Nonlinear Viscoelastic Behavior of the Fiber-Matrix Interphase: Theory and Experiment

Abstract

In fiber-matrix bonding, which is the topic of this paper, a common method of measuring the quality of adhesion is the single fiber fragmentation test procedure [1]. Various elastic and elastic-plastic approaches have been used in the literature to study the micro-mechanics of stress transfer between fiber and matrix. The most commonly used relation assumes uniform fiber strength and expresses the adhesion strength, τ_c, in the form

$$ {\tau_c} = \left( {{\sigma_f}\;d} \right)/\left( {2\;{l_c}} \right) $$

(1)

where, τ_c is the shear strength at the fiber resin interface, d is the fiber diameter, l _c is the critical fiber fragment size and, σ_f is the fiber tensile strength. For the present work single fiber tension test specimens were prepared by embedding single carbon fibers (7µm Celion G30 500 sized and unsized) in Epon 815 epoxy (Shell) cured with DETA and Armocure 100 (Akzo Chemie America) into 2 X 3 X 140 mm dog-bone tensile coupons with 50 mm gage length.