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Research Papers

Effects of Manufacturing-Induced Voids on Local Failure in Polymer-Based Composites

[+] Author and Article Information
K. A. Chowdhury, R. Talreja, A. A. Benzerga

Department of Aerospace Engineering, Texas A&M University, College Station, TX 77843

J. Eng. Mater. Technol 130(2), 021010 (Mar 13, 2008) (9 pages) doi:10.1115/1.2841529 History: Received August 03, 2007; Revised January 08, 2008; Published March 13, 2008

This paper presents results of a computational study focused on examining the role of manufacturing-induced voids in the initiation and growth of damage at the microstructural level in polymer matrix composites loaded in tension normal to fibers. The polymer deformation is described by an improved macromolecular constitutive model accounting for strain-rate-, pressure-, and temperature-sensitive yielding, isotropic hardening before peak yield, intrinsic postyield softening, and rapid anisotropic hardening at large strains. A new craze model that accounts for craze initiation, growth, and breakdown mechanisms is employed. An energy-based criterion is used for cavitation induced cracking that can lead to fiber/matrix debonding. The role of voids is clarified by conducting a comparative study of unit cells with and without voids. The effects of strain rate and temperature are investigated by a parametric study. The overall composite stress-strain response is also depicted to indicate manifestation of microlevel failure on macroscopic behavior.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Typical damage initiation mechanisms in a carbon/epoxy composite. Matrix crack initiated (a) from fiber debonding and (b) from void resulting in fiber debonding. After Ref. 10.

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Figure 2

Geometry of the idealized unit cell of a composite microstructure with a manufacturing-induced void

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Figure 3

Finite element mesh used for (a) the sound cell (2014 quadrilateral elements) and (b) the void cell (4047 elements)

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Figure 4

True stress versus true strain curves for plane strain compression of a PMMA material using the original (22) and modified (this paper) macromolecular models, compared with experimental data of Ref. 45 at T=25°C and ε̇=0.001s−1

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Figure 5

Calculated stress-strain responses of PMMA for (a) plane strain tension at T=90°C and different strain rates; (b) plane strain compression at ε̇=0.001s−1 and different temperatures

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Figure 6

Overall stress versus strain responses of the sound and void unit cells of the PMMA composite at T=25°C and a nominal strain rate Ė=1s−1

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Figure 7

Contours of the maximum principal stress σI and development of fracture in the (a) sound and (b) voided unit cells of the PMMA composite at T=25°C and a nominal strain rate Ė=1s−1

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Figure 8

Overall stress versus strain responses of the void unit cell of the PMMA composite at Ė=1s−1 and varying temperature

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Figure 9

Contours of the maximum principal stress σI and development of fracture in the void unit cell of the PMMA composite at Ė=1s−1 and two temperatures: (a) T=0°C and (b) T=110°C

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Figure 10

Variation of effective properties with temperature at nominal strain rate Ė=1s−1. (a) Strain to failure Ei versus T. (b) Maximum axial stress supported by the unit cell versus T.

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Figure 11

Overall stress versus strain responses of the void unit cell of the PMMA composite at T=90°C and varying strain rate

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Figure 12

Contours of the maximum principal stress σI and development of fracture in the void unit cell of the PMMA composite at T=90°C and two strain rates: (a) Ė=10−3s−1 and (b) Ė=1s−1

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Figure 13

Variation of effective properties with strain rate at T=90°C. (a) Strain to failure Ei versus nominal strain rate Ė. (b) Maximum axial stress supported by the unit cell versus Ė.

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