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  • 1985-1989  (10)
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  • 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
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    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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    A micromechanics model for the effective Young's modulus of a piecewise-isotropic laminate with wavy patterns (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A mathematical model based on the Euler-Bernoulli beam theory is proposed for predicting the effective Young's moduli of piece-wise isotropic composite laminates with wavy patterns in the main load-carrying layers. Strains in corrugated layers, in-phase layers, and out-of-phase layers are predicted for various geometries and material configurations by assuming matrix layers as elastic foundations. Experimental results obtained from corrugated aluminum specimens and aluminum/epoxy specimens with in-phase and out-of-phase wavy patterns coincide very well with the predictions. The work represents a preliminary effort toward further generalization of the model for two-dimensional anisotropic laminates containing wavy patterns in the main load-carrying layers.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials (ISSN 0021-9983); 22; 717-741
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  • 4
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    Analytical and experimental investigation of the notched strength of thick laminates with surface notches (1988)
    In:  Other Sources
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    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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  • 5
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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
    Format: application/pdf
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  • 6
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    A cumulative damage model for continuous fiber composite laminates with matrix cracking and interply delaminations (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The present cumulative damage model for the prediction of stiffness loss in graphite/epoxy laminates applies a thermomechanical constitutive theory for elastic composites with distributed damage. The model proceeds from a continuum mechanics and thermodynamics approach in which the distributed damage is characterized by a set of second-order tensor-valued internal state variables. A set of damage-dependent laminated plate equations is obtained; this is developed by modifying classical Kirchhoff plate theory.
    Keywords: STRUCTURAL MECHANICS
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  • 7
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    Predictions of Poisson's ratio in cross-ply laminates containing matrix cracks and delaminations (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A damage-dependent constitutive model for laminated composites has been developed for the combined damage modes of matrix cracks and delaminations. The model is based on the concept of continuum damage mechanics and uses second-order tensor valued internal state variables to represent each mode of damage. The internal state variables are defined as the local volume average of the relative crack face displacements. Since the local volume for delaminations is specified at the laminate level, the constitutive model takes the form of laminate analysis equations modified by the internal state variables. Model implementation is demonstrated for the laminate engineering modulus E(x) and Poisson's ratio nu(xy) of quasi-isotropic and cross-ply laminates. The model predictions are in close agreement to experimental results obtained for graphite/epoxy laminates.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composites Technology and Research (ISSN 0885-6804); 11; 53-58
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  • 8
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    A mechanics framework for a progressive failure methodology for laminated composites (1989)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A laminate strength and life prediction methodology has been postulated for laminated composites which accounts for the progressive development of microstructural damage to structural failure. A damage dependent constitutive model predicts the stress redistribution in an average sense that accompanies damage development in laminates. Each mode of microstructural damage is represented by a second-order tensor valued internal state variable which is a strain like quantity. The mechanics framework together with the global-local strategy for predicting laminate strength and life is presented in the paper. The kinematic effects of damage are represented by effective engineering moduli in the global analysis and the results of the global analysis provide the boundary conditions for the local ply level stress analysis. Damage evolution laws are based on experimental results.
    Keywords: STRUCTURAL MECHANICS
    Type: American Society for Composites, Technical Conference; Oct 03, 1989 - Oct 06, 1989; Blacksburg, VA; United States|; 16 p.
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  • 9
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    A continuum damage model of fatigue-induced damage in laminated composites (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A model is presented which predicts the stress-strain behavior of continuous fiber reinforced laminated composites in the presence of microstructural damage. The model is based on the concept of continuum damage mechanics and uses internal state variables to characterize the various damage modes. The associated internal state variable growth laws are mathematical models of the loading history induced development of microstructural damage. The model is demonstrated by using it to predict the response of damaged AS-4/3502 graphite/epoxy laminate panels.
    Keywords: COMPOSITE MATERIALS
    Type: SAMPE Journal (ISSN 0091-1062); 24; 43-51
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  • 10
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    Predicting the strength of filament-wound specimens with surface cuts (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The notched strength of filament-wound composite specimens was determined for coupons with various sized semielliptic surface notches. When the part-through notches did not cut the first 0-deg layer the strength was independent of the size of the notch and was equal to the unnotched tensile strength. When the cut penetrated 0-deg layers, the specimens failed in a two-part failure mode. The first part of the failure was modeled using fracture mechanics and a straight line tangent to the fracture mechanics solution, and the second part of the failure was modeled using a failure criterion that accounted for the moduli of 0-deg and helical layers.
    Keywords: STRUCTURAL MECHANICS
    Type: International SAMPE Symposium and Exhibition; May 08, 1989 - May 11, 1989; Reno, NV; United States
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