Abstract
The addition of short fibers has been experimentally observed to slow the stress relaxation of viscoelastic polymers, producing a change in the relaxation time constant. Our recent study attributed this effect of fibers on stress relaxation behavior to the interfacial shear stress transfer at the fiber-matrix interface. This model explained the effect of fiber addition on stress relaxation without the need to postulate structural changes at the interface. In our previous study, we developed an analytical model for the effect of fully aligned short fibers, and the model predictions were successfully compared to finite element simulations. However, in most industrial applications of short-fiber composites, fibers are not aligned, and hence it is necessary to examine the time dependence of viscoelastic polymers containing randomly oriented short fibers. In this study, we propose an analytical model to predict the stress relaxation behavior of short-fiber composites where the fibers are randomly oriented. The model predictions were compared to results obtained from Monte Carlo finite element simulations, and good agreement between the two was observed. The analytical model provides an excellent tool to accurately predict the stress relaxation behavior of randomly oriented short-fiber composites.
Highlights
The high modulus of short-fiber-reinforced polymers has made them useful in demanding load-bearing applications such as high-performance sporting equipment
The accuracy of the model was determined by plotting the analytical model predictions against the finite element experimental results, and comparing the slope of this line to that of a y = x line
The goal of this study was to investigate the role of short fibers on stress relaxation behavior by examining micromechanics the fiber-matrix interface infibers composites with randomlybehavior orientedby
Summary
The high modulus of short-fiber-reinforced polymers has made them useful in demanding load-bearing applications such as high-performance sporting equipment. Because of the inherent viscoelasticity of the matrix phase, polymer composites are prone to creep [1] and stress relaxation, making it a challenge when considering composites for long-term applications. A better understanding of composite viscoelasticity is needed so that long-term behavior can be better predicted. Since viscoelastic properties all result from the same molecular mechanisms, a model for stress relaxation in composites would shed light on creep or dynamic mechanical behavior. The interaction between the fiber and matrix in a short-fiber composite is quite complex, and it has been a challenge to understand the effect of fibers on the viscoelastic properties of these materials
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