SEARCH · Engineering Papers
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.
Structures Research Associates (SRA) system of programs is composed of six compatible computer programs for structural analyses of axisymmetric shell structures. Theories and methods upon which these programs are based are presented in documentation. They apply to a common structural model but analyze different modes of structural response.
Package of numerical integration programs static, buckling, vibration, and plastic analysis on thin sheels of revolution. Sheels may be subjected to distributed loads, concentrated line loads, and thermal strain. Outputs include stresses, displacement, plastic strains, and vibration and buckling results. Program aids design of aircraft bodies, spacecraft, submarines, and storage tanks. Written in FORTRAN IV for batch execution, program has been implemented on UNIVAC 1108.
A computational method for the simulation of damage and fracture propagation in laminated composites is presented. A quantitative evaluation of the global fracture toughness of composites is shown as a tool for monitoring the fracture stability of composites under sustained loading. Changes in overall structural properties such as natural frequencies and the fundamental buckling load are also computed with increasing load-induced damage. Structural degradation, delamination, fracture, and damage propagation are included in the simulation. An angle-plied composite plate structure subjected to inplane tensile loading is used as an example to demonstrate some of the feature of the computational method.
Euler buckling is a common failure mode for long, slender structures. This demonstration presents an overview of the history of Euler buckling, sample calculations, and test results. Applications for NASA launch vehicles are presented and discussed.
The buckling characteristics of Rene 41 tubular panels installed as wing panels on a hypersonic wing test structure (HWTS) were determined nondestructively through use of a force/stiffness technique. The nondestructive buckling tests were carried out under different combined load conditions and different temperature environments. Two panels were subsequently tested to buckling failure in a universal tension compression testing machine. In spite of some data scattering because of large extrapolations of data points resulting from termination of the test at a somewhat low applied load, the overall test data correlated fairly well with theoretically predicted buckling interaction curves. The structural efficiency of the tubular panels was slightly higher than that of the beaded panels which they replaced.
Ultra-low mass deployable and erectable truss structure designs for spacecraft are identified using computerized structural sizing techniques. Extremely slender strut proportions are shown to characterize minimum mass spacecraft which are designed for shuttle transport to orbit. Discrete element effects using a recently developed buckling theory for periodic lattice type structures are presented. An analysis of fabrication imperfection effects on the surface accuracy of four different antenna reflector structures is summarized. The tetrahedral truss has the greatest potential of the structures examined for application to accurate or large reflectors. A deployable module which can be efficiently transported is identified and shown to have significant potential for application to future antenna requirements. Investigations of erectable structure assembly are reviewed.
Dynamic buckling of imperfection sensitive models, specifically cylindrical shells under axial compression
Nonlinear structural analysis of stress and buckling pressures of aft heat shield of Apollo spacecraft
Flutter design charts for isotropic panels stressed to verge of buckling for typical values of structural damping
Flutter design charts for isotropic panels stressed to verge of buckling for tropical values of structural damping
An elastic plate model is used to describe the origin of intermediate and deep earthquakes. It is shown that the earth is covered by about eight tectonic plates that have relative motions; along plate boundary lines, one plate thrusting under the other, causes deflection and buckling of the elastic plate structure in regions of maximum curvature that may trigger earthquakes.
A cylindrical finite element suitable for the linear stability analysis of cylindrical shells is developed. Energy principles and variational methods lead to a problem formulation which lends itself to physical interpretations of the governing matrices of the finite element. By properly grouping the terms which result from taking the second variation of the potential energy of the element, it is possible to identify three distinct types of matrices. The first matrix is the conventional stiffness matrix; the second is an initial stress stiffness matrix; and the third is an initial displacement stiffness matrix. With the assumption of linearity, the buckling problem is stated in terms of the classical linear real eigenvalue equation. This problem formulation was programmed on the CDC 6600 series computer. The computer program is used to analyze the buckling of a variety of structures. Columns, arches, flat plates and curved panels with and without cutouts are considered.
The turbine hot-section technology (HOST) Instrumentation R&D program focuses on two main classes of instrumentation: (1) those that characterizes the environment around the turbine engine components, which include gas flows measurement, gas temperatures, and heat fluxes; (2) to characterize the effect of the environment on the turbine engine components, which include strain measurements and an optical system to structural responses such as cracking, buckling, spalling, carbon buildup. The HOST Instrumentation R&D program concentrates on the critical measurements that can not be made by commercially available instruments or with instruments that are already in development. The measurements of strain and gas flow are emphasized, these measurements are extremely critical to the success of the HOST program and the HOST requirements differ from the current state of the art by a considerable margin.
A new, slim-profiled, low-blockage quadripod structure was designed to support the 7.7-m-diameter subreflector for the 70-m antenna. Detailed analyses of quadripod structural stability (in frequency and buckling) are presented. The results indicate that the new quadripod design has an adequate safety margin for buckling, and its lowest natural frequency is above the control system bandwidth. The analytical design frequencies were confirmed by actual field measurements made in Spain in February 1986.
The final report on the nature and origin of periodically spaced tectonic features on Mars is presented. The focus of this investigation was to characterize and model the periodically spaced wrinkle ridges observed in ridged plains material on Mars. The investigation centered on the wrinkle ridges in ridged plains material on the Tharsis Plateau. Wrinkle ridges are interpreted to be structural in origin, resulting from buckling followed by reverse or thrust faulting of the ridged plains material. The study extended beyond Tharsis to other ridged plains units, particularly those in Hesperia Planum. As a corollary, an analysis of the spacing of the anticlinal ridges of the Yakima Fold Belt of the Columbia Plateau in the NW United States was undertaken.
The accuracy of the solutions obtained with the Level-1 computational modules of DISDECO (Delft Interactive Shell Design Code) are investigated by comparing them with solutions obtained with ANILISA, a Level-2 computational module. Whereas the Level-1 solutions are based on the use of trigonometric functions to represent the out-of-plane displacement W and involve Galerkin type approximations to reduce the governing partial differential equations to simple algebraic expressions, the Level-2 solutions employ a truncated Fourier expansion in the circumferential direction and solve the resulting ordinary differential equations forming a nonlinear eigenvalue problem by a Stodola like technique. This involves the numerical integration of the set of ordinary differential equations, which in turn makes it possible to satisfy the specified boundary conditions exactly. It is shown that in many applications the Level-1 predictions concerning the critical buckling load of the perfect structure and its imperfection sensitivity are quite accurate and reliable. For those cases where this is not true, it is shown how the pre and postprocessing facilities of DISDECO can be used efficiently to arrive at a reliable prediction. This involves always the use of the Level-2 computational module ANILISA with its rigorous prebuckling solution and its feature which makes it possible to satisfy the specified boundary conditions exactly.
This paper presents the first results in an assessment of the strength, stiffness, and damage tolerance of stiffened wing and fuselage subcomponents. Under this NASA funded program, 10 large wing and fuselage panels, variously fabricated by automated tow placement and dry-stitched preform/resin transfer molding, are to be tested. The first test of an automated tow placement six-longeron fuselage panel under shear load was completed successfully. Using NASTRAN finite-element analysis the stiffness of the panel in the linear range prior to buckling was predicted within 3.5 percent. A nonlinear analysis predicted the buckling load within 10 percent and final failure load within 6 percent. The first test of a resin transfer molding six-stringer wing panel under compression was also completed. The panel failed unexpectedly in buckling because of inadequate supporting structure. The average strain was 0.43 percent with a line load of 20.3 kips per inch of width. This strain still exceeds the design allowable strains. Also, the stringers did not debond before failure, which is in contrast to the general behavior of unstitched panels.
A summary of existing NASA design criteria monographs for the design of buckling-resistant thin-shell structures is presented. Subsequent improvements in the analysis for nonlinear shell response are reviewed, and current issues in shell stability analysis are discussed. Examples of nonlinear shell responses that are not included in the existing shell design monographs are presented, and an approach for including reliability based analysis procedures in the shell design process is discussed. Suggestions for conducting future shell experiments are presented, and proposed improvements to the NASA shell design criteria monographs are discussed.