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  • 1
    Electronic Resource
    Electronic Resource
    An accurate shear-deformable six-node triangular plate element for laminated composite structures (1994)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 431-455 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A six-node triangle plate/shell element is developed for the analysis of laminated composite structures. This model is formulated using Hamilton's principle along with a first-order (Reissner/Mindlin) shear deformation theory. The element is based upon an isoparametric representation along with an interdependent interpolation strategy; bicubic polynomials for the transverse displacement and biquadratic polynomials for the element geometry, in-plane displacements and rotations. The resulting element, which is evaluated using exact numerical integration, has correct rank and is free of shear ‘locking’. Numerical results are presented that validate the new element and prove its outstanding convergence capabilities in comparison to existing triangular elements using standardized test problems (elastic eigenvalue analysis, patch test, static simply supported square-plate solutions) and experimentally measured vibration data of cantilevered isotropic and composite plates.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620370305
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    An accurate two-node finite element for shear deformable curved beams (1998)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 41 (1998), S. 473-498 
    Details
    ISSN: 0029-5981
    Keywords: shear deformable ; curved beams ; two node finite element ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An accurate two-node (three degrees of freedom per node) finite element is developed for curved shear deformable beams. The element formulation is based on shape functions that satisfy the homogeneous form of the partial differential equations of motion which renders it free of shear and membrane locking. The element is demonstrated to converge to the results obtained from a shear deformable straight beam when the beam becomes shallower. Numerical examples were performed to demonstrate the accuracy and efficiency with respect to previously published formulations. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 3
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    Damage detection in elastic structures using vibratory residual forces and weighted sensitivity (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A methodology is presented for detecting structural damage in elastic structures by nondestructive means. Measured modal test data along with a correlated analytical structural model are used to locate potentially damaged regions using residual modal force vectors and to conduct a weighted sensitivity analysis to assess the extent of mass and/or stiffness variations, where damage is characterized as a stiffness reduction. The current approach is unique among other approaches in that it accounts for (1) variations in system mass, system stiffness, and mass center (locations), (2) perturbations of both the natural frequencies and modal vectors, and (3) statistical confidence factors for the structural parameters and potential experimental instrumentation error. Moreover, this procedure can be used with either full or reduced models. A wide variety of numerical examples are presented that show that the current method provides a precise indication of both the location and the extent of structural damage.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 30; 9, Se; 2310-231
    Format: text
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  • 4
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    A new beam theory using first-order warping functions (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Due to a certain type of loading and geometrical boundary conditions, each beam will respond differently depending on its geometrical form of the cross section and its material definition. As an example, consider an isotropic rectangular beam under pure bending. Plane sections perpendicular to the longitudinal axis of the beam will remain plane and perpendicular to the deformed axis after deformation. However, due to the Poisson effect, particles in the planes will move relative to each other resulting in a form of anticlastic deformation. In other words, even in pure bending of an isotropic beam, each cross section will deform in the plane. If the material of the beam above is replaced by a generally anisotropic material, then the cross sections will not only deform in the plane, but also out of plane. Hence, in general, both in-plane deformation and out-of-plane warping will exist and depend on the geometrical form and material definition of the cross sections and also on the loadings. For the purpose of explanation, an analogy is made. The geometrical forms of the bodies of each individual are unique. Hence, different sizes of clothes are needed. Finding the sizes of clothes for individuals is like determining the warping functions in beams. A new beam theory using first-order warping functions is introduced. Numerical examples will be presented for an isotropic beam with rectangular cross section. The theory can be extended for composite beams.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Langley Research Center, Research in Structures, Structural Dynamics and Materials, 1990; p 85-102
    Format: application/pdf
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  • 5
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    Extension-torsion coupling behavior of advanced composite tilt-rotor blades (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An analytic model was developed to study the extension-bend-twist coupling behavior of an advanced composite helicopter or tilt-rotor blade. The outer surface of the blade is defined by rotating an arbitrary cross section about an initial twist axis. The cross section can be nonhomogeneous and composed of generally anisotropic materials. The model is developed based upon a three dimensional elasticity approach that is recast as a coupled two-dimensional boundary value problem defined in a curvilinear coordinate system. Displacement solutions are written in terms of known functions that represent extension, bending, and twisting and unknown functions for local cross section deformations. The unknown local deformation functions are determined by applying the principle of minimum potential energy to the discretized two-dimensional cross section. This is an application of the Ritz method, where the trial function family is the displacement field associated with a finite element (8-node isoparametric quadrilaterals) representation of the section. A computer program was written where the cross section is discretized into 8-node quadrilateral subregions. Initially the program was verified using previously published results (both three-dimensional elasticity and technical beam theory) for pretwisted isotropic bars with an elliptical cross section. In addition, solid and thin-wall multi-cell NACA-0012 airfoil sections were analyzed to illustrate the pronounced effects that pretwist, initial twist axis location, and spar location has on coupled behavior. Currently, a series of advanced composite airfoils are being modeled in order to assess how the use of laminated composite materials interacts with pretwist to alter the coupling behavior of the blade. These studies will investigate the use of different ply angle orientations and the use of symmetric versus unsymmetric laminates.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Old Dominion Univ., NASA/American Society for Engineering Ed; Old Dominion Univ.,
    Format: application/pdf
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  • 6
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    Using experimental modal data to detect damage in a space truss (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The effects of damage on a model space truss are investigated using experimentally measured modes along with a procedure that uses the vibratory residual forces and a weighted sensitivity analysis to estimate the extent of mass and/or stiffness variations, where damage is characterized as a reduction in structural stiffness. It is shown that this approach yields excellent results for a four-bay space truss under consideration and was able to accurately predict not only the location of the damage region but also estimate the relative severity for three different configurations. In addition, the method was able to accurately detect and differentiate a shift in structural mass.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 93-1486 , In: AIAA(ASME)ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 34th and AIAA/ASME Adaptive Structures Forum, La Jolla, CA, Apr. 19-22, 1993, Technical Papers. Pt. 3 (A93-33876 1; p. 1556-1564.
    Format: text
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  • 7
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    Behavior of spinning laminated composite plates with initial twist-experimental vibrations, strain, and deflection results (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The experimental behavior of spinning, pre-twisted laminated composite plates was investigated. The purpose of these experiments was to establish an experimental database consisting of strain, deflections, and natural frequencies as a function of rotational velocity. Six different plate sets were tested, that included three different stacking sequences (two symmetric, one asymmetric), two different initial twist levels (0 deg, 30 deg), and two different initial twist axis locations (midchord, quarter-chord). The plates were spin tested at four different combinations of pitch and sweep. It was observed that the location of the pretwist axis and the level of pretwist greatly affects the strain and deflections of the spinning plate, while only the pretwist level affects the measured natural frequencies.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 93-1325 , In: AIAA(ASME)ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 34th and AIAA/ASME Adaptive Structures Forum, La Jolla, CA, Apr. 19-22, 1993, Technical Papers. Pt. 1 (A93-33876 1; p. 255-265.
    Format: text
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  • 8
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    The development of a generalized advanced propeller analysis system (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A Generalized Advanced Propeller Analysis System (GAPAS) is being developed to provide both an optimized design and a performance evaluation capability. The technology areas incorporated in GAPAS include propeller aerodynamic performance, airfoil loading, acoustics, structural analysis and aeroelasticity. The propeller analyses include the most advanced, fully-developed technologies in a modular but unified system. The program will treat multi-bladed propellers having straight or swept blades operating on aircraft at speeds to Mach 0.8 and altitudes to 40,000 feet. The purpose of this paper is twofold. First, it will introduce the GAPAS program to the general industry; and second, since the GAPAS program will be made available for general applications, it is also intended to be a status report on the development stage of the program.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: AIAA PAPER 83-2466
    Format: text
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  • 9
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    Generalized Advanced Propeller Analysis System (GAPAS). Volume 2: Computer program user manual (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Generalized Advanced Propeller Analysis System (GAPAS) computer code is described. GAPAS was developed to analyze advanced technology multi-bladed propellers which operate on aircraft with speeds up to Mach 0.8 and altitudes up to 40,000 feet. GAPAS includes technology for analyzing aerodynamic, structural, and acoustic performance of propellers. The computer code was developed for the CDC 7600 computer and is currently available for industrial use on the NASA Langley computer. A description of all the analytical models incorporated in GAPAS is included. Sample calculations are also described as well as users requirements for modifying the analysis system. Computer system core requirements and running times are also discussed.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-185277 , NAS 1.26:185277
    Format: application/pdf
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  • 10
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    Extension-bend-twist coupling behavior of nonhomogeneous anisotropic beams with initial twist (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 30; 519-527
    Format: text
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