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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1961

Theoretical Elastic Stress Distributions Arising from Discontinuities and Edge Loads in Several Shell-Type Structures

The deformation and complete stress distribution are determined for each of the following edge loaded thin shells of revolution: (1) a right circular cylinder, (2) a frustum of a right circular cone, and (3) a portion of a sphere. The locations of the maximum circumferential and meridional stresses on both the inner and outer surfaces are also found. The basic equations for the above were selected from the published literature on the subject and expanded to produce to resultant-stress equations in closed from where practicable to do so. Equations are also developed for the discontinuity shear force and bending moment at each of the following junction: (1) axial change of thickness in a circular cylinder, (2) axial change of thickness in a cone, (3) change of thickness in a portion of a sphere, (4) a cylinder and a cone, (5) a cylinder and a portion of a sphere(6) a cylinder and a flat head, and (7) a cone and a portion of a sphere.

Johns, Robert H.↗
NASA NTRS1999

Design and Development of Lightweight Composite Tanks for the Mars Ascent Propulsion Technology

The investigation presented here focuses on the design and development of lightweight composite tanks for the Mars ascent propulsion technology. The proposed tanks are fabricated using the filament winding technique. The tanks will be used in the experimental permeability characterization of composite pressure vessels pressurized using cryogenic and kerosene fluids. We considered the geometry and composite material tailorability in the preliminary design formulation to obtain an isotensoid tank. The design formulation is based on membrane shell analysis. The tanks also include circular openings at the apex of the end caps for the installation of polar bosses. The development of a polar boss system was also investigated, and led to an innovative polar boss system that applies a uniform pressure on the o-ring gaskets. The permeability of these tanks was also considered and recommendations for improvement are presented.

Estrada, Hector↗
NASA NTRS1996

Structural Concepts Study of Non-circular Fuselage Configurations

A preliminary study of structural concepts for noncircular fuselage configurations is presented. For an unconventional flying-wing type aircraft, in which the fuselage is inside the wing, multiple fuselage bays with non-circular sections need to be considered. In a conventional circular fuselage section, internal pressure is carried efficiently by a thin skin via hoop tension. If the section is non-circular, internal pressure loads also induce large bending stresses. The structure must also withstand additional bending and compression loads from aerodynamic and gravitational forces. Flat and vaulted shell structural configurations for such an unconventional, non-circular pressurized fuselage of a large flying-wing were studied. A deep honeycomb sandwich-shell and a ribbed double-wall shell construction were considered. Combinations of these structural concepts were analyzed using both analytical and simple finite element models of isolated sections for a comparative conceptual study. Weight, stress, and deflection results were compared to identify a suitable configuration for detailed analyses. The flat sandwich-shell concept was found preferable to the vaulted shell concept due to its superior buckling stiffness. Vaulted double-skin ribbed shell configurations were found to be superior due to their weight savings, load diffusion, and fail-safe features. The vaulted double-skin ribbed shell structure concept was also analyzed for an integrated wing-fuselage finite element model. Additional problem areas such as wing-fuselage junction and pressure-bearing spar were identified.

Mukhopadhyay, Vivel↗
NASA NTRS2018

Bistable Collapsible Tubular Mast Booms

A promising candidate for deployable composite structures is the two-shelled Collapsible Tubular Mast (CTM) boom, which is to be employed on future solar sail and interplanetary small satellite platforms by the National Aeronautics and Space Administration (NASA). This is due to its two omega-shaped shells forming a closed-section which yields large stiffnesses that allowed for high dimensional stability. An inextensional analytical model describing the bending deformation mechanics of CTM booms was used to determine how design variables induce bistability, or the existence of two strain energy wells. Bistable booms were favorable due to low strain energy requirements for the coiled state and had more controllable deployment when compared to monostable booms. The effects of varying lamina material, laminate layup, and shell arc geometries between different inner and outer shell segments on the second strain energy well and stiffness properties were determined for cross-sections formed by circular segments. The full design space for two-shelled composite CTM booms was explored to evaluate the validity of the simple analytical model developed. Optimal CTM boom designs were manufactured and experimentally characterized for comparisons against model results. The model under-predicted the second stable coiled diameter of the complete two-shelled booms by 27-33% and as low as 3-8% for the individual shells wrapped alone.

Fernandez, Juan M.↗
NASA NTRS1998

Compression Strength of Composite Primary Structural Components

Research conducted under NASA Grant NAG-1-537 focussed on the response and failure of advanced composite material structures for application to aircraft. Both experimental and analytical methods were utilized to study the fundamental mechanics of the response and failure of selected structural components subjected to quasi-static loads. Most of the structural components studied were thin-walled elements subject to compression, such that they exhibited buckling and postbuckling responses prior to catastrophic failure. Consequently, the analyses were geometrically nonlinear. Structural components studied were dropped-ply laminated plates, stiffener crippling, pressure pillowing of orthogonally stiffened cylindrical shells, axisymmetric response of pressure domes, and the static crush of semi-circular frames. Failure of these components motivated analytical studies on an interlaminar stress postprocessor for plate and shell finite element computer codes, and global/local modeling strategies in finite element modeling. These activities are summarized in the following section. References to literature published under the grant are listed on pages 5 to 10 by a letter followed by a number under the categories of journal publications, conference publications, presentations, and reports. These references are indicated in the text by their letter and number as a superscript.

Johnson, Eric R.↗
NASA NTRS1972

Some applications of NASTRAN to the buckling of thin cylindrical shells with cutouts

The buckling of isotropic and waffle-stiffened circular cylinders with and without cutouts was studied using NASTRAN's Rigid Format 5 for the case of axial compressive loading. The results obtained for the cylinders without cutouts are compared with available reference solutions. The results for the isotropic cylinders containing a single circular cutout with selected radii are compared with available experimental data. For the waffle-stiffened cyclinder, the effect of two diametrically opposed rectangular cutouts was studied. A DMAP alter sequence was used to permit the necessary application of different prebuckling and buckling boundary conditions. Advantage was taken of available symmetry planes to formulate equivalent NASTRAN model segments which reduced the associated computational cost of performing the analyses. Limitations of the applicability of NASTRAN for the solution of problems with nonlinear characteristics are discussed.

Williams, J. G.↗
NASA NTRS1981

Characteristics of reflected and diffuse ions upstream from the earth's bow shock

The distinction between two types of upstream ion populations is made on the basis of pronounced differences in their distribution functions. The reflected ions represent a fast beam with temperatures typically one-million to five-million K and speeds up to five times the solar wind speed. An important feature of the reflected ion distributions is their strong temperature anisotropy, with perpendicular temperature exceeding parallel temperature by a factor of two or three. In contrast, the diffuse ions occupy a much larger region of phase space, both in energy and angle; their distribution function generally has the form of a circular ridge in two dimensions and a spherical shell in three dimensions. Accordingly, their temperature is much larger (not less than about 10-million K) and their bulk speed is typically smaller than the solar wind speed.

Paschmann, G.↗
NASA NTRS1943

Some Investigations of the General Instability of Stiffened Metal Cylinders IV : Continuation of Tests of Sheet-covered Specimens and Studies of the Buckling Phenomena of Unstiffened Circular Cylinders

This is the fourth of a series of reports covering an investigation of the general instability problem by the California Institute of Technology. The first five reports of this series cover investigations of the general instability problem under the loading conditions of pure bending and were prepared under the sponsorship of the Civil Aeronautics Administration. The succeeding reports of this series cover the work done on other loading conditions under the sponsorship of the National Advisory Committee for Aeronautics. This report is to deal primarily with the continuation of tests of sheet-covered specimens and studies of the buckling phenomena of unstiffened circular cylinders.

CYLINDERS, STEEL↗
NASA NTRS1962

THE MEMBRANE APPROACH TO BENDING INSTABILITY OF PRESSURIZED CYLINDRICAL SHELLS

Recent theoretical and experimental research is briefly described to trace the development of deformation and the occurrence of collapse in pressurized circular cylindrical membranes under applied moment loading. The collapse of pure membrane cylinders is then compared with instability of pressurized cylindrical shells. This approach leads to a better understanding of the behavior of pressurized cylinders under bending loads. The results suggest possibilities for further research utilizing the membrane approach.

SHELL STABILITY↗
NASA NTRS1974

Stresses in dome-shaped shells of revolution with discontinuities at the apex

Asymptotic solutions of Novozhilov's equations of shells of revolution are derived for axisymmetric and first harmonic loadings. The solutions obtained are valid throughout the shallow and nonshallow regions. Stresses in dome shaped shells of revolution with a discontinuity in the form of a circular hole, a circular rigid insert, or a nozzle at the apex have been investigated. Numerical results are obtained for spheres, ellipsoids, and paraboloids, containing a discontinuity under a internal pressure and moment. Curves depicting stress distributions are given. The influence of three types of discontinuity on the stresses of the shells is also given.

Chen, C. H.↗
NASA NTRS1990

Eddy current heating in magnetic refrigerators

Eddy current heating can be a significant source of parasitic heating in low temperature magnetic refrigerators. To study this problem a technique to approximate the heating due to eddy currents has been developed. A formula is presented for estimating the heating within a variety of shapes commonly found in magnetic refrigerators. These shapes include circular, square, and rectangular rods; cylindrical and split cylindrical shells; wire loops; and 'coil foil. One set of components evaluated are different types of thermal radiation shields. This comparison shows that a simple split shield is almost as effective (only 23 percent more heating) as using a shield, with the same axial thermal conductivity, made of 'coil foil'.

Kittel, Peter↗
NASA NTRS2012

TPSAS-NF1676L-13555-DND

A sub-scale advanced composite shell design is evaluated to determine its potential for use on a future aircraft fuselage. Two composite shells with the same nominal 8-ply [?45/?]s layup are evaluated, where ? indicates a tow-steered ply. To build this shell, a fiber placement machine is used to steer unidirectional prepreg tows as they are placed around the circumference of a 17-inch diameter right circular cylinder. The fiber orientation angle varies continuously from 10 degrees (with respect to the shell axis of revolution) at the crown, to 45 degrees on the side, and back to 10 degrees on the keel. All 24 tows are placed at each point on every fiber path in one structure designated as the shell with overlaps. The resulting pattern of tow overlaps causes the laminate thickness to vary between 8 and 16 plies. The second shell without tow overlaps uses the capability of the fiber placement machine to cut and add tows at any point along the fiber paths to fabricate a shell with a nearly uniform 8-ply laminate thickness. Static stiffness and buckling loads of shells with tow-steered layups are compared with the performance of a baseline quasi-isotropic shell using both finite element analyses and classical strength of materials theory. These tailored, tow-steered shells were then were designed and built at the National Center for Advanced Manufacturing - Louisiana Partnership under a joint NASA-industry collaborative effort. The shells were fabricated from unidirectional IM7/8552 graphite-epoxy pre-preg slit tape material placed on a constant-diameter mandrel. An overview of the detailed design and manufacturing processes for these shells is presented, and issues encountered during their design, analysis, fabrication and post-cure evaluation are presented and discussed. Future plans for structural testing and analyses of the shells are also discussed.

K Chauncey Wu↗
NASA NTRS2008

Design and Analysis of Tow-Steered Composite Shells Using Fiber Placement

In this study, a sub-scale advanced composite shell design is evaluated to determine its potential for use on a future aircraft fuselage. Two composite shells with the same nominal 8-ply [+/-45/+/-Theta](sub s) layup are evaluated, where Theta indicates a tow-steered ply. To build this shell, a fiber placement machine would be used to steer unidirectional prepreg tows as they are placed around the circumference of a 17-inch diameter right circular cylinder. The fiber orientation angle varies continuously from 10 degrees (with respect to the shell axis of revolution) at the crown, to 45 degrees on the side, and back to 10 degrees on the keel. All 24 tows are placed at each point on every fiber path in one structure designated as the shell with overlaps. The resulting pattern of tow overlaps causes the laminate thickness to vary between 8 and 16 plies. The second shell without tow overlaps uses the capability of the fiber placement machine to cut and add tows at any point along the fiber paths to fabricate a shell with a nearly uniform 8-ply laminate thickness. Issues encountered during the design and analysis of these shells are presented and discussed. Static stiffness and buckling loads of shells with tow-steered layups are compared with the performance of a baseline quasi-isotropic shell using both finite element analyses and classical strength of materials theory.

Wu, K. Chauncey↗
NASA NTRS2012

Validation of Lower-Bound Estimates for Compression-Loaded Cylindrical Shells

The traditional approach used in the design of stability critical thin-walled circular cylin- ders, is to reduce unconservative buckling load predictions with an empirical knockdown factor. An alternative analysis-based approach to determine a lower bound buckling load for cylinders under axial compression is to use a lateral perturbation load to create an initial imperfection and determine the buckling load while that load is applied. This paper describes a preliminary e ort to develop a test capability to verify this approach. Results from tests of three aluminum alloy cylinders are described and compared to nite element predictions.

Haynie, Waddy T.↗
NASA NTRSDate not supplied

Bistable Deployable Composite Booms With Parabolic Cross-Sections

This paper investigates how stable equilibrium states in the extended and coiled configurations can be predicted in thin-shelled composite booms with parabolic cross-sections. These conic shapes potentially offer greater stiffness properties when compared to circular cross-sections, which is critical for improving the load bearing performance of deployed booms. Inducing bistability through the choice of composite shell layups in parabolic booms would allow for controllable self-deployment due to a less energetic coiled state when compared to monostable booms. An inextensional analytical model is used to predict the stable coiled diameters of tape spring and Collapsible Tubular Mast (CTM) booms with parabolic cross-sections. The parabolic section is discretized into circular segments using biarc spline interpolation, which allows them to be integrated into the strain energy minimization procedure used to obtain the equilibrium states. When the parabolic booms are parametrically compared against circular booms with identical layups, flattened height, and mass, the former are found to generally have better stiffness performance while being less efficient in stowed volume as evidenced by larger coiled diameters. Analytical coiled diameters and their strain energy are verified with finite element simulations for optimal parabolic tape spring and CTM booms.

Andrew J. Lee↗
NASA NTRS1977

An analysis of the Wheeler method for measuring the radiating efficiency of antennas

A model problem is formulated to evaluate the limitations imposed by the assumptions in the Wheeler or cap method for measuring the radiating efficiency of antennas. The antenna in the model is a circular loop and the radiation shield is a spherical metal shell. Calculated values of the actual efficiency of the antenna and the efficiency that would be measured using the Wheeler method are compared to determine the accuracy of the method and set guidelines for its application.

Smith, G. S.↗