Simple constitutive model for nonlinear response of fiber-reinforced composites with loading-directional dependence

Polymeric composites generally exhibit different nonlinear response in tension and compression tests. In this study, Sun and Chen’s one-parameter plasticity model [Sun C.T. and Chen J.L., 1989. A simple flow rule for characterizing nonlinear behavior of fiber composites, J Compos Mater 29, 457–463] is extended to incorporate the loading-directional dependence on the plastic flow in composite laminates. Off-axis specimens of unidirectional carbon/epoxy composites were tested in compression and tension. Based on experimental results of compression tests, a simple two-parameter constitutive model for characterizing nonlinear mechanical behavior of fiber-reinforced composites was established. Finally, comparison of model predictions with experimental results of off-axis tension tests indicated a good correlation between the two. The developed simple plasticity model can explain the difference of nonlinear response in tension and compression tests.