Negative through-the-thickness Poisson’s ratio of elastic–viscoplastic angle-ply carbon fiber-reinforced plastic laminates: Homogenization analysis

Negative through-the-thickness Poisson’s ratios are investigated macroscopically and microscopically in the elastic–viscoplastic behavior of angle-ply carbon fiber-reinforced plastic (CFRP) laminates. For this purpose, an analysis method is proposed based on a homogenization theory for nonlinear time-dependent composites with point-symmetric internal structures. This method is able to efficiently analyze both the macroscopic and microscopic elastic–viscoplastic properties of angle-ply CFRP laminates fully modeled with microstructures consisting of fibers and a matrix. Using the proposed method, the elastic–viscoplastic analysis of angle-ply carbon fiber/epoxy laminates with various laminate configurations is performed to investigate their Poisson’s ratios in the viscoplastic region. It is revealed that, for a range of laminate configurations, the through-the-thickness Poisson’s ratios exhibit negative values which become increasingly negative as the viscoplastic deformation progresses in the laminates. The effect of strain rate on this increasing negativity is also demonstrated, and microscopic mechanisms are investigated to explain this trend. It is further shown that the increasing negativity significantly affects microscopic interlaminar stress distributions.