Post-buckling analyses of variable-stiffness composite cylinders in axial compression

Performance projections for aerocapture show a vehicle mass savings of between 40 and 80%, dependent on destination, for an aerocapture vehicle compared to an all-propulsive chemical vehicle. In addition aerocapture is applicable to multiple planetary exploration destinations of interest to the NASA Office of Space Science. These results led to the identification of aerocapture as one of the top three propulsion technologies for solar system exploration missions during the 2001 NASA In-Space Propulsion Program (ISP) technology prioritization effort, led by Marshall Space Flight Center, to rank current ISP propulsion technologies. An additional finding was that aerocapture needed a better system definition and that supporting technology gaps needed to be identified.

Titan Aerocapture Systems Analysis

* Senior Research Scientist, Reacting Flow Environments Branch. Senior Member AIAA  Senior Research Scientist. Senior Member AIAA  Senior Research Scientist. Associate Fellow AIAA § Senior Research Scientist. Senior Member AIAA ** Research Scientist, Aerothermodynamics Branch. Senior Member AIAA  Research Scientist, Aerothermodynamics Branch. Fellow AIAA  Research Scientist, Aerothermodynamics Branch. Fellow AIAA Copyright © 2003 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes Abstract Details of the radiative heating analysis for the forebody of a candidate Titan aerocapture orbiter are presented. The radiative heating rates are obtained through a posteriori analysis of high-fidelity thermochemical nonequilibrium flow fields computed using modern techniques of computational fluid dynamics. Results from axisymmetric and three-dimensional analysis are presented at several points on candidate aerocapture trajectories in various model atmospheres of Titan. The radiative heating rates are found to be up to five times the peak convective heating rates, indicating that an accurate knowledge of the uncertainty of the radiative heating predictions is critical for a Titan aerocapture mission. The results also show that  (1) the radiative heating rates are dominated by the violet band system of CN, and (2) the gas mixture is optically thin. The predicted radiative heating is found to be very sensitive to the dissociation rate of molecular nitrogen  a factor of two increase in the rate, which is within the experimental uncertainty, results in a 25% decrease in the radiative heating.

An Analysis of the Radiative Heating Environment for Aerocapture at Titan

Large deflection inelastic analysis of space trusses using generalized displacement control method

Buckling optimization of composite cylinders for axial compression: A design methodology considering a variable-axial fiber layout

The structural performance of two advanced composite tow-steered shells, manufactured using a fiber placement system, is assessed using both experimental and analytical methods. The fiber orientation angles vary continuously around the shell circumference from 10 degrees on the shell crown and keel, to 45 degrees on the shell sides. The two shells differ in that one shell has the full 24-tow course applied during each pass of the fiber placement system, while the second shell uses the fiber placement system s tow drop/add capability to achieve a more uniform shell wall thickness. The shells are tested in axial compression, and estimates of their prebuckling axial stiffnesses and bifurcation buckling loads are predicted using linear finite element analyses. These preliminary predictions compare well with the test results, with an average agreement of approximately 10 percent.

/pdf/structural-assessment-of-advanced-composite-tow-steered-5an3kh04hu.pdf

Structural Assessment of Advanced Composite Tow-Steered Shells

Geometrically nonlinear truss structures with snap-through behavior are demonstrated by using an arc length approach within a finite element analysis. The instability patterns are equilibrium paths that are plotted throughout the snap-through event. Careful observation of these patterns helps to identify weak designs in large space structures, as well as identify desirable snap-through behavior in the miniaturization of electronic devices known as microelectromechanical systems (MEMS). Examples of highly nonlinear trusses that show snap-through behavior are examined by tracing their equilibrium paths.

/pdf/snap-through-instability-patterns-in-truss-structures-1ifpumvg7o.pdf

Snap-Through Instability Patterns in Truss Structures

https://ntrs.nasa.gov/api/citations/20090011260/downloads/20090011260.pdf

Optimization of stability-constrained geometrically nonlinear shallow trusses using an arc length sparse method with a strain energy density approach

A multi-center study was conducted in 2003 to assess the feasibility of and technology requirements for using aerocapture to insert a scientific platform into orbit around Neptune. The aerocapture technique offers a potential method of greatly reducing orbiter mass and thus total spacecraft launch mass by minimizing the required propulsion system mass. This study involved the collaborative efforts of personnel from Langley Research Center (LaRC), Johnson Space Flight Center (JSFC), Marshall Space Flight Center (MSFC), Ames Research Center (ARC), and the Jet Propulsion Laboratory (JPL). One aspect of this effort was the structural design of the full spacecraft configuration, including the ellipsled aerocapture orbiter and the in-space solar electric propulsion (SEP) module/cruise stage. This paper will discuss the functional and structural requirements for each of these components, some of the design trades leading to the final configuration, the loading environments, and the analysis methods used to ensure structural integrity. It will also highlight the design and structural challenges faced while trying to integrate all the mission requirements. Component sizes, materials, construction methods and analytical results, including masses and natural frequencies, will be presented, showing the feasibility of the resulting design for use in a Neptune aerocapture mission. Lastly, results of a post-study structural mass optimization effort on the ellipsled will be discussed, showing potential mass savings and their influence on structural strength and stiffness

/pdf/structural-design-for-a-neptune-aerocapture-mission-3l5j57sgn7.pdf

Structural Design for a Neptune Aerocapture Mission

Rigorous analysis of geometrically nonlinear structures demands creating mathematical models that accurately include loading and support conditions and, more importantly, model the stiffness and response of the structure. Nonlinear geometric structures often contain critical points with snap-through behavior during the response to large loads. Studying the post buckling behavior during a portion of a structure's unstable load history may be necessary. Primary structures made from ductile materials will stretch enough prior to failure for loads to redistribute producing sudden and often catastrophic collapses that are difficult to predict. The responses and redistribution of the internal loads during collapses and possible sharp snap-back of structures have frequently caused numerical difficulties in analysis procedures. The presence of critical stability points and unstable equilibrium paths are major difficulties that numerical solutions must pass to fully capture the nonlinear response. Some hurdles still exist in finding nonlinear responses of structures under large geometric changes. Predicting snap-through and snap-back of certain structures has been difficult and time consuming. Also difficult is finding how much load a structure may still carry safely. Highly geometrically nonlinear responses of structures exhibiting complex snap-back behavior are presented and analyzed with a finite element approach. The arc-length method will be reviewed and shown to predict the proper response and follow the nonlinear equilibrium path through limit points.

/pdf/geometrically-nonlinear-static-analysis-of-3d-trusses-using-4nu16towlp.pdf

Glenn A. Hrinda

Papers

Structural Assessment of Advanced Composite Tow-Steered Shells

Snap-Through Instability Patterns in Truss Structures

Optimization of stability-constrained geometrically nonlinear shallow trusses using an arc length sparse method with a strain energy density approach

Structural Design for a Neptune Aerocapture Mission

Geometrically Nonlinear Static Analysis of 3D Trusses Using the Arc-Length Method