On the importance of strain rate dependence in high velocity impacts of woven CFRP fragments: Experimental and numerical methodology

This work presents a novel combined experimental-numerical methodology to analyse the behaviour of carbon/epoxy woven fragments, when impacting a rigid target at high velocity (up to 160 m/s). On the one hand, the experimental methodology developed is capable of measuring the impact force using a Hopkinson bar device; the images obtained by means of ultra-high speed cameras are used to analyse the different failure modes during the fracture process, providing abetter understanding of the physical phenomena. On the other hand, a numerical methodology is developed to highlight the importance of considering the strain rate dependence in the constitutive model and to demonstrate the significant influence it has on the behaviour of CFRP fragments during the impact. Using this combined approach, it is possible to unveil the different roles of the damage mechanisms that appear in the CFRP fragment, and how they influence the impact force and impulse exerted; the inclusion of the strain rate dependence in the material model not only provides an increase in strength but also controls the failure mode. Finally, thanks to the numerical approach, a parametric study of fragment misalignment is carried out to present its influence on the failure mechanisms and in the results of force and impulse. The conclusions drawn represent a significant improvement in the understanding of the behaviour of composite materials acting as projectiles.