SEARCH · Engineering Papers

Results for “buckling”

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 1,513 records · Page 84

All sources NASA NTRS DOE OSTI

NASA NTRS1983

On the dynamic response and collapse of slender guyed booms for space application

A procedure is developed for the analysis of the nonlinear transient response of an initially imperfect slender guyed boom having a concentrated mass at the tip. The analysis is compared with laboratory experiments, and the validated procedure is employed to study the transient response of a boom to suddenly applied step loads and prescribed initial velocities. Both cases approximate the transient conditions associated with commencing and terminating a slewing maneuver in space. Two nonlinear effects are examined, namely cable slackening and beam column behavior. It is shown that dynamic buckling of the boom may occur with excitations which result in slackening of a cable. It is also shown that transverse boom tip deflections are sensitive only to initial eccentricities when certain threshold values are exceeded. Design guidelines are established for combinations of pulse level and duration which meet performance requirements for allowable deflections.

Housner, J. M.↗

NASA NTRS1982

Residual stress in high modulus carbon fibers

The modulus and residual strain in carbon fibers are measured by successively electrochemically milling away the fiber surface. Electrochemical etching is found to remove the carbon fiber surface very uniformly, in contrast to air and wet oxidation. The precision of fiber diameter measurements is improved by using a laser diffraction technique instead of optical methods. More precise diameter measurements reveal that past correlations of diameter and fiber modulus are largely measurement artifact. The moduli of most carbon fibers decrease after the outer layers of the fibers are removed. Owing to experimental difficulties, the moduli and strengths of the fibers at their centers are not determined, and moduli are estimated on the basis of microstructure. The calculated residual stresses are found to be insensitive to these moduli estimates as well as the exact form of regression equation used to describe the moduli and residual strain distributions. Axial compressive residual stresses are found to be very high for some higher modulus carbon fibers. It is pointed out that the compressive stress makes the fibers insensitive to surface flaws when loaded in tension but it may initiate failure by buckling when loaded in compression.

Chen, K. J.↗

NASA NTRS1983

Stability, vibration and passive damping of partially restrained imperfect columns

A theoretical and experimental study of slender tubular columns for possible use in space structures is conducted in the presence of partial rotational end restraints. Explicit formulas are derived for computing the buckling load and the lowest natural frequency of perfectly straight uniform elastic members with rotational end restraints possessing linear moment-rotation characteristics. An exact solution in the form of a transcendental equation, and a numerical solution using second-order finite-differences are also presented. The presence of an initial imperfection is also incorporated into the numerical procedure. Vibration tests are conducted on an imperfect tubular steel member in the absence of an axial load. A damping concept consisting of a string-mass assembly is explored. Three passive damping configurations involving combinations of three lead shots were investigated. The three lead shot configurations provided considerably greater damping than the single lead shot.

Razzaq, Z.↗

NASA NTRS1984

Structural efficiency studies of corrugated compression panels with curved caps and beaded webs

Curved cross-sectional elements are employed in structural concepts for minimum-mass compression panels. Corrugated panel concepts with curved caps and beaded webs are optimized by using a nonlinear mathematical programming procedure and a rigorous buckling analysis. These panel geometries are shown to have superior structural efficiencies compared with known concepts published in the literature. Fabrication of these efficient corrugation concepts became possible by advances made in the art of superplastically forming of metals. Results of the mass optimization studies of the concepts are presented as structural efficiency charts for axial compression.

Davis, R. C.↗

NASA NTRS1984

POSTOP: Postbuckled open-stiffener optimum panels-theory and capability

The computer program POSTOP was developed to serve as an aid in the analysis and sizing of stiffened composite panels that are loaded in the postbuckling regime. A comprehensive set of analysis routines was coupled to a widely used optimization program to produce this sizing code. POSTOP is intended for the preliminary design of metal or composite panels with open-section stiffeners, subjected to multiple combined biaxial compression (or tension), shear and normal pressure load cases. Longitudinal compression, however, is assumed to be the dominant loading. Temperature, initial bow eccentricity and load eccentricity effects are included. The panel geometry is assumed to be repetitive over several bays in the longitudinal (stiffener) direction as well as in the transverse direction. Analytical routines are included to compute panel stiffnesses, strains, local and panel buckling loads, and skin/stiffener interface stresses. The resulting program is applicable to stiffened panels as commonly used in fuselage, wing, or empennage structures. The analysis procedures and rationale for the assumptions used therein are described in detail.

Dickson, J. N.↗

NASA NTRS1984

POSTOP: Postbuckled open-stiffener optimum panels, user's manual

The computer program POSTOP developed to serve as an aid in the analysis and sizing of stiffened composite panels that may be loaded in the postbuckling regime, is intended for the preliminary design of metal or composite panels with open-section stiffeners, subjected to multiple combined biaxial compression (or tension), shear and normal pressure load cases. Longitudinal compression, however, is assumed to be the dominant loading. Temperature, initial bow eccentricity and load eccentricity effects are included. The panel geometry is assumed to be repetitive over several bays in the longitudinal (stiffener) direction as well as in the transverse direction. Analytical routines are included to compute panel stiffnesses, strains, local and panel buckling loads, and skin/stiffener interface stresses. The resulting program is applicable to stiffened panels as commonly used in fuselage, wing, or empennage structures. The capabilities and limitations of the code are described. Instructions required to use the program and several example problems are included.

Biggers, S. B.↗

NASA NTRS1984

Static and dynamic structural-sensitivity derivative calculations in the finite-element-based Engineering Analysis Language (EAL) system

The implementation of static and dynamic structural-sensitivity derivative calculations in a general purpose, finite-element computer program denoted the Engineering Analysis Language (EAL) System is described. Derivatives are calculated with respect to structural parameters, specifically, member sectional properties including thicknesses, cross-sectional areas, and moments of inertia. Derivatives are obtained for displacements, stresses, vibration frequencies and mode shapes, and buckling loads and mode shapes. Three methods for calculating derivatives are implemented (analytical, semianalytical, and finite differences), and comparisons of computer time and accuracy are made. Results are presented for four examples: a swept wing, a box beam, a stiffened cylinder with a cutout, and a space radiometer-antenna truss.

Camarda, C. J.↗

NASA NTRS1984

Optimization of space structures

Computational methods for the design of structures for specified transient response, truss beam units with specified attached vibration absorbers, and laminates for structural components of large space structures are examined. Equations for the measurement of structural stiffness that are maximized for a specific total mass and that will reduce the structural weight are presented. A model for a cantilevered space truss beam of a specific mass and with a specified tip vibration absorber is explained. Design criteria of the laminates include minimizing the weight as well as frequency, buckling, and global stiffness constraints. Other variables include orientation of the lamina and the thickness of each layer.

Reiss, R.↗

NASA NTRS1983

Interply layer degradation effects on composite structural response

Recent research activities at NASA Lewis Research Center to computationally evaluate the effects of interply layer progressive weakening (degradation) on the structural response of a composite beam are summarized. The structural responses of interest include: (1) bending, (2) buckling, (3) free vibrations, (4) periodic excitation, and (5) impact. Finite element analysis was used for the computational evaluations. The interply layer degradation effects on the various structural responses were determined and assessed as a function of the interply layer modulus varying from 1 million psi down to 1000 psi and even lower for some limiting cases. The results obtained show that the interply layer degradation has generally negligible effects on composite structural response and, therefore, structural integrity, unless the interply layer modulus degrades to about 10,000 psi or less.

Chamis, C. C.↗

NASA NTRS1984

Edge Stabilized Ribbon (ESR); Stress, Dislocation Density and Electronic Performance

The edge stabilized ribbon (ESR) silicon ribbon was grown in widths of 1, 2.2 and 4.0 inches at speeds ranging from .6 to 7 in/min, which result in ribbon thicknesses of 5 to 400 microns. One of the primary problems remaining in ESR growth is that of thermally induced mechanical stresses. This problem is manifested as ribbon with a high degree of residual stress or as ribbon with buckled ribbon. Thermal stresses result in a high dislocation density in the grown material, resulting in compromised electronic performance. Improvements in ribbon flatness were accomplished by modification of the ribbon cooling profile. Ribbon flatness and other experimental observations of ESR ribbon are discussed. Laser scanner measurements show a good correlation between diffusion length and dislocation density which indicates that the high dislocation densities are the primary cause of the poor current performance of ESR materials. Dislocation densities were reduced and improved electronic performance resulted. Laser scanner data on new and old material are presented.

Sachs, E. M.↗

NASA NTRS1984

ACEE Composite Structures Technology: Review of selected NASA research on composite materials and structures

The NASA Aircraft Energy Efficiency (ACEE) Composite Primary Aircraft Structures Program was designed to develop technology for advanced composites in commercial aircraft. Research on composite materials, aircraft structures, and aircraft design is presented herein. The following parameters of composite materials were addressed: residual strength, damage tolerance, toughness, tensile strength, impact resistance, buckling, and noise transmission within composite materials structures.

Source record↗

NASA NTRS1984

Design of a composite wing extension for a general aviation aircraft

A composite wing extension was designed for a typical general aviation aircraft to improve lift curve slope, dihedral effect, and lift to drag ratio. Advanced composite materials were used in the design to evaluate their use as primary structural components in general aviation aircraft. Extensive wind tunnel tests were used to evaluate six extension shapes. The extension shape chosen as the best choice was 28 inches long with a total area of 17 square feet. Subsequent flight tests showed the wing extension's predicted aerodynamic improvements to be correct. The structural design of the wing extension consisted of a hybrid laminate carbon core with outer layers of Kevlar - layed up over a foam interior which acted as an internal support. The laminate skin of the wing extension was designed from strength requirements, and the foam core was included to prevent buckling. A joint lap was recommended to attach the wing extension to the main wing structure.

Adney, P. S.↗

NASA NTRS1984

Compression failure mechanisms in unidirectional composites

Compression failure mechanisms in unidirectional composites were examined. Possible failure modes of constituent materials are summarized and analytical models for fiber microbuckling are reviewed from a unified viewpoint. Due to deficiencies in available models, a failure model based on nonlinear properties and initial fiber curvature is proposed. The effect of constituent properties on composite compression behavior was experimentally investigated using two different graphite fibers and four different epoxy resins. The predominant microscopic scale failure mode was found to be shear crippling. In a soft resin, shear crippling was in the form of buckling of fibers on a microscopic scale. However, stiff resins failure was characterized by the formation of a kink band. For unidirectional laminates, compressive strength, and compressive modulus to a less extent, were found to increase with increasing magnitude of resin modulus. The change in compressive strength with resin modulus was predicted using the proposed nonlinear model.

Hahn, H. T.↗

NASA NTRS1984

Extensional collapse modes of structural members

Attenuation of the load transmitted to a vehicle occupant by the structure, either by modifying structural assembly, changing geometry of its elements, or adding specific load limiting devices to help dissipate kinetic energy was studied. General aviation aircraft have fuselage subfloors of a built up structure which are generally very stiff perpendicular to the floor of the cabin. The subfloor structure, designed to crush at an appropriate force level, can be used to advantage in a crash by dissipating energy through plastic buckling of the floor beams and frames. Simple closed form solutions to predict the mean crushing force levels of subfloor designs is useful in engineering practice. The crushing process of thin walled, plate formed, open structures with particular emphasis on L and cruciform shapes was analyzed. Lower and upper bound solutions for the mean crushing strength of cruciforms are obtained by considering modes of deformation which account for both bending and extensional deformation. It is the importance of extensional deformation to the energy absorption process, representing at least one third of the dissipated energy is shown. Previously announced in STAR as N82-33765

Hayduk, R. J.↗

NASA NTRS1983

Correlation of compressive and shear stress with spalling of plasma-sprayed ceramic materials

Ceramics on metal substrates for potential use as high temperature seals or other applications are exposed to forces originating from differences in thermal expansion between the ceramic and the metal substrate. This report develops a relationship between the difference in expansion of the ceramic and the substrate, defines conditions under which shear between the ceramic and the substrate occurs, and those under which bending forces are produced in the ceramic. The off-axis effect of compression forces resulting from high temperature plastic flow of the ceramic producing buckling of the ceramic is developed. Shear is associated with the edge or boundary stresses on the component while bending is associated with the distortion of an interior region. Both modes are significant in predicting life of the ceramic. Previously announced in STAR as N83-27016

Mullen, R. L.↗

NASA NTRS1984

A nonlinear structural concept for drag-reducing compliant walls

Two mechanisms of drag reduction for flow over flat plates were investigated. The first mechanism employs Bushnell's hypothesis that compliant walls produce drag reduction by interfering with the formation of the turbulent spots in a turbulent boundary layer. It is shown that the amplitudes and frequencies of compliant wall motions for drag reduction might be achieved by using slightly curved walls and the resulting large amplitude motions of snap buckling. A simple structural model of an arch is used in the analysis, and an asymptotic method is developed. The required wall motions can be obtained by using materials like mylar. In addition, the delay of transition from laminar to turbulent flow by driven walls was studied for Poiseuille channel flow. The walls are driven by a periodic traveling wave. A significant increase in the transitional Reynolds number is obtained by appropriately prescribing the wavelength and phase velocity of the wall motion. Previously developed asymptotic methods are used in the analysis. Previously announced in STAR as N83-11061

Reiss, E. L.↗

NASA NTRS1983

Compressive behavior of unidirectional fibrous composites

The longitudinal compressive behavior of unidirectional fiber composites was investigated by using the Illinois Institute of Technology Research Institute (IITRI) test method with thick and thin test specimens. The test data obtained are interpreted by means of stress/strain curves from back-to-back strain gages, examination of fracture surfaces by scanning electron microscope, and predictive equations for distinct failure modes including fiber compression failure. Euler buckling, delamination, and flexure. The results show that longitudinal compressive fracture is induced by a combination of delamination, flexure, and fiber tier breaks. No distinct fracture surface characteristics can be associated with unique failure modes. An equation is described that can be used to extract the longitudinal compressive strength from the longitudinal tensile and flexural strengths of the same composite system.

Sinclair, J. H.↗

NASA NTRS1984

Generic Karman-Rostovstev plate equations in an affine space

The Karman-Rostovstev plate equations are affinely transformed into equations that depend on the generic plate constants generalized rigidity, generalized extensional rigidity, and generalized Poisson ratio associated with the well-known linearized orthotropic plate/slab equations. Furthermore, since the generalized extensional rigidity is a function of generalized rigidity and generalized Poisson ratio only, with generalized Poisson ratio being a weak parameter, the only fundamental constant is generalized rigidity. This means that regardless of what analysis technique is used, the results can be cast in terms of only one strong material parameter (whose range is from zero to one). The affine stretching is performed on the dependent variables as well as the independent variables, so that the dependence of all quantities of interest on generalized rigidity and generalized Poisson ratio are easily calculated (e.g., even auxiliary quantities such as stress, strain, all weighted stress resultants, etc.). Some typical results (static side load response, collapse load limited by rib buckling) are presented by modifying an approximate technique due to Donnell (1976).

Brunelle, E. J.↗