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  • COMPOSITE MATERIALS  (19)
  • Life Sciences (General)  (1)
  • Spacecraft Design, Testing and Performance  (1)
  • 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
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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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    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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  • 5
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    Assessment of the State-of-the-Art in the Design and Manufacturing of Large Composite Structure (2001)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: This viewgraph presentation gives an assessment of the state-of-the-art in the design and manufacturing of large component structures, including details on the use of continuous fiber reinforced polymer matrix composites (CFRP) in commercial and military aircraft and in space launch vehicles. Project risk mitigation plans must include a building-block test approach to structural design development, manufacturing process scale-up development tests, and pre-flight ground tests to verify structural integrity. The potential benefits of composite structures justifies NASA's investment in developing the technology. Advanced composite structures technology is enabling to virtually every Aero-Space Technology Enterprise Goal.
    Keywords: Life Sciences (General)
    Type: Proceedings of The 4th Conference on Aerospace Materials, Processes, and Environmental Technology; NASA/CP-2001-210427
    Format: application/pdf
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  • 6
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    Fracture of thick laminated composites (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The fracture of thick laminated graphite/epoxy composites has been the subject of an extensive research program. The program was divided into three major areas of investigation which included laminate thickness, laminate stacking sequence, and part-through surface flaws. The results from this program are reviewed with emphasis placed on their applicability to the design of thick laminated composite structures.
    Keywords: COMPOSITE MATERIALS
    Type: Experimental Mechanics (ISSN 0014-4851); 26; 34-41
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  • 7
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    Tension fracture of laminates for transport fuselage. Part 1: Material screening (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Transport fuselage structures are designed to contain pressure following a large penetrating damage event. Application of composites to fuselage structures requires a data base and supporting analysis on tension damage tolerance. Tests with 430 fracture specimens were used to accomplish the following: (1) identify critical material and laminate variables affecting notch sensitivity, (2) evaluate composite failure criteria, and (3) recommend a screening test method. Variables studied included fiber type, matrix toughness, lamination manufacturing process, and intraply hybridization. The laminates found to have the lowest notch sensitivity were manufactured using automated tow placement. This suggests a possible relationship between the stress distribution and repeatable levels of material inhomogeneity that are larger than found in traditional tape laminates. Laminates with the highest notch sensitivity consisted of toughened matrix materials that were resistant to a splitting phenomena that reduces stress concentrations in load bearing plies. Parameters for conventional fracture criteria were found to increase with the crack length of the smallest notch sizes studied. Most materials and laminate combinations followed less than a square root singularity for the largest crack sizes studied. Specimen geometry, notch type, and notch size were evaluated in developing a screening test procedure. Results indicate that a range of notch sizes must be tested to determine notch sensitivity.
    Keywords: COMPOSITE MATERIALS
    Type: Second NASA Advanced Composites Technology Conference; p 197-238
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  • 8
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    Effect of laminate thickness and specimen configuration on the fracture of laminated composites (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Attention is given to the effect of laminate thickness on graphite/epoxy laminates in the present measurements of fracture toughness in center cracked tension specimens, compact tension specimens, and three-point bend specimens. Crack tip damage development prior to fracture is also studied. The results obtained show fracture toughness to be a function of laminate thickness, being in all cases independent of crack size. The fracture surface of all thick laminates was uniform in the interior and self-similar with the starter notch. With only one exception, the fracture toughness of the thicker laminates was relatively independent of specimen configuration.
    Keywords: COMPOSITE MATERIALS
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  • 9
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    Role of delamination and damage development on the strength of thick notched laminates (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A large, comprehensive program is being conducted at Virginia Tech to study the effect of laminate thickness on the fracture strength of notched laminated composites. Part of this program has been the study of the chracteristics and development of subcritical crack-tip damage prior to failure. The study has concentrated on the center-cracked tension specimen geometry. Subcritical crack-tip damage has been studied using enhanced X-ray radiography and the laminate deply technique. This paper examines he role that delamination plays in affecting the fracture of (0/+ or - 45/90)ns and (0/+ or - 45)ns laminates at various values of n. The study has found that delaminations do occur in thin laminates (n = 1) and affect the strength of the laminate. However, in thick laminates such as (0/+ or 45)90ns, and (0/+ or - 45)20s, there is sufficient constraint to prevent delaminations from occurring in the interior region of he specimen. The final fracture surface is uniform in the interior and self-similar (collinear with the original starter notch), with 'shear-lip' type damage in the form of delaminations and matrix cracking in the first several plies at the surface. These differences in the type of fracture of the thin and thick laminates greatly affect the fracture strength.
    Keywords: COMPOSITE MATERIALS
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  • 10
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    A damage tolerant design parameter for graphite/epoxy laminated composites (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The results of an extensive experimental investigation of the fracture behavior of notched graphite/epoxy laminates are presented. Twenty-seven laminates with different stacking sequences and laminate thicknesses have been studied. The data presented herein suggest that a damage tolerant design parameter exists that is relatively independent of ply stacking sequence and laminate thickness.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of Composites Technology and Research; 7; 77-81
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