Abstract
In this work, the homogenized elastic-viscoplastic behavior of long fiber-reinforced laminates under in-plane loading is predicted by taking directly into account the micro-scopic structure and stacking sequence of laminae. To this end, a homogenization theory of nonlinear time-dependent composites is applied to such laminates, leading to the macro-scopic rate-type constitutive equation of laminates and the evolution equations of micro-scopic and average stresses in each lamina. The macroscopic constitutive equation has a stiffness tensor and a stress relaxation function which are evaluated explicitly in terms of the microscopic structure and stacking sequence of laminae. To verify the present theory, uniaxial tensile tests are performed on carbon fiber/epoxy laminates. It is thus shown that the present theory is successful in predicting the anisotropic viscoplasticity in in-plane tension of unidirectional and cross-ply laminates and the negligible viscoplasticity exhibited by quasi-isotropic laminates.
