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A research program is being undertaken to develop rate dependent deformation and failure models for the analysis of polymer matrix composite materials. In previous work in this program, strain-rate dependent inelastic constitutive equations used to analyze polymers have been implemented into a mechanics of materials based composite micromechanics method. In the current work, modifications to the micromechanics model have been implemented to improve the calculation of the effective inelastic strain. Additionally, modifications to the polymer constitutive model are discussed in which pressure dependence is incorporated into the equations in order to improve the calculation of constituent and composite shear stresses. The Hashin failure criterion is implemented into the analysis method to allow for the calculation of ply level failure stresses. The deformation response and failure stresses for two representative uniaxial polymer matrix composites, IM7/977-2 and AS4-PEEK, are predicted for varying strain rates and fiber orientations. The predicted results compare favorably to experimentally obtained values.Goldberg, Robert K. and Stouffer, Donald C.Glenn Research CenterPOLYMER MATRIX COMPOSITES; DEFORMATION; STRAIN RATE; FAILURE ANALYSIS; MICROMECHANICS; PRESSURE DEPENDENCE; SHEAR STRESS; FIBER ORIENTATION; FAILURE; CONSTITUTIVE EQUATIONS; CRITERIA
Product Details :
Genre |
: |
Author |
: National Aeronautics and Space Administration (NASA) |
Publisher |
: Createspace Independent Publishing Platform |
Release |
: 2018-06-04 |
File |
: 34 Pages |
ISBN-13 |
: 1720669694 |
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BOOK EXCERPT:
Product Details :
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: |
Release |
: 1999 |
File |
: 38 Pages |
ISBN-13 |
: NASA:31769000631930 |
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Product Details :
Genre |
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Author |
: Robert Keith Goldberg |
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: |
Release |
: 1999 |
File |
: 88 Pages |
ISBN-13 |
: NASA:31769000634843 |
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Product Details :
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Author |
: Robert K. Goldberg |
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: |
Release |
: 2000 |
File |
: 28 Pages |
ISBN-13 |
: NASA:31769000639503 |
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BOOK EXCERPT:
Product Details :
Genre |
: |
Author |
: Robert K. Goldberg |
Publisher |
: |
Release |
: 1999 |
File |
: 154 Pages |
ISBN-13 |
: OCLC:858260811 |
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BOOK EXCERPT:
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Author |
: Robert K. Goldberg |
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: |
Release |
: 1999 |
File |
: 16 Pages |
ISBN-13 |
: NASA:31769000633589 |
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BOOK EXCERPT:
"With the increasing application of fiber reinforced polymer matrix composites in the aerospace industry, a composite model that has the capability to capture the nonlinear, strain rate dependent deformation behavior of the materials is desired for finite element analysis. Polymers are believed to be the major contributors to the nonlinearity and rate dependence of the composites. In this study, the nonlinear, rate dependent constitutive polymer model developed by Goldberg has been modified to incorporate the rate dependence of the elastic modulus and a simple damage model is proposed to improve its unloading prediction. The polymer constitutive equations are then implemented within a strength of materials based micromechanics method in order to predict the nonlinear, strain rate dependent deformation of the composite. Strain rate dependent failure criteria and post failure progressive damage model are incorporated into the composite model. The polymer and the composite models are implemented into a commercially available explicit finite element code, LS-DYNA, as user defined materials (UMATs). The deformation behaviors of several representative polymers and two polymer matrix composites of various fiber configurations are simulated in LS-DYNA with the UMATs for a wide range of strain rates, and the numerical results agree well with the experimental data. To expand the application of the unidirectional lamina based composite UMAT, braiding/weaving with through-thickness integration points method is proposed with examples to simulate the deformation behavior of textile composites."--Iii-iv.
Product Details :
Genre |
: Polymeric composites |
Author |
: Xiahua Zheng |
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: |
Release |
: 2006 |
File |
: 340 Pages |
ISBN-13 |
: OCLC:156939872 |
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Release |
: 1998 |
File |
: 42 Pages |
ISBN-13 |
: NASA:31769000628860 |
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BOOK EXCERPT:
The results presented here are part of an ongoing research program, to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. A micromechanics approach is employed in this work, in which state variable constitutive equations originally developed for metals have been modified to model the deformation of the polymer matrix, and a strength of materials based micromechanics method is used to predict the effective response of the composite. In the analysis of the inelastic deformation of the polymer matrix, the definitions of the effective stress and effective inelastic strain have been modified in order to account for the effect of hydrostatic stresses, which are significant in polymers. Two representative polymers, a toughened epoxy and a brittle epoxy, are characterized through the use of data from tensile and shear tests across a variety of strain rates. Results computed by using the developed constitutive equations correlate well with data generated via experiments. The procedure used to incorporate the constitutive equations within a micromechanics method is presented, and sample calculations of the deformation response of a composite for various fiber orientations and strain rates are discussed.Goldberg, Robert K. and Roberts, Gary D. and Gilat, AmosGlenn Research CenterCONSTITUTIVE EQUATIONS; DEFORMATION; IMPACT LOADS; MICROMECHANICS; POLYMER MATRIX COMPOSITES; STRAIN RATE; BRITTLENESS; EPOXY RESINS; FAILURE ANALYSIS; FIBER ORIENTATION; HYDROSTATICS; MATRIX MATERIALS; TENSILE TESTS; SHEAR PROPERTIES
Product Details :
Genre |
: |
Author |
: National Aeronautics and Space Administration (NASA) |
Publisher |
: Createspace Independent Publishing Platform |
Release |
: 2018-06 |
File |
: 34 Pages |
ISBN-13 |
: 1720579938 |
eBook Download
BOOK EXCERPT:
Product Details :
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: |
Author |
: |
Publisher |
: |
Release |
: 2002 |
File |
: 34 Pages |
ISBN-13 |
: NASA:31769000646730 |