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  • 1
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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
    Details
    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
    Format: text
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  • 2
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    Fracture mechanics research at NASA related to the aging commercial transport fleet (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    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 and an extensive testing program is under way to study fatigue crack growth and fracture in complex built-up shell structures. Innovative nondestructive examination technologies are also being developed to provide large area inspection capability to detect corrosion, disbonds, and cracks. Recent fracture mechanics results applicable to predicting the growth of cracks under monotonic and cyclic loading at rivets in fuselage lap-splice joints are reviewed.
    Keywords: STRUCTURAL MECHANICS
    Type: The 1991 International Conference on Aging Aircraft and Structural Airworthiness; p 75-91
    Format: text
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  • 3
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    Development of advanced structural analysis methodologies for predicting widespread fatigue damage in aircraft structures (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: NASA is developing a 'tool box' that includes a number of advanced structural analysis computer codes which, taken together, represent the comprehensive fracture mechanics capability required to predict the onset of widespread fatigue damage. These structural analysis tools have complementary and specialized capabilities ranging from a finite-element-based stress-analysis code for two- and three-dimensional built-up structures with cracks to a fatigue and fracture analysis code that uses stress-intensity factors and material-property data found in 'look-up' tables or from equations. NASA is conducting critical experiments necessary to verify the predictive capabilities of the codes, and these tests represent a first step in the technology-validation and industry-acceptance processes. NASA has established cooperative programs with aircraft manufacturers to facilitate the comprehensive transfer of this technology by making these advanced structural analysis codes available to industry.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-110187 , NAS 1.15:110187
    Format: application/pdf
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  • 4
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    A review of nonlinear constitutive models for metals (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Over the past two decades a number of thermomechanical constitutive theories have been proposed for viscoplastic metals. These models are in most cases similar in that they utilize a set of internal state variables which provide locally averaged representations of microphysical phenomena such as dislocation rearrangement and grain boundary sliding. The state of development of several of these models is now at the point where accurate theoretical solutions can be obtained for a wide variety of structural problems at elevated temperatures. The fundamentals of viscoplasticity are briefly reviewed and a general framework is outlined. Several of the more prominent models are reviewed, and predictions from models are compared to experimental results.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-102727 , NAS 1.15:102727
    Format: application/pdf
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  • 5
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    A cumulative damage model for continuous fiber composite laminates with matrix cracking and interply delaminations (1988)
    In:  Other Sources
    Details
    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
    Format: text
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  • 6
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    A model for predicting damage induced fatigue life of laminated composite structural components (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: This paper presents a model for predicting the life of laminated composite structural components subjected to fatigue induced microstructural damage. The model uses the concept of continuum damage mechanics, wherein the effects of microcracks are incorporated into a damage dependent lamination theory instead of treating each crack as an internal boundary. Internal variables are formulated to account for the effects of both matrix cracks and internal delaminations. Evolution laws for determining the damage variables as functions of ply stresses are proposed, and comparisons of predicted damage evolution are made to experiment. In addition, predicted stiffness losses, as well as ply stresses are shown as functions of damage state for a variety of stacking sequences.
    Keywords: STRUCTURAL MECHANICS
    Type: ICAS Congress; Sept. 9-14, 1990; Stockholm; Sweden
    Format: text
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  • 7
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    An evaluation of the pressure proof test concept for thin sheet 2024-T3 (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The concept of pressure proof testing of fuselage structures with fatigue cracks to insure structural integrity was evaluated from a fracture mechanics viewpoint. A generic analytical and experimental investigation was conducted on uniaxially loaded flat panels with crack configurations and stress levels typical of longitudinal lap splice joints in commercial transport aircraft fuselages. The results revealed that the remaining fatigue life after a proof test was longer than that without the proof test because of crack growth retardation due to increased crack closure. However, based on a crack length that is slightly less than the critical value at the maximum proof test stress, the minimum assured life or proof test interval must be no more than 550 pressure cycles for a 1.33 proof factor and 1530 pressure cycles for a 1.5 proof factor to prevent in-flight failures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-101675 , NAS 1.15:101675
    Format: application/pdf
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  • 8
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    NASA airframe structural integrity program (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: NASA initiated a research program with the long-term objective of supporting the aerospace industry in addressing issues related to the aging of the commercial transport fleet. The program combines advanced fatigue crack growth prediction methodology with innovative nondestructive examination technology with the focus on multi-stage damage (MSD) at rivited connections. A fracture mechanics evaluation of the concept of pressure proof testing the fuselage to screen for MSD was completed. A successful laboratory demonstration of the ability of the thermal flux method to detect disbonds at rivited lap splice joints was conducted. All long-term program elements were initiated, and the plans for the methodology verification program are being coordinated with the airframe manufacturers.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-102637 , NAS 1.15:102637
    Format: application/pdf
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  • 9
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    Computational Methods for Failure Analysis and Life Prediction (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This conference publication contains the presentations and discussions from the joint UVA/NASA Workshop on Computational Methods for Failure Analysis and Life Prediction held at NASA Langley Research Center 14-15 Oct. 1992. The presentations focused on damage failure and life predictions of polymer-matrix composite structures. They covered some of the research activities at NASA Langley, NASA Lewis, Southwest Research Institute, industry, and universities. Both airframes and propulsion systems were considered.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CP-3230 , L-17321 , NAS 1.55:3230 , Oct 14, 1992 - Oct 15, 1992; Hampton, VA; United States
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  • 10
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    Predictions of Poisson's ratio in cross-ply laminates containing matrix cracks and delaminations (1989)
    In:  Other Sources
    Details
    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
    Format: text
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