Abstract
Although it has been experimentally shown that the addition of short-fibers slows the stress relaxation process in composites, the underlying phenomenon is complex and not well understood. Previous studies have proposed that fibers slow the relaxation process by either hindering the movement of nearby polymeric chains or by creating additional covalent bonds at the fiber-matrix interface that must be broken before bulk relaxation can occur. In this study, we propose a simplified analytical model that explicitly accounts for the influence of polymer viscoelasticity on shear stress transfer to the fibers. This model adequately explains the effect of fiber addition on the relaxation behavior without the need to postulate structural changes at the fiber-matrix interface. The model predictions were compared to those from Monte Carlo finite-element simulations, and good agreement between the two was observed.
Highlights
The interaction between the fiber and the matrix in a short-fiber composite is quite complex. the effect of fibers on static properties such as modulus and strength is well understood, it has been a challenge to understand the effect of fibers on the viscoelastic properties of short-fiber composites
The effect of fibers on static properties such as modulus and strength is well understood, it has been a challenge to understand the effect of fibers on the viscoelastic properties of short-fiber composites. These properties are extremely important in load bearing applications where there is the potential for creep or stress relaxation, or where the composites are exposed to any sort of dynamic loading, and it is important to be able to predict the influence of fiber reinforcement on the viscoelasticity
It has been experimentally shown that the presence of short-fibers slows the relaxation process in composites, the underlying phenomenon is complex and was not well understood
Summary
The interaction between the fiber and the matrix in a short-fiber composite is quite complex. Blackley and Pike proposed that the relaxation of composites was affected by the additional covalent bonds between the fibers and the matrix and that the rupture of these bonds during stress relaxation caused an accelerated response, changing the relaxation time constant [3] In this and other early investigations, both the reinforcing fibers and the matrix were viscoelastic materials, and these early studies showed that the addition of short-fibers increased the relaxation rate, almost all the more recent studies have shown the opposite effect [4,5]. These studies propose that breaking the additional covalent bonds at the fiber-matrix interface is a prerequisite to polymer mobility and relaxation To test this idea, a number of researchers have examined the effect of various coupling agents and their effect on stress relaxation behavior. In the second part of this paper, we will compare the predictions from the analytical model to the results obtained from the Monte Carlo finite-element simulations
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