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  • COMPOSITE MATERIALS  (12)
  • AIRCRAFT DESIGN, TESTING AND PERFORMANCE  (2)
  • 1
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    A fractographic investigation of the influence of stacking sequence on the strength of notched laminated composites (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The fracture behavior of T300/5208 CFRP laminate panels with 12 different combinations of ply orientation and stacking sequence is investigated experimentally, using optical microscopy, SEM, and X-ray radiography to characterize the notch-tip damage zones and fracture surfaces of center-cracked tension specimens subjected to tensile loading at constant crosshead displacement rate 20 micron/s. The results are presented graphically and analyzed in detail. Significant differences in notched strength are found for different ply fiber orientations and stacking sequences; the laminates with few major delaminations had a greater percentage of fracture due to broken fibers and also higher notched strength.
    Keywords: COMPOSITE MATERIALS
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  • 2
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    An experimental investigation of the fracture behavior of thick, notched laminated composites (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The fracture of high-modulus fiber-reinforced graphite/epoxy laminates with machined crack-like notches is discussed. An experimental program was conducted, in which stacking sequence,laminate thickness, notch size, and specimen configuration have been investigated. This research has led to the fundamental observation that heterogeneity significantly effects the fracture of thin laminates but has a relatively insignificant effect on the fracture of thick laminates. The results of this program are reviewed with the emphasis on the notch sensitivity and design of thick laminates.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of the Mechanical Behavior of Materials (ISSN 0334-8938); 1; 1-4,; 55-79
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  • 3
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    Progressive failure methodologies for predicting residual strength and life of laminated composites (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Two progressive failure methodologies currently under development by the Mechanics of Materials Branch at NASA Langley Research Center are discussed. The damage tolerance/fail safety methodology developed by O'Brien is an engineering approach to ensuring adequate durability and damage tolerance by treating only delamination onset and the subsequent delamination accumulation through the laminate thickness. The continuum damage model developed by Allen and Harris employs continuum damage laws to predict laminate strength and life. The philosophy, mechanics framework, and current implementation status of each methodology are presented.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 843-873
    Format: application/pdf
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  • 4
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    Recent progress in NASA Langley textile reinforced composites program (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The NASA LaRC is conducting and sponsoring research to explore the benefits of textile reinforced composites for civil transport aircraft primary structures. The objective of this program is to develop and demonstrate the potential of affordable textile reinforced composite materials to meet design properties and damage tolerance requirements of advanced aircraft structural concepts. In addition to in-house research, the program was recently expanded to include major participation by the aircraft industry and aerospace textile companies. The major program elements include development of textile preforms, processing science, mechanics of materials, experimental characterization of materials, and development and evaluation of textile reinforced composite structural elements and subcomponents. The NASA Langley in-house focus is as follows: development of a science-based understanding of resin transfer molding (RTM), development of powder-coated towpreg processes, analysis methodology, and development of a performance database on textile reinforced composites. The focus of the textile industry participation is on development of multidirectional, damage-tolerant preforms, and the aircraft industry participation is in the areas of design, fabrication and testing of textile reinforced composite structural elements and subcomponents. Textile processes such as 3D weaving, 2D and 3D braiding, and knitting/stitching are being compared with conventional laminated tape processes for improved damage tolerance. Through-the-thickness reinforcements offer significant damage tolerance improvements. However, these gains must be weighed against potential loss in in-plane properties such as strength and stiffness. Analytical trade studies are underway to establish design guidelines for the application of textile material forms to meet specific loading requirements. Fabrication and testing of large structural components are required to establish the full potential of textile reinforced composite materials.
    Keywords: COMPOSITE MATERIALS
    Type: FAA, Ninth DOD(NASA)FAA Conference on Fibrous Composites in Structural Design, Volume 2; p 845-87
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  • 5
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    Recent progress in NASA Langley Research Center textile reinforced composites program (1992)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: Research was conducted to explore the benefits of textile reinforced composites for transport aircraft primary structures. The objective is to develop and demonstrate the potential of affordable textile reinforced composite materials to meet design properties and damage tolerance requirements of advanced aircraft structural concepts. Some program elements include development of textile preforms, processing science, mechanics of materials, experimental characterization of materials, and development and evaluation of textile reinforced composite structural elements and subcomponents. Textile 3-D weaving, 3-D braiding, and knitting and/or stitching are being compared with conventional laminated tape processes for improved damage tolerance. Through-the-thickness reinforcements offer significant damage tolerance improvements. However, these gains must be weighted against potential loss in in-plane properties such as strength and stiffness. Analytical trade studies are underway to establish design guidelines for the application of textile material forms to meet specific loading requirements. Fabrication and testing of large structural parts are required to establish the potential of textile reinforced composite materials.
    Keywords: COMPOSITE MATERIALS
    Type: Second NASA Advanced Composites Technology Conference; p 295-323
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  • 6
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    Analytical and experimental investigation of the notched strength of thick laminates with surface notches (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Experimental and analytical investigations of the fracture of a graphite/epoxy laminate with part-through semielliptic surface notches have been conducted. Experimental values of notched strength were determined for a variety of notch aspect ratios and notch depths. Analytical predictions of laminate failure were obtained from three different models. The three models were equally successful in predicting the fracture of laminates with deep notches. The experimental results of laminates with shallow notches indicated more notch sensitivity (that is greater strength reduction) than did the analytical models.
    Keywords: COMPOSITE MATERIALS
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  • 7
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    Mechanics of Textile Composites Conference (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This document is a compilation of papers presented at the Mechanics of Textile Composites Conference in Hampton, Virginia, December 6-8, 1994. This conference was the culmination of a 3-year program that was initiated by NASA late in 1990 to develop mechanics of textile composites in support of the NASA Advance Composites Technology Program (ACT). The goal of the program was to develop mathematical models of textile preform materials and test methods to facilitate structural analysis and design. Participants in the program were from NASA, academia, and industry.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-CP-3311-PT-2 , NAS 1.55:3311-PT-2 , L-17532B , NIPS-96-06187
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  • 8
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    A procedure for utilization of a damage-dependent constitutive model for laminated composites (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Described here is the procedure for utilizing a damage constitutive model to predict progressive damage growth in laminated composites. In this model, the effects of the internal damage are represented by strain-like second order tensorial damage variables and enter the analysis through damage dependent ply level and laminate level constitutive equations. The growth of matrix cracks due to fatigue loading is predicted by an experimentally based damage evolutionary relationship. This model is incorporated into a computer code called FLAMSTR. This code is capable of predicting the constitutive response and matrix crack damage accumulation in fatigue loaded laminated composites. The structure and usage of FLAMSTR are presented along with sample input and output files to assist the code user. As an example problem, an analysis of crossply laminates subjected to two stage fatigue loading was conducted and the resulting damage accumulation and stress redistribution were examined to determine the effect of variations in fatigue load amplitude applied during the first stage of the load history. It was found that the model predicts a significant loading history effect on damage evolution.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-104219 , NAS 1.15:104219
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  • 9
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    Recent fracture mechanics results from NASA research related to the aging commercial transport fleet (1991)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: NASA is conducting the Airframe Structural Integrity Program in support of the aging commercial transport fleet. This interdisciplinary program is being worked in cooperation with the U.S. airframe manufacturers, airline operators, and the FAA. Advanced analysis methods are under development to predict the fatigue crack growth in complex built-up shell structures. Innovative nondestructive examination technologies are also under development to provide large area inspection capability to detect corrosion, disbonds, and fatigue cracks. Recent fracture mechanics results applicable to predicting the growth of cracks initiating at the rivets of fuselage splice joints are reviewed.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AGARD, Fatigue Management; 6 p
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  • 10
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    A micromechanics model of the stiffness and strength of laminates with fiber waviness (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A mathematical model based on the Euler-Bernoulli beam theory is proposed for predicting the effective Young's moduli of piecewise isotropic composite laminates with local ply curvatures in the main load-carrying layers. Strains in corrugated layers, In-Phase layers, Out-of-Phase layers are predicted for various geometries and material configurations by assuming matrix layers as elastic foundations of different spring constants. The effective Young's moduli measured from corrugated aluminum specimens and aluminum/epoxy specimens with In-Phase and Out-of-Phase wavy patterns coincide very well with the model predictions. Moire fringe analysis of an In-Phase specimen and an Out-of-Phase specimen are also presented confirming the main assumption of the model related to the elastic constraint due to the matrix layers. The present model is also compared with the experimental results and other models, including the micro-buckling models, published in the literature. The results of the present study show that even a very small scale local ply curvature produces a noticeable effect on the mechanical constitutive behavior of a laminated composite.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-CR-181670 , NAS 1.26:181670
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