Effect of Deformation-Induced Change of Fiber Orientation on Nonlinear Behavior of Polymeric Composite Laminates

Abstract

Abstract Deformation can cause some change in fiber orientation in composite laminates. The purpose of this paper was to investigate the effect of such fiber orientation on the nonlinear behavior of polymeric composite laminates. Overstress viscoplasticity model was used to describe the rate-dependent nonlinear behavior of the composite lamina, and the laminate was modeled with the classical laminated plate theory. To verify the model, experiments were conducted on various laminate specimens of IM7/5260 and AS4/PEEK composites at different loading rates. The thermal residual stresses induced during curing were included using a simple thermoelasticity method. It was found that when curing stresses were not taken into consideration, the laminated plate theory would predict stiffer nonlinear responses than the data from the experimental results. For such laminates, the predictions with curing stresses are softer than without thermal stress, and usually good agreement between predictions and experiments can be reached. However, for some other laminates such as [±30°]ns, the predictions without curing stresses are too soft compared with the experimental data at relatively high strain level, and the consideration of curing stresses may make the predictions even worse. Moreover, such deviation between predictions and experiments cannot be remedied by considering possible damage or delamination in the laminates, since these factors will reduce the stiffness of the material. As a result, the theory will predict an even softer response if these factors are taken into account. It is clear that some other factors might be responsible for the deviation. In this study, we found that the change of fiber orientation induced by deformation could play an important role in nonlinear stress-strain behavior. For angle ply laminates with θ greater than 45°, curing stresses are dominant in the behavior, and the change of fiber orientation has no effect. For θ lying between 20° and 40°, the curing stresses have a significant effect at low strain levels, while fiber orientation change has a greater effect at high strain levels.