STRESS-STRAIN RELATIONS OF A VISCOELASTIC COMPOSITE REINFORCED WITH ELLIPTIC CYLINDERS

The stress-strain behaviors of a two-phase composite comprising a visc oelastic matrix and elastic elliptic cylinders are examined by means o f a micromechanical theory. The reinforcing cylinders are taken to be aligned along direction 1 but randomly oriented in the 2-3 plane, with a common aspect ratio alpha (the thickness-to-width ratio). The strai n-rate sensitivity of the stress-strain curves of the transversely iso tropic composite is investigated as a function of the cross-sectional aspect ratio of the elliptic cylinders, and it is found that when the aspect ratio is one-corresponding to the traditional aligned fibers-th e reinforcement is the poorest and that when the aspect ratio approach es zero-corresponding to long, thin ribbons-it is the most effective. Other types of cross-sectional aspect ratios all give rise to a stress -strain curve lying between these two. Except for the thin ribbon with alpha --> 0 and axial tension for all, other types of reinforcement a ll exhibit a saturation stress under a constant strain rate and result in strong strain-rate sensitivity for the overall response of the sys tem.