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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Elastic Buckling of Laminated Plates Under Varying Axial Stresses

The elastic buckling load of simply supported rectangular composite plates subjected to a second degree parabolic variation of axial stresses in the longitudinal direction is calculated using analytical methods. The variation of axial stresses is equilibrated by nonuniform shear stresses along the plate edges and transverse normal stresses. Numerical results are reported for three different cases: (1) orthotropic plates, (2) symmetrically laminated plates with multiple generally orthotropic layers exhibiting coupling between normal moments and twist, and twisting moment and normal curvatures, and (3) unsymmetrically laminated plates. Rayleigh-Ritz method is used to calculate the buckling load. An approximate solution using "reduced bending stiffness" is adopted for unsymmetrically laminated plates. The influence of the aspect ratio is examined, and the results are compared with plates subjected to uniform axial stresses.

Badir, A.↗
NASA NTRS1986

Buckling behavior of compression-loaded symmetrically-laminated angle-ply plates with holes

An approximate analysis for buckling of a rectangular specially-orthotropic plate with a central circular hole is applied to symmetrically-laminated angle-ply plates. Results obtained from finite element analyses and experiments indicate that the approximate analysis predicts accurately the buckling loads of (+/-theta sub m)s plates with integer values of m not below 6 and with hole diameters up to 50 percent of the plate width. Moreover, the results indicate that the approximate analysis can be used to predict the buckling trends of plates with hole diameters up to 70 percent of the plate width. Results of a parametric study indicate the influence of hole size, plate aspect ratio, loading conditions, boundary conditions, and orthotropy on the buckling load. Results are also presented that indicate the relationship of the bending stiffness and the prebuckling load distribution to the buckling load of a plate with a hole.

Nemeth, M. P.↗
NASA NTRS1987

Buckling Analysis of Rectangular Plates With Holes

BUCKO is computer program developed to predict buckling of rectangular compression-loaded orthotropic plate with centrally located cutout. Plate assumed balanced, symmetric laminate of uniform thickness. Cutout shape elliptical, circular, rectangular, or square. Package includes sample data demonstrating essence of program and ease of use. Written in FORTRAN V.

Nemeth, M. P.↗
NASA NTRS1976

Symmetries in laminated composite plates

The different types of symmetry exhibited by laminated anisotropic fibrous composite plates are identified and contrasted with the symmetries of isotropic and homogeneous orthotropic plates. The effects of variations in the fiber orientation and the stacking sequence of the layers on the symmetries exhibited by composite plates are discussed. Both the linear and geometrically nonlinear responses of the plates are considered. A simple procedure is presented for exploiting the symmetries in the finite element analysis. Examples are given of square, skew and polygonal plates where use of symmetry concepts can significantly reduce the scope and cost of analysis.

Noor, A. K.↗
NASA NTRS1951

A small-deflection theory for curved sandwich plates

A small-deflection theory that takes into account deformations due to transverse shear is presented for the elastic-behavior analysis of orthotropic plates of constant cylindrical curvature, with consideration of buckling included. The theory is applicable primarily to sandwich construction. (author)

Stein, Manuel↗
NASA NTRS1990

Buckling and postbuckling behavior of square compression-loaded graphite-epoxy plates with circular cutouts

An experimental study of the postbuckling behavior of square compression-loaded graphite-epoxy plates and isotropic plates with a central circular cutout is presented. Results are presented for unidirectional (0 sub 10)s and (90 sub 10)s plates, (0/90 sub 5)s plates, and for aluminum plates. Results are also presented for (+ or - O sub 6)s angle-ply plates for values of O = 30, 46, and 60 degrees. The experimental results indicate that the change in axial stiffness of a plate at buckling is strongly dependent upon cutout size and plate orthotropy. The presence of a cutout gives rise to an internal load distribution that changes, sometimes dramtically, as a function of cutout size coupled with the plate orthotropy. In the buckled state, the role of orthotropy becomes more significant since bending in addition to membrane orthotropy is present. Most of the plates with cutouts exhibited less postbuckling stiffness than the corresponding plate without a cutout, and the postbuckling stiffness decreased with increasing cutout size. However, some of the highly orthotropic plates with cutouts exhibited more postbuckling stiffness than the corresponding plate without a cutout.

Nemeth, Michael P.↗
NASA NTRS1990

Buckling and postbuckling behavior of square compression-loaded graphite-epoxy plates with circular cutouts

Results are presented for unidirectional (0, 10)(sub s) and (90,10)(sub s) plates, ((0/90)(sub 5)(sub s)) plates, and for aluminum plates. Results are also presented for ((+/- theta)(sub 6)(sub s)) angle-ply plates for values of theta = 30, 45, and 60 degrees. The results indicate that the change in axial stiffness of a plate at buckling is strongly dependent upon cutout size and plate orthotropy. The presence of a cutout gives rise to an internal load distribution that changes, sometimes dramatically, as a function of cutout size coupled with the plate orthotropy. In the buckled state, the role of orthotropy becomes more significant since bending in addition to membrane orthotropy is present. Most of the plates with cutouts exhibited less postbuckling stiffness than the corresponding plate without a cutout, and the postbuckling stiffness decreased with increasing cutout size. However, some of the highly orthotropic plates with cutouts exhibited more postbuckling stiffness than the corresponding plate without a cutout. These results suggest the possibility of tailoring the cutout size and the stacking sequence of a composite plate to optimize postbuckling stiffness. It was found that plates with large radius cutouts do exhibit some postbuckling strength. The results also indicate that a cutout can influence modal interaction in a plate. Specifically, results are presented that show a plate with a relatively small cutout buckling at a higher load than the corresponding plate without a cutout, due to modal interaction. Other results are presented that indicate the presence of nonlinear prebuckling deformations, due to material nonlinearity, in the angle-ply plates with theta = 45 and 60 degrees. The nonlinear prebuckling deformations are more pronounced in the plates with theta = 45 degrees and become even more pronounced as the cutout size increases. Results are also presented that show how load-path eccentricity due to improper machining of the test specimens affects the buckling behavior. Some of the plates with cutouts and eccentricity exhibited a snap-through type of buckling behavior.

Nemeth, Michael P.↗
NASA NTRS1989

EAC: A program for the error analysis of STAGS results for plates

A computer code is now available for estimating the error in results from the STAGS finite element code for a shell unit consisting of a rectangular orthotropic plate. This memorandum contains basic information about the computer code EAC (Error Analysis and Correction) and describes the connection between the input data for the STAGS shell units and the input data necessary to run the error analysis code. The STAGS code returns a set of nodal displacements and a discrete set of stress resultants; the EAC code returns a continuous solution for displacements and stress resultants. The continuous solution is defined by a set of generalized coordinates computed in EAC. The theory and the assumptions that determine the continuous solution are also outlined in this memorandum. An example of application of the code is presented and instructions on its usage on the Cyber and the VAX machines have been provided.

Sistla, Rajaram↗
NASA NTRS2007

Bounds on Flexural Properties and Buckling Response for Symmetrically Laminated Plates

Nondimensional parameters and equations governing the buckling behavior of rectangular symmetrically laminated plates are presented that can be used to represent the buckling resistance, for plates made of all known structural materials, in a very general, insightful, and encompassing manner. In addition, these parameters can be used to assess the degree of plate orthotropy, to assess the importance of anisotropy that couples bending and twisting deformations, and to characterize quasi-isotropic laminates quantitatively. Bounds for these nondimensional parameters are also presented that are based on thermodynamics and practical laminate construction considerations. These bounds provides insight into potential gains in buckling resistance through laminate tailoring and composite-material development. As an illustration of this point, upper bounds on the buckling resistance of long rectangular orthotropic plates with simply supported or clamped edges and subjected to uniform axial compression, uniform shear, or pure inplane bending loads are presented. The results indicate that the maximum gain in buckling resistance for tailored orthotropic laminates, with respect to the corresponding isotropic plate, is in the range of 26-36% for plates with simply supported edges, irrespective of the loading conditions. For the plates with clamped edges, the corresponding gains in buckling resistance are in the range of 9-12% for plates subjected to compression or pure inplane bending loads and potentially up to 30% for plates subjected to shear loads.

Weaver, Paul M.↗
NASA NTRS1987

Convergence of strain energy release rate components for edge-delaminated composite laminates

Strain energy release rates for edge delaminated composite laminates were obtained using quasi 3 dimensional finite element analysis. The problem of edge delamination at the -35/90 interfaces of an 8-ply composite laminate subjected to uniform axial strain was studied. The individual components of the strain energy release rates did not show convergence as the delamination tip elements were made smaller. In contrast, the total strain energy release rate converged and remained unchanged as the delamination tip elements were made smaller and agreed with that calculated using a classical laminated plate theory. The studies of the near field solutions for a delamination at an interface between two dissimilar isotropic or orthotropic plates showed that the imaginary part of the singularity is the cause of the nonconvergent behavior of the individual components. To evaluate the accuracy of the results, an 8-ply laminate with the delamination modeled in a thin resin layer, that exists between the -35 and 90 plies, was analyzed. Because the delamination exists in a homogeneous isotropic material, the oscillatory component of the singularity vanishes.

Raju, I. S.↗
NASA NTRS1988

Convergence of strain energy release rate components for edge-delaminated composite laminates

Strain energy release rates for edge delaminated composite laminates were obtained using quasi 3 dimensional finite element analysis. The problem of edge delamination at the -35/90 interfaces of an 8-ply composite laminate subjected to uniform axial strain was studied. The individual components of the strain energy release rates did not show convergence as the delamination tip elements were made smaller. In contrast, the total strain energy release rate converged and remained unchanged as the delamination tip elements were made smaller and agreed with that calculated using a classical laminated plate theory. The studies of the near field solutions for a delamination at an interface between two dissimilar isotropic or orthotropic plates showed that the imaginary part of the singularity is the cause of the nonconvergent behavior of the individual components. To evaluate the accuracy of the results, an 8-ply laminate with the delamination modeled in a thin resin layer, that exists between the -35 and 90 plies, was analyzed. Because the delamination exists in a homogeneous isotropic material, the oscillatory component of the singularity vanishes.

Raju, I. S.↗
NASA NTRS1975

Flutter analysis of two parallel elastically coupled flat plates

Flutter of two parallel elastically coupled flat plates was investigated analytically. A closed-form solution including both aerodynamic and structural damping is presented for flutter of flat orthotropic plates coupled by an elastic medium. Both plates are simply supported along the side edges but are supported by deflectional, rotational, and torsional springs of arbitrary stiffness at the leading and trailing edges. Two-dimensional quasi-steady aerodynamics was utilized in the solution. Since the large number of variables present in the problem precludes extensive parametric studies, results are presented to indicate the basic flutter characteristics of coupled two-plate systems and to assess the validity of previously published modal solutions for similar problems.

Shore, C. P.↗
NASA NTRS1989

Dynamic stability of unidirectional fiber-reinforced viscoelastic composite plates

This paper deals with a dynamic stability analysis of unidirectional fiber-reinforced composite viscoelastic plates subjected to compressive edge loads. The integrodifferential equations governing the stability problem are obtained by using, in conjunction with a Boltzmann hereditary constitutive law for a three-dimensional viscoelastic medium, a higher-order shear deformation theory of orthotropic plates. Such a theory incorporates transverse shear deformation, transverse normal stress, and rotatory inertia effects. The solution of the stability problem as considered within this paper concerns the determination of the critical in-plane edge loads yielding the asymptotic instability. Numerical applications, based on material properties derived within the framework of Aboudi's micromechanical model, are presented and pertinent conclusions concerning the nature of the loss of stability and the influence of various parameters are outlined.

Chandiramani, N. K.↗
NASA NTRS1995

Buckling behavior of long anisotropic plates subjected to combined loads

A parametric study is presented of the buckling behavior of infinitely long symmetrically laminated anisotropic plates subjected to combined loads. The study focuses on the interaction of a subcritical (stable) secondary loading state of constant magnitude and a primary destabilizing load that is increased in magnitude until buckling occurs. The loads, considered in this report are uniform axial compression, pure in-plane bending, transverse tension and compression, and shear. Results are presented that were obtained by using a special purpose nondimensional analysis that is well suited for parametric studies of clamped and simply supported plates. In particular, results are presented for a +/- 45(sub S) graphite-epoxy laminate that is highly anisotropic and representative of a laminate used for spacecraft applications. In addition, generic buckling-design charts are presented for a wide range of nondimensional parameters that are applicable to a broad class of laminate constructions. These results show the general behavioral trends of specially orthotropic plates and the effects of flexural anisotropy on plates subjected to various combined loading conditions. An important finding of the present study is that the effects of flexural anisotropy on the buckling resistance of a plate can be significantly more important for plates subjected to combined loads than for plates subjected to single-component loads.

Nemeth, Michael P.↗
NASA NTRS1975

The effect of bending on the stresses in adhesive joints

The problem of stress distribution in adhesive joints where two orthotropic plates are bonded through a flexible adhesive layer is analyzed. It is shown that the effect of bending of the adherends on the stresses in the adhesive layer is very significant. The transverse shear deformations of the adherends appear to have little influence on the adhesive layer stresses. The maximum transverse normal stress in the adhesive is shown to be larger than the maximum longitudinal shear stress. The method of solution is applied to several examples of specific joint geometries and material combinations, and is proven to be applicable to other related problems.

Yuceoglu, U.↗