Impact characterization of a carbon fiber-epoxy laminate using a nonconservative model

The study of polymer and composite behavior under high strain rates is of fundamental relevance to determine the material suitability for a selected application. However, the impact phenomenon is a very complicated event, mainly due to the short duration, large deformation, and high stresses developed in the sample. In this work, we have performed impact tests over a carbon fiber reinforced epoxy using low-energy in the striker. A nonconservative and nonlineal spring-dashpot series model has been proposed to reproduce the material behavior. The model considers simultaneously both flexural and indentation phenomena accounting for energy losses by means of the restitution coefficient. Using this model, an excellent fit between the predicted and the experimental force-time trace has been obtained below the composite failure point, which was recognized by a separation of both mentioned curves. As the epoxy-fiber laminate has a very low viscoelasticity, the high strain rate Youngʹs modulus obtained from the model was compared with that extracted from a conventional three point bending test, finding a very good match between the values. The study of the dashpot coefficients allows concluding that the dominant mechanism is the composite flexion, while the indentation effects contribution takes on importance at low impact velocities.