Effect of temperature on nonlinear tensile stress-strain behavior of CF/epoxy composites

This paper presents the effect of temperature on the nonlinear tensile stress-strain behavior of carbon fiber reinforced epoxy composites (CF/Epoxy). A two-dimensional elastic-plastic constitutive equation is developed using both a fourth-order complimentary energy function and a second-order one-parameter plastic potential, assuming that linear elastic deformation occurs in the fiber direction and anisotropy parameters change with plastic deformation. Monotonic and loading/unloading tensile tests on the on-axis and off-axis specimens at various temperatures are carried out to determine the elastic constants and plastic parameters of the effective stress-effective plastic strain relation. It is proved that nonlinearity in the transverse direction and the transverse-shear coupling is due to plastic deformation, while nonlinearity in the shear direction is ascribed not only to plasticity but also to nonlinear elasticity. The elastic constants in the transverse and shear directions and the plastic parameters are significantly affected by temperature. The off-axis tensile stress-strain curves predicted by using the present model show better agreement with the experimental results than those predicted by using Sun and Chen's model.