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  • 1
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    Fracture of thick graphite/epoxy laminates with part-through surface flaws (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: Fracture behavior of tensile specimens containing through-the-thickness flaws and part-through semi-elliptic surface flaws was investigated. The material was T300/5208 graphite/epoxy, with a stacking sequence 0/+ or - 45/90 sub ns. Laminate thicknesses ranged from 8 to 120 plies. Fracture toughness for specimens with through-the-thickness flaws was a function of laminate thickness. Fracture toughness was also independent of crack size. Fracture toughness for the thick laminates was also independent of specimen geometry (center-cracked tension specimen, compact tension specimen, and three-point bend specimen). Using the asymptotic value of facture toughness and linear elastic isotropic fracture mechanics, the notched strength of tensile specimens with semi-elliptic surface flaws was predicted. The strength ratio is a function of the flaw depth (a/t) and flaw aspect (a/c) ratios. Comparisons between predicted and experimental strengths are good for large values of a/t. The notched strength of filament wound graphite/epoxy tensile specimens with part-through surface flaws was also predicted.
    Keywords: COMPOSITE MATERIALS
    Type: Proceedings of the 2nd Annual Review of the Center for Composite Materials and Structures; 11 p
    Format: text
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  • 2
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    A comparison of predicted and measured strengths of thick notched graphite/epoxy laminates (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The effect of thickness on the notched strength of three graphite/epoxy laminates is studied. The strength of the laminates is shown to be a function of laminate thickness. The notched strength of (0/+ or - 45/90)ns and (0/90)ns laminates decreased toward asymptotic values with increasing laminate thickness, while that of the (0/+ or - 45)ns laminate increased toward an asymptotic value with increasing laminate thickness. For all three laminate types, the notched strength decreased with increasing notch size, regardless of thickness. The fracture of the thick laminates was essentially uniform and self-similar with the notch. The 'universal' value of the general toughness parameter developed by Poe (1981) successfully predicts the notched strength of the thick laminates.
    Keywords: COMPOSITE MATERIALS
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  • 3
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    Fracture of thick graphite/epoxy laminates with part-through surface flaws (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Fracture behavior of tensile specimens containing through-the-thickness flaws and part-through semi-elliptic surface flaws was investigated. The material was T300/5208 graphite/epoxy, with a stacking sequence 0/+ or - 45/90 sub ns. Laminate thicknesses ranged from 8 to 120 plies. Fracture toughness for specimens with through-the-thickness flaws was a function of laminate thickness. Fracture toughness was also independent of crack size. Fracture toughness for the thick laminates was also independent of specimen geometry (center-cracked tension specimen, compact tension specimen, and three-point bend specimen). Using the asymptotic value of fracture toughness and linear elastic isotropic fracture mechanics, the notched strength of tensile specimens with semi-elliptic surface flaws was predicted. The strength ratio is a function of the flaw depth (a/t) and flaw aspect (a/c) ratios. Comparisons between predicted and experimental strengths are good for large values of a/t. The notched strength of filament wound graphite/epoxy tensile specimens with part-through surface flaws was also predicted.
    Keywords: COMPOSITE MATERIALS
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  • 4
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    Application of axisymmetric analog for calculating heating in three-dimensional flows (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 296-302
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  • 5
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    Computed and experimental surface pressure and heating on 70-deg sphere cones (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 385-393
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  • 6
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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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  • 7
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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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  • 8
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    Fracture and fatigue of discontinuously reinforced copper/tungsten composites (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: The strength, toughness and resistance to cyclic crack propagation of composites consisting of copper reinforced with short tungsten wires of various lengths have been studied and the results compared with the behavior of continuously reinforced composites manufactured by the same method, i.e., by vacuum hot-pressing. It has been found that whereas the resistance to fatigue crack growth of continuously reinforced composites is very similar to that of continuous Al/stainless steel composites reported elsewhere, the addition of short fibers completely changes the mode of fracture, and no direct comparisons are possible. In effect, short fibers inhibit single crack growth by causing plastic flow to be distributed rather than localized, and although these composites are much less strong than continuous fiber composites, they nevertheless have much greater fatigue resistance.
    Keywords: COMPOSITE MATERIALS
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  • 9
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    Internal state variable approach for predicting stiffness reductions in fibrous laminated composites with matrix cracks (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A mathematical model utilizing the internal state variable concept is proposed for predicting the upper bound of the reduced axial stiffnesses in cross-ply laminates with matrix cracks. The axial crack opening displacement is explicitly expressed in terms of the observable axial strain and the undamaged material properties. A crack parameter representing the effect of matrix cracks on the observable axial Young's modulus is calculated for glass/epoxy and graphite/epoxy material systems. The results show that the matrix crack opening displacement and the effective Young's modulus depend not on the crack length, but on its ratio to the crack spacing.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of Composite Materials (ISSN 0021-9983); 23; 1273-129
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  • 10
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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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