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  • 1
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    Moment distributions around holes in symmetric composite laminates subjected to bending moments (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 28; 877-882
    Format: text
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  • 2
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    Investigating compression failure mechanisms in composite laminates with a transient fiberglass-epoxy birefringent material (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: An experimental study is reported in which a nondestructive technique involving the use of a transparent fiberglass-epoxy composite birefringent material has been used to investigate compression failure mechanisms in graphite-epoxy laminates. It is shown that the birefringency and transparency of the fiberglass-epoxy material permits regions of high stress to be located and the mechanisms of local failure propagation to be identified within the laminate. The material may also be useful for studying stress fields and for identifying failure initiation and propagation mechanisms in a wide variety of composite-structure problems.
    Keywords: COMPOSITE MATERIALS
    Type: Experimental Techniques (ISSN 0732-8818); 8; 24
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  • 3
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    Experimental behavior of graphite-epoxy Y-stiffened specimens loaded in compression (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An experimental investigation of the behavior of graphite-epoxy Y-stiffened specimens loaded in compression is presented. Experimental results are presented for element specimens with a single stiffener and for panel specimens with three stiffeners. Response and failure characteristics of the specimens are described. Effects of impact damage on structural response for both specimen configurations are also presented. Results indicate that impact location may significantly affect the residual strength of the Y-stiffened specimens. The failure results indicate that the critical failure mode is buckling of the stiffener webs for Y-stiffened element specimens and buckling of both stiffener web and stiffener blade for the Y-stiffened panel specimens.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 953-968
    Format: application/pdf
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  • 4
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    Effects of cutouts on the behavior of symmetric composite laminates subjected to bending and twisting loads (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Composite structures are used for a wide variety of aerospace applications. Practical structures contain cutouts and these structures are subjected to in-plane and out-of-plane loading conditions. Structurally efficient designs for composite structures require a thorough understanding of the effects of cutouts on the response of composite plates subjected to inplane or out-of-plane loadings. Most investigations of the behavior of composite plates with cutouts have considered in-plane loadings only. Out-of-plane loadings suchas bending or twisting have received very limited attention. The response of homogeneous plates (e.g., isotropic or orthotropic plates) subjected to bending or twisting moments has been studied analytically. These analyses are for infinite plates and neglect finite-plate effects. Recently, analytical and experimental studies were conducted to determine the effects of cutouts on the response of laminated composite plates subjected to bending moments. No analytical or experimental results are currently available for the effects of cutouts on the response of composite laminates subjected to twisting moments.
    Keywords: COMPOSITE MATERIALS
    Type: Third NASA Advanced Composites Technology Conference, Volume 1, Part 2; p 899-918
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  • 5
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    Technology integration box beam failure study (1993)
    In:  CASI
    Details
    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
    Format: application/pdf
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  • 6
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    A Protection And Detection Surface (PADS) for damage tolerance (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: A protection and detection surface (PADS) concept was studied for application to composite primary aircraft structures. A Kevlar-epoxy woven face sheet with a Rohacell foam core was found to be the most effective PADS configuration among the configurations evaluated. The weight of the PADS configuration was estimated to be approximately 17 percent of the structural weight. The PADS configuration was bonded to graphite-epoxy base laminates, and up to a 70 percent improvement in compression-after-impact failure strains was observed.
    Keywords: COMPOSITE MATERIALS
    Type: Eighth DOD(NASA)FAA Conference on Fibrous Composites in Structural Design, Part 1; p 199-219
    Format: text
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  • 7
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    Sandwich beam compressive test method (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Tests presented show that the sandwich beam in four-point bending could be used to obtain reliable compressive elastic constants for graphite/polyimide laminates although some difficulties were encountered measuring composite compressive strengths. Data were obtained for ultimate stress, ultimate strain, Young's modulus, and Poisson's ratio values in 117K, room temperature, and 589K test environments for the HTS1/PMR-15 material system. A total of 36 compressive tests on various laminates were performed. Also, 24 tensile tests on the same laminate orientations were performed to obtain input to the analytical portion of this program. A portion of the beam test section was analyzed using a linear elastic finite element computer program to predict the stress state in the graphite/polyimide composite. The influence of the honeycomb core of this stress state was analytically determined.
    Keywords: COMPOSITE MATERIALS
    Type: Graphite/Polyimide Composites; p 189-200
    Format: text
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  • 8
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    Compression behavior of + or - 45 deg-dominated laminates with a circular hole or impact damage (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 24; 115-122
    Format: text
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  • 9
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    Short-wavelength buckling and shear failures for compression-loaded composite laminates (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The short-wavelength buckling (or the microbuckling) and the interlaminar and inplane shear failures of multi-directional composite laminates loaded in uniaxial compression are investigated. A laminate model is presented that idealizes each lamina. The fibers in the lamina are modeled as a plate, and the matrix in the lamina is modeled as an elastic foundation. The out-of-plane w displacement for each plate is expressed as a trigonometric series in the half-wavelength of the mode shape for laminate short-wavelength buckling. Nonlinear strain-displacement relations are used. The model is applied to symmetric laminates having linear material behavior. The laminates are loaded in uniform end shortening and are simply supported. A linear analysis is used to determine the laminate stress, strain, and mode shape when short-wavelength buckling occurs. The equations for the laminate compressive stress at short-wavelength buckling are dominated by matrix contributions.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-87640 , NAS 1.15:87640
    Format: application/pdf
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  • 10
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    Compression failure of angle-ply laminates (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Test results from the compression loading of (+ or - Theta/ - or + Theta)(sub 6s) angle-ply IM7-8551-7a specimens, 0 less than or = Theta less than or = 90 degs, are presented. The observed failure strengths and modes are discussed, and typical stress-strain relations shown. Using classical lamination theory and the maximum stress criterion, an attempt is made to predict failure stress as a function of Theta. This attempt results in poor correlation with test results and thus a more advanced model is used. The model, which is based on a geometrically nonlinear theory, and which was taken from previous work, includes the influence of observed layer waviness. The waviness is described by the wave length and the wave amplitude. The theory is briefly described and results from the theory are correlated with test results. It is shown that by using levels of waviness observed in the specimens, the correlation between predictions and observations is good.
    Keywords: COMPOSITE MATERIALS
    Type: FAA, Ninth DOD(NASA)FAA Conference on Fibrous Composites in Structural Design, Volume 1; p 185-19
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