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RESEARCH PAPERS

A Mechanistic Approach to Matrix Cracking Coupled with Fiber–Matrix Debonding in Short-Fiber Composites

[+] Author and Article Information
Ba Nghiep Nguyen1

 Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352

Brian J. Tucker, Mohammad A. Khaleel

 Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352

1

Corresponding author. Telephone: (509) 375-3634; Fax: (509) 375-6736. E-mail address: ba.nguyen@pnl.gov

J. Eng. Mater. Technol 127(3), 337-350 (Mar 22, 2005) (14 pages) doi:10.1115/1.1924565 History: Received October 11, 2004; Revised March 22, 2005

A micro–macro mechanistic approach to damage in short-fiber composites is developed in this paper. At the microscale, a reference aligned fiber composite is considered for the analysis of the damage mechanisms such as matrix cracking and fiber–matrix debonding using the modified Mori–Tanaka model. The associated damage variables are defined, and the stiffness reduction law dependent on these variables is established. The stiffness of a random fiber composite containing random matrix microcracks and imperfect interfaces is then obtained from that of the reference composite, which is averaged over all possible orientations and weighted by an orientation distribution function. The macroscopic response is determined using a continuum damage mechanics approach and finite element analysis. Final failure resulting from saturation of matrix microcracks, fiber pull-out and breakage is modeled by a vanishing element technique. The model is validated using the experimental results found in literature as well as the results obtained for a random chopped fiber glass–vinyl ester system. Acoustic emission techniques were used to quantify the amount and type of damage during quasi-static testing.

Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the multiscale modeling approach to short-fiber composites

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Figure 2

Schematic of the evolutions of the damage variables

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Figure 3

Cumulative amplitude distribution during a tensile test for a random glass–vinyl ester specimen

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Figure 4

Distribution of AE events along the (glass–vinyl ester) specimen length between two sensors

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Figure 5

Participation rates of the damage mechanisms vs the applied stress

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Figure 6

Evolution of the damage variable β* as a function of the crack density α

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Figure 7

Quasi-static test setup

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Figure 8

Data acquisition setup

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Figure 9

Stiffness reduction due to matrix cracking computed for the random 1200tex glass–epoxy composite

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Figure 10

Stiffness reduction due to matrix cracking and fiber–matrix debonding computed for the random glass–vinyl ester material

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Figure 11

Tensile stress–strain responses for the random 1200tex glass–epoxy samples: The values denoted by the symbols were extracted from the experimental curves given in (7).

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Figure 12

Applied stress vs crack density for the random 1200tex glass–epoxy system: The experimental values denoted by the symbols are from Ref. 7.

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Figure 13

Predicted and experimental tensile stress–strain responses for the random glass–vinyl ester specimens

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Figure 14

Applied stress vs crack density for the random glass–vinyl ester specimens

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Figure 15

Finite element mesh used for the damage analysis of the random glass–vinyl ester plate containing two holes and under tensile loading

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Figure 16

Distribution of the matrix microcrack density (damage variable α) in the plate at the onset of failure (for the applied stress of 60MPa)

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Figure 17

Damage accumulation by fiber–matrix debonding (damage variable β*) in the plate at the onset of failure (for the applied stress of 60MPa)

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Figure 18

Contour of the longitudinal stress (MPa) σ11 in the plate at the onset of failure for the applied stress of 60MPa

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Figure 19

Distribution of the matrix microcrack density in the plate for the applied stress of 90MPa: After initiation, macroscopic cracks first propagate perpendicular to the loading direction. After that the crack patterns tend to deviate from the initial propagation direction.

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Figure 20

Damage accumulation by fiber–matrix debonding (damage variable β*) in the plate for the applied stress of 90MPa

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Figure 21

Experimental (a)–(c) and predicted (d) damage and failure progressions in the plate for the applied stress about 113MPa (final failure stress).

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