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  • Other Sources  (4)
  • 1985-1989  (4)
  • 1975-1979
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  • 1
    facet.materialart.
    Unknown
    Optically controlled reflection modulator using GaAs-AlGaAs n-i-p-i/multiple-quantum-well structures (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: An optically controlled reflection modulator has been demonstrated that consists of a combination of a GaAs-AlGaAs n-i-p-i doping structure with a multiple-quantum-well structures on top of a distributed Bragg reflector, all grown by MBE. A modulation of approximately 60 percent is obtained on the test structure, corresponding to a differential change of absorption coefficient in the quantum wells of approximately 7500/cm. Changes in reflectance can be observed with a control beam power as low as 1.5 microW. This device structure has the potential of being developed as an optically addressed spatial light modulator for optical information processing.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Optics Letters (ISSN 0146-9592); 14; 230-232
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
    facet.materialart.
    Unknown
    Composite laminate free edge reinforcement concepts (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The presence of a free edge in a laminated composite structure can result in delamination of the composite under certain loading conditions. Linear finite element analysis predicts large or even singular interlaminar stresses near the free edge. Edge reinforcements which will reduce these interlaminar stresses, prevent or delay the onset of delaminations, and thereby increase the strength and life of the structure were studied. Finite element models are used to analyze reinforced laminates which were subsequently fabricated and loaded to failure in order to verify the analysis results.
    Keywords: COMPOSITE MATERIALS
    Type: Proceedings of the 2nd Annual Review of the Center for Composite Materials and Structures; 27 p
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
    facet.materialart.
    Unknown
    Reinforcement of composite laminate free edges with U-shaped caps (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Generalized plane strain finite element analysis is used to predict reduction of interlaminar normal stresses when a U-shaped cap is bonded to the edge of a laminate. Three-dimensional composite material failure criteria are used in a progressive laminate failure analysis to predict failure loads of laminates with different edge cap designs. In an experimental program, symmetric 11-layer graphite-epoxy laminates with a one-layer cap of Kevlar-epoxy cloth are shown to be 130 to 140 percent stronger than uncapped laminates under static tensile and tension-tension fatigue loading. In addition, the coefficient of variation of the static tensile failure load decreases from 24 to 8 percent when edge caps are added. The predicted failure load calculated with the finite element results is 10 percent lower than the actual failure load. For both capped and uncapped laminates, actual failure loads are much lower than those predicted using classical lamination theory stresses and a two-dimensional failure criterion. Possible applications of the free edge reinforcement concept are described, and future research is suggested.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 86-0972
    Format: text
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  • 4
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    Unknown
    Composite laminate free-edge reinforcement with U-shaped caps. I - Stress analysis. II - Theoretical-experimental correlation (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The present generalized plane-strain FEM analysis for the prediction of interlaminar normal stress reduction when a U-shaped cap is bonded to the edge of a composite laminate gives attention to the highly variable transverse stresses near the free edge, cap length and thickness, and a gap under the cap due to the manufacturing process. The load-transfer mechanism between cap and laminate is found to be strain-compatibility, rather than shear lag. In the second part of this work, the three-dimensional composite material failure criteria are used in a progressive laminate failure analysis to predict failure loads of laminates with different edge-cap designs; symmetric 11-layer graphite-epoxy laminates with a one-layer cap of kevlar-epoxy are shown to carry 130-140 percent greater loading than uncapped laminates, under static tensile and tension-tension fatigue loading.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 27; 610-623
    Format: text
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