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  • 1
    Publication Date: 2013-08-31
    Description: Composite structures have the potential to be cost-effective, structurally efficient primary aircraft structures. The Advanced Composites Technology (ACT) Program has the goal to develop the technology to exploit this potential for heavily loaded aircraft structures. As part of the ACT Program, Lockheed Aeronautical Systems Company completed the design and fabrication of the Technology Integration Box Beam (TIBB). The TIBB is an advanced composite prototype structure for the center wing section of the C-130 aircraft. Lockheed subjected the TIBB to downbending, upbending, torsion and combined upbending and torsion load conditions to verify the design. The TIBB failed at 83 percent of design ultimate load for the combined upbending and torsion load condition. The objective of this paper is to describe the mechanisms that led to the failure of the TIBB. The results of a comprehensive analytical and experimental study are presented. Analytical results include strain and deflection results from both a global analysis of the TIBB and a local analysis of the failure region. These analytical results are validated by experimental results from the TIBB tests. The analytical and experimental results from the TIBB tests are used to determine a sequence of events that resulted in failure of the TIBB. A potential cause of failure is high stresses in a stiffener runout region. Analytical and experimental results are also presented for a stiffener runout specimen that was used to simulate the TIBB failure mechanisms.
    Keywords: STRUCTURAL MECHANICS
    Type: Third NASA Advanced Composites Technology Conference, Volume 1, Part 2; p 951-965
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  • 2
    Publication Date: 2013-08-31
    Description: The objective of this paper is to describe current results from an on-going study of the mechanisms that led to the failure of the TIBB. Experimental and analytical results are presented. Experimental results include load, strain, and deflection data for the TIBB (Technology Integration Box Beam). An analytical investigation was conducted to compliment the experimental investigation and to gain additional insight into the TIBB structural response. Analytical results include strain and deflection results from a global analysis of the TIBB. A local analysis of the failure region is being completed. These analytical results are validated through comparisons with the experimental results from the TIBB tests. The experimental and analytical results from the TIBB tests are used to determine a sequence of events that may have resulted in failure of the TIBB. A potential cause of failure is high stresses in a stiffener runout region. Typical analytical results are presented for a stiffener runout specimen that is being defined to simulate the TIBB failure mechanisms. The results of this study are anticipated to provide better understanding of potential failure mechanisms in composite aircraft structures, to lead to future design improvements, and to identify needed analytical tools for design and analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: FAA, Ninth DOD(NASA)FAA Conference on Fibrous Composites in Structural Design, Volume 2; p 673-68
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  • 3
    Publication Date: 2011-08-24
    Description: The role of equation solvers in modern structural analysis software is described. Direct and iterative equation solvers which exploit vectorization on modern high-performance computer systems are described and compared. The direct solvers are two Cholesky factorization methods. The first method utilizes a novel variable-band data storage format to achieve very high computation rates and the second method uses a sparse data storage format designed to reduce the number od operations. The iterative solvers are preconditioned conjugate gradient methods. Two different preconditioners are included; the first uses a diagonal matrix storage scheme to achieve high computation rates and the second requires a sparse data storage scheme and converges to the solution in fewer iterations that the first. The impact of using all of the equation solvers in a common structural analysis software system is demonstrated by solving several representative structural analysis problems.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 33; 855-868
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  • 4
    Publication Date: 2013-08-31
    Description: CASES (Controls, Astrophysics and Structures Experiment in Space) is a proposed space experiment to collect x-ray images of the galactic center and solar disk with unprecedented resolution. This requires precision pointing and suppression of vibrations in the long flexible structure that comprises the 32-m x-ray telescope optical bench. Two separate electro-optical sensor systems are provided for the ground test facility (GTF). The Boom Motion Tracker (BMT) measures eigenvector data for post-mission use in system identification. The Tip Displacement Sensor (TDS) measures boom tip position and is used as feedback for the closed-loop control system that stabilizes the boom. Both the BMT and the TDS have met acceptance specifications and were delivered to MSFC in February 1992. This paper describes the sensor concept, the sensor configuration as implemented in the GTF, and the results of characterization and performance testing.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Fifth NASA(DOD Controls-Structures Interaction Technology Conference, Part 1; p 263-275
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  • 5
    Publication Date: 2013-08-31
    Description: Objectives of the research are: (1) to develop design requirements for damped struts to stabilize control system in the high frequency cross-over and spill-over range; (2) to design, fabricate and test viscously damped strut and viscoelastically damped strut; (3) to verify accuracy of design and analysis methodology of damped struts; and (4) to design and build test apparatus, and develop data reduction algorithm to measure strut complex stiffness. In order to meet the stringent performance requirements of the SPICE experiment, the active control system is used to suppress the dynamic responses of the low order structural modes. However, the control system also inadvertently drives some of the higher order modes unstable in the cross-over and spill-over frequency range. Passive damping is a reliable and effective way to provide damping to stabilize the control system. It also improves the robustness of the control system. Damping is designed into the SPICE testbed as an integral part of the control-structure technology.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Fifth NASA(DOD Controls-Structures Interaction Technology Conference, Part 1; p 239-249
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  • 6
    Publication Date: 2013-08-31
    Description: The 1990 UNIX version of NASTRAN was ported to two new platforms that are not supported by COSMIC: the Sun SPARC workstation and the Apple Macintosh using the A/UX version of UNIX. The experiences of the authers in porting NASTRAN is summarized here. Suggestions for users who might attempt similar ports are given.
    Keywords: STRUCTURAL MECHANICS
    Type: Computer Software Management and Information Center, Nineteenth NASTRAN (R) Users' Colloquium; p 14-21
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  • 7
    Publication Date: 2011-08-24
    Description: State-of-the-art nonlinear finite element analysis techniques are evaluated by applying them to a realistic aircraft structural component. A wing panel from the V-22 tiltrotor aircraft is chosen because it is a typical modern aircraft structural component for which there is experimental data for comparison of results. From blueprints and drawings, a very detailed finite element model containing 2284 9-node Assumed Natural-Coordinate Strain elements was generated. A novel solution strategy which accounts for geometric nonlinearity through the use of corotating element reference frames and nonlinear strain-displacement relations is used to analyze this detailed model. Results from linear analyses using the same finite element model are presented in order to illustrate the advantages and costs of the nonlinear analysis as compared with the more traditional linear analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: In: AHS National Technical Specialists' Meeting on Rotorcraft Structures, Williamsburg, VA, Oct. 29-31, 1991, Proceedings (A93-27951 10-05); 15 p.
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  • 8
    Publication Date: 2018-12-01
    Description: New finite element analysis methods are examined by application to a complicated composite wing panel from the V-22 rotorcraft. A detailed FEM model with a relatively coarse mesh of 9-node elements was generated, and linear and nonlinear stress analyses, first-ply failure analyses, and buckling analyses were conducted. At low values of applied load, i.e., up to the design ultimate load of the panel, the linear stress analysis accurately predicted the strains and structural response characteristics of the panel.
    Keywords: STRUCTURAL MECHANICS
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  • 9
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    In:  Other Sources
    Publication Date: 2019-07-13
    Description: FEM is here used to ascertain the stability and aeroelastic response of thin, 2D panels subjected to Mach 0.8-2.5 flows. In the absence of shocks, it is found that the Euler equations used to represent the unsteady flowfield dynamics predict response behaviors resembling those obtained via potential flow methods. Where shocks do play a significant role in the overall motion of the panel, divergence and limit cycle flutter are observed. In the Mach 1.4-1.5 range, flutter involved the higher modes of the panel, tending toward possible chaotic motion.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 93-1476 , ; 15 p.|AIAA, ASME, ASCE, AHS, and ASC, Structures, Structural Dynamics and Materials Conference, 34th and AIAA and ASME, Adaptive Structures Forum; Apr 19, 1993 - Apr 22, 1993; La Jolla, CA; United States
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  • 10
    Publication Date: 2019-07-13
    Description: The feasibility of changing the bolt shape from circular to elliptical in order to increase the joint strength was investigated. An analytical method using a cosine series to represent the bearing stress was derived, and a boundary collocation method was used to determine the unknown coefficients of this cosine series. Stresses at the hole edge predicted by the analytical method agreed very well with finite element solutions. Failure analyses of joints in two different laminates were performed, and each laminate exhibited a different joint failure mode. Results demonstrate that the joint strength of both laminates can be improved substantially by changing the bolt shape to elliptical. The joint that failed in a bearing mode showed a greater strength increase compared to the joint that failed in a shearing mode.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Reinforced Plastics and Composites (ISSN 0731-6844); 12; 2; p. 128-138.
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