Neurophysiology
Studies in neural network stability and transition matrixes, impalement techniques for myoelectric fiber studies in cats, and method for lens fabrication by square plate deformation
MYOELECTRIC POTENTIAL↗
SEARCH · Search NASA
Results for “PLATE THEORY”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Flexural models of trench/outer rise topography of coronae on Venus with axisymmetric spherical shell elastic plates
Magellan altimetry has revealed that many coronae on Venus have trenches or moats around their peripheries and rises outboard of the trenches. This trench/outer rise topographic signature is generally associated with the tectonic annulus of the corona. Sandwell and Schubert have interpreted the trench/outer rise topography and the associated tectonic annulus around coronae to be the result of elastic bending of the Venus lithosphere (though the tectonic structures are consequences of inelastic deformation of the lithosphere). They used two-dimensional elastic plate flexure theory to fit topographic profiles across a number of large coronae and inferred elastic lithosphere thicknesses between about 15 and 40 km, similar to inferred values of elastic thickness for the Earth's lithosphere at subduction zones around the Pacific Ocean. Here, we report the results of using axisymmetric elastic flexure theory for the deformation of thin spherical shell plates to interpret the trench/outer rise topography of the large coronae modeled by Sandwell and Schubert and of coronae as small as 250 km in diameter. In the case of a corona only a few hundred kilometers in diameter, the model accounts for the small planform radius of the moat and the nonradial orientation of altimetric traces across the corona. By fitting the flexural topography of coronae we determine the elastic thickness and loading necessary to account for the observed flexure. We calculate the associated bending moment and determine whether the corona interior topographic load can provide the required moment. We also calculate surface stresses and compare the stress distribution with the location of annular tectonic features.
Moore, W.↗
A small-deflection theory for curved sandwich plates
Explore the source record for details and available documents.
Stein, Manuel↗
Theoretical analysis of impact in composite plates
The calculated stresses and displacements induced anisotropic plates by short duration impact forces are presented. The theoretical model attempts to model the response of fiber composite turbine fan blades to impact by foreign objects such as stones and hailstones. In this model the determination of the impact force uses the Hertz impact theory. The plate response treats the laminated blade as an equivalent anisotropic material using a form of Mindlin's theory for crystal plates. The analysis makes use of a computational tool called the fast Fourier transform. Results are presented in the form of stress contour plots in the plane of the plate for various times after impact. Examination of the maximum stresses due to impact versus ply layup angle reveals that the + or - 15 deg layup angle gives lower flexural stresses than 0 deg, + or - 30 deg and + or - 45 deg. cases.
Moon, F. C.↗
Plastic buckling
The present article is concerned mainly with the post-bifurcation and imperfection-sensitivity aspects of plastic buckling. A simple two-degree-of-freedom model is used to introduce post-bifurcation behavior and a second model illustrates features of the behavior of continuous solids and structures. Hill's bifurcation criterion for a class of three-dimensional solids is applied to the Donnell-Mushtari-Vlasov (DMV) theory of plates and shells. A general treatment of the initial post-bifurcation behavior of plates and shells is given within the context of the DMV theory. This is illustrated by problems involving columns and circular plates under radial compression. Numerical results are given for a column under axial compression, a circular plate under radial compression, and spherical and cylindrical shells.
Hutchinson, J. W.↗
Flutter of laminated plates in supersonic flow
A solution procedure was developed using linear small deflection theory for the flutter of simply supported laminated plates. For such plates, the bending and extensional governing equations are coupled and have cross-stiffness terms which do not appear in classical plate theory. An extended Galerkin method is used to obtain approximate solutions to the governing equations, and the aerodynamic pressure loading used in the analysis is that given by linear piston theory with flow at arbitrary cross-flow angle. A limited parametric study was conducted for typical laminated composite plates. The calculations show that both the bending-extensional coupling and the cross-stiffness terms have a large destabilizing effect on flutter. Since classical plate theory does not consider bending-extensional coupling and cross stiffness terms, it usually gives inaccurate and nonconservative flutter boundaries for laminated plates.
Sawyer, J. W.↗
Analysis of symmetric cross-ply laminated elastic plates using a higher-order theory. I - Stress and displacement
A simple theory for bending of composite anisotropic plates that are laminated symmetrically about their mid-plane is presented. This theory incorporates transverse shear deformation and transverse normal stress as well as the higher-order effects and fulfills the static conditions on the external boundary planes. Further on, by using Levy-type solutions considered in conjunction with the state space concept, the state of stress and displacement of rectangular plates for a variety of edge conditions is determined and the results are compared to their first-order shear deformation and classical counterparts, obtained by using the same state-space technique.
Librescu, L.↗
A Multi-scale Refined Zigzag Theory for Multilayered Composite and Sandwich Plates with Improved Transverse Shear Stresses
The Refined Zigzag Theory (RZT) enables accurate predictions of the in-plane displacements, strains, and stresses. The transverse shear stresses obtained from constitutive equations are layer-wise constant. Although these transverse shear stresses are generally accurate in the average, layer-wise sense, they are nevertheless discontinuous at layer interfaces, and thus they violate the requisite interlaminar continuity of transverse stresses. Recently, Tessler applied Reissner's mixed variational theorem and RZT kinematic assumptions to derive an accurate and efficient shear-deformation theory for homogeneous, laminated composite, and sandwich beams, called RZT(m), where "m" stands for "mixed". Herein, the RZT(m) for beams is extended to plate analysis, where two alternative assumptions for the transverse shear stresses field are examined: the first follows Tessler's formulation, whereas the second is based on Murakami's polynomial approach. Results for elasto-static simply supported and cantilever plates demonstrate that Tessler's formulation results in a powerful and efficient structural theory that is well-suited for the analysis of multilayered composite and sandwich panels.
Iurlaro, Luigi↗
Theory and performance of flat plate solar thermoelectric generator for near-earth orbits.
Flat plate solar thermoelectric generator for near-Earth orbits discussing theory, design, fabrication and testing
PHOTOVOLTAIC CELL↗
Crack problems in cylindrical and spherical shells
Standard plate or shell theories were used as a starting point to study the fracture problems in thin-walled cylindrical and spherical shells, assuming that the plane of the crack is perpendicular to the surface of the sheet. Since recent studies have shown that local shell curvatures may have a rather considerable effect on the stress intensity factor, the crack problem was considered in conjunction with a shell rather than a plate theory. The material was assumed to be isotropic and homogeneous, so that approximate solutions may be obtained by approximating the local shell crack geometry with an ideal shell which has a solution, namely a spherical shell with a meridional crack, a cylindrical shell with a circumferential crack, or a cylindrical shell with an axial crack. A method of solution for the specially orthotropic shells containing a crack was described; symmetric and skew-symmetric problems are considered in cylindrical shells with an axial crack.
Erdogan, F.↗
Nonlinear oscillations of a fluttering plate.
Two- and three-dimensional plates in high supersonic flow undergoing limit cycle oscillations analyzed, using aerodynamic theory and von Karman large deflection plate theory
PLATE THEORY↗
Advances in the modeling of laminated plates
The present evaluation of extant 2D theories and computational models of laminated composite plates gives attention to the classical, as well as to various shear-deformation, plate theories. A generalization of advanced theories is proposed, and computational aspects of the displacement finite-element models of these advanced theories are discussed. The 4MREDNC-R element appears to be ideally suited to use as a flat, four-noded shell element for applications in which the bending and membrane couplings are not significant.
Reddy, J. N.↗
Efficient finite element modeling of laminated composite plates based on higher-order theory
A simple and efficient three-node plate bending element for the analysis of composite laminates is developed from a variational principle. The deformations due to transverse shear and transverse normal effects are accounted for, allowing accurate predictions in the range of thin to thick plates. The methodology incorporates C(exp 0) and C(exp 1) continuous displacement approximations and yields accurate ply-by-ply predictions of all displacement, strain, and stress variables.
Tessler, Alexander↗
Development of Curved-Plate Elements for the Exact Buckling Analysis of Composite Plate Assemblies Including Transverse Shear Effects
The analytical formulation of curved-plate non-linear equilibrium equations that include transverse-shear-deformation effects is presented. A unified set of non-linear strains that contains terms from both physical and tensorial strain measures is used. Using several simplifying assumptions, linearized, stability equations are derived that describe the response of the plate just after bifurcation buckling occurs. These equations are then modified to allow the plate reference surface to be located a distance z(c), from the centroid surface which is convenient for modeling stiffened-plate assemblies. The implementation of the new theory into the VICONOPT buckling and vibration analysis and optimum design program code is described. Either classical plate theory (CPT) or first-order shear-deformation plate theory (SDPT) may be selected in VICONOPT. Comparisons of numerical results for several example problems with different loading states are made. Results from the new curved-plate analysis compare well with closed-form solution results and with results from known example problems in the literature. Finally, a design-optimization study of two different cylindrical shells subject to uniform axial compression is presented.
McGowan, David M.↗
Flutter and buckling of general laminated plates
An anisotropic buckling and flutter analysis is developed with allowance for both bending-extensional coupling and bending-twisting coupling within the framework of linear small deflection theory for simply supported general laminated plates. The extended Galerkin method is used to obtain approximate solutions to the coupled governing equations. The effects of various anisotropic stiffness parameters on the static and dynamic stability of laminated plates are evaluated, with particular emphasis on assessing the range of applicability of classical orthotropic plate theory. It is shown that bending-extensional coupling and bending-twisting stiffness terms have a destabilizing effect on buckling and flutter, the effect being more pronounced for a small number of layers. For symmetric plates, the number of layers required for orthotropic plate theory to be applicable is generally less for the buckling problem than for flutter. For square plates, aligning the fibers with the direction of airflow over the plate surface results in the highest flutter dynamic pressure.
Sawyer, J. W.↗
Random vibrations of laminated plates modeled within the first order shear deformation theory
This paper deals with the dynamic response of anisotropic laminated composite plates to stationary random excitation. The theory of laminated plates used here includes shear deformation and rotary inertia effects in the same manner as Mindlin's theory for isotropic homogeneous plates. Two cases of random pressure fields are considered in this analysis. In the first case, it is modeled as a uniformly distributed load, random in time with an exponential decaying correlation function, while in the second one as a jet noise, fully correlated in one direction and homogeneous in the perpendicular one. The analysis presented herein, as well as the obtained response characteristics, expressed in terms of mean-squares and angle-dependent mean-squares, may be useful in the design of composite plates subjected to random pressure fields and in the evaluation of their reliability.
Cederbaum, G.↗
Analysis of laminated composite plates using a higher-order shear deformation theory
A higher-order deformation theory is used to analyse laminated anisotropic composite plates for deflections, stresses, natural frequencies and buckling loads. The theory accounts for parabolic distribution of the transverse shear stresses, and requires no shear correction coefficients. A displacement finite element model of the theory is developed, and applications of the element to bending, vibration and stability of laminated plates are discussed. The present solutions are compared with those obtained using the classical plate theory and the three-dimensional elasticity theory.
Phan, N. D.↗