Effects of fiber distribution on elastic–viscoplastic behavior of long fiber-reinforced laminates

In this paper, effects of transverse fiber distribution on the elastic–viscoplastic behavior of long fiber-reinforced laminates subjected to in-plane tensile loading are studied using a homogenization theory. To this end, a unit cell with random fiber distribution is arranged point-symmetrically with respect to cell facet centers and also Y-periodically. By discussing these two fiber arrangements in terms of standard deviations and a radial distribution function, it is demonstrated that the point-symmetric cell arrangement can enhance the randomness of fiber distribution in comparison with the Y-periodic arrangement. Then, on the assumption that the random fiber distribution generated by the point-symmetric cell arrangement prevails on the transverse section in each lamina, the in-plane elastic–viscoplastic deformation of carbon fiber/epoxy laminates is analyzed using a homogenization theory of nonlinear time-dependent composites. The analysis based on the perfectly periodic hexagonal fiber distribution in laminae is additionally performed for comparison. It is thus shown that the transverse randomness of fiber distribution in laminae has negligible influence on the macroscopic elastic–viscoplastic behavior of laminates, though it markedly affects the microscopic distribution of stress and strain. It is also shown that the analysis predicts very well the macroscopic behavior observed in the corresponding experiments.