E-Glass/DGEBA/m-PDA Single Fiber Composites: The Effect of the Matrix Modulus on Interfacial Shear Strength Measurements

Published

June 1, 2000

Author(s)

Gale A. Holmes, Walter G. McDonough, R C. Peterson, Donald L. Hunston

Abstract

In this paper the nonlinear viscoelastic response of the diglycidyl ether of bisphenol-A (DGEBA)/meta-phenylenediamine (m-PDA) matrix was correlated with changes in the final fragment distribution. The changes in the final fragment distribution were induced by changes in the strain rate of the testing procedure (testing protocol). Since fiber fragmentation has been shown to occur when the matrix is exhibiting nonlinear viscoelastic behavior, the tangent modulus and the secant modulus in the nonlinear viscoelastic region were used to represent the matrix stiffness. In the nonlinear viscoelastic region, the tangent modulus was found to be influenced by the relaxation time between strain increments and hence, is very sensitive to the testing protocol. For three of the four specimens tested by the intermediate testing protocol the tangent modulus reached a plateau value of 1.1 GPa. In contrast, the tangent moduli of fiberless test specimens continued to decrease with increasing strain. By increasing the time between strain increments to 1 h (slow test protocol) the anomolous tangent modulus behavior found when the specimens were tested by the intermediate testing protocol was eliminated. The secant modulus did not vary dramatically under the same testing conditions. Therefore, the secant modulus was found to be preferable as an initial estimator of the matrix stiffness in the nonlinear viscoelastic (n-LVE) Cox model developed previously. When the stress-strain behavior of all the test specimens were examined, changes in the interfacial shear strength (IFSS) induced by changes in the testing protocol did not correlate with the bulk matrix stiffness. The observed changes in IFSS were explained in terms of the viscoelastic relaxation behavior of the matrix material in the fiber-matrix interface region.

Citation

Polymer Composites

Volume

21

Issue

3

Pub Type

Journals

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Keywords

epoxy, interfacial shear strength, micromechanics, modulus, single fiber composites, viscoelasticity, yielding

Citation

Holmes, G. , McDonough, W. , Peterson, R. and Hunston, D. (2000), E-Glass/DGEBA/m-PDA Single Fiber Composites: The Effect of the Matrix Modulus on Interfacial Shear Strength Measurements, Polymer Composites, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852075 (Accessed February 16, 2025)