Quantitative modelling of viscoelasticity of isotropic fibrous composites with viscoelastic matrices

Despite the wide usage of isotropic fibrous composites with a viscoelastic polymer matrix, no analytic model for their mechanical behaviour is known. This paper develops such a model for time-dependent Young's modulus, showing that for typical constituents the time constants of composites are up to about 6% greater than the matrix shear time constant. Viscoelasticity is strongly suppressed for stiff fibres even at modest fibre volume fractions. Comparison with known results for particle and oriented fibre composites confirms isotropic fibrous composites as between the two in terms of viscoelastic behaviour, but more similar to the latter.