

Luebbers, Raymond J.↗

NASA NTRS1990

Postbuckling of stiffened composite plates under combined loading

An analysis methodology for the postbuckling behavior of laminated plates under combined in-plane normal and shear loading is presented. The plates are simply supported on their ends and elastically restrained against rotation along their longitudinal edges. Discrete thickness changes along the plate edges are included in the formulation to account for attached stiffener flanges and/or edge pad-ups. The resulting analytical approach is suitable for inclusion in a preliminary sizing procedure for longitudinally stiffened composite panels.

Kunz, Richard K.↗

NASA NTRS1991

Limit cycle oscillation of a fluttering cantilever plate

A response of a cantilever plate in high supersonic flow to a disturbance is considered. The Rayleigh-Ritz method is used to solve the nonlinear oscillation of a fluttering plate. It is found that the length-to-width ratio for a cantilever plate has a great effect on flutter amplitude of the limit cycle. For small length-to-width ratio, the dominant chordwise modes are translation and rotation. It is suggested that higher bending modes must be included to obtain an accurate prediction of the flutter onset and limit cycle oscillation. For large length-to-width ratio, significant chordwise bending is apparent in the flutter motion, with the trailing edge area having the largest motion.

Dowell, Earl↗

NASA NTRS1991

Lamb wave scattering by a surface-breaking crack in a plate

An NDE method based on finite-element representation and modal expansion has been developed for solving the scattering of Lamb waves in an elastic plate waveguide. This method is very powerful for handling discontinuities of arbitrary shape, weldments of different orientations, canted cracks, etc. The advantage of the method is that it can be used to study the scattering of Lamb waves in anisotropic elastic plates and in multilayered plates as well.

Datta, S. K.↗

NASA NTRS1991

Ultrasonic characterization of multilayered thick composite plates

Guided wave propagation in a periodically laminated plate is considered when each lamina is transversely isotropic with its symmetry axis lying in the plane of the graphite-epoxy plate. The dispersion behavior of propagation modes influences the dynamic response and can be used to ultrasonically characterize the mechanical properties of the laminated plate. It is assumed that fibers are oriented at 90 deg to one another in adjacent layers and all the laminae are of equal thickness. Results obtained are in good agreement with exact solutions of previous studies.

Karunasena, W.↗

NASA NTRS1992

Initial postbuckling response of anisotropic laminated rectangular plates

It has been shown that anisotropic plates can have unstable postbuckling behavior resulting in potential imperfection sensitivity. The present paper quantifies the degree of instability for rectangular, simply supported asymmetrically laminated plates. The analysis is based on asymptotic Koiter-type expansion of postbuckling response. The degree of postbuckling instability is quantified in terms of the reduction in load carrying capacity in the immediate postbuckling range. For graphite-epoxy plates it is found that this measure of instability is very small unless the lamination asymmetry is very pronounced.

Johnson, Eric R.↗

NASA NTRS1992

Analytical shape sensitivities and approximations of modal response of generally laminated tapered skew plates

In the present determination of the derivatives of natural frequencies and mode shapes of a generally laminated tapered skew plate, with respect to various shape parameters, springs are used to simulate the essential boundary conditions. The independent shape parameters are plate surface area, aspect ratio, taper ratio, and sweep angle. Eigenvalues and eigenvectors are approximated over the range of the variable using linear, exponential, and pseudoexponential approximation schemes, and are compared with reanalysis-obtained values. Numerical results are presented for symmetrically and unsymmetrically laminated plates.

Singhvi, Sarvesh↗

NASA NTRS1991

Composite plates impact damage - An atlas

The present volume on impact damage in composite plates presents an extensive compendium of visual and graphic data regarding a variety of material and impactor parameters. The photographs are taken with X-ray and C-scan imaging in conjunction with a dye penetrant to show matrix cracks and delaminations. Impact and static-loading tests are performed on plates of graphite-epoxy, graphite-toughened epoxy, and graphite-PEEK materials. The images are presented to yield specific visual data regarding such parameters as impactor velocity, thickness of the back ply group, impactor nose radius, and the effects of multiple delaminations. The images are grouped in eight subsets that correspond to parameters including plate length, material, and the difference in fiber orientation between adjacent ply groups. This substantial volume represents a systematic effort to study the effects of several material parameters on impact damage.

Finn, Scott R.↗

NASA NTRS1992

Accuracy of critical-temperature sensitivity coefficients predicted by multilayered composite plate theories

An assessment is made of the accuracy of the critical-temperature sensitivity coefficients of multilayered plates predicted by different modeling approaches, based on two-dimensional shear-deformation theories. The sensitivity coefficients considered measure the sensitivity of the critical temperatures to variations in different lamination and material parameters of the plate. The standard of comparison is taken to be the sensitivity coefficients obtained by the three-dimensional theory of thermoelasticity. Numerical studies are presented showing the effects of variation in the geometric and lamination parameters of the plate on the accuracy of both the sensitivity coefficients and the critical temperatures predicted by the different modeling approaches.

Noor, Ahmed K.↗