Energy absorption model and damage behavior of GrNPs reinforced GFRP laminate composites under ballistic impact

The incorporation of an appropriate weight ratio of nano-fillers into glass fiber reinforced resin-based composites (GFRP) can effectively improve their impact resistance and energy absorption characteristics. In this study, nano-graphite particles (GrNPs) were used as a matrix filler, and a systematic investigation was conducted on the effects of varying graphite content (0wt.%, 5 wt.%, 10 wt.% and 15 wt.%) and impact velocity (200∼800 m/s) on the energy absorption and damage characteristics of laminates. An impact energy absorption model was established by considering delamination failure and multiple energy absorption mechanisms. The contributions of various forms of energy, including tensile failure of the primary fibers, deformation of the secondary fibers, shear plugging, delamination, matrix cracking and cone kinetic energy, to the impact energy dissipation were determined at different impact velocities. A mesoscopic finite element model of GrNPs reinforced GFRP (GrNPs-GFRP) laminates was developed based on the virtual fiber method, and the dynamic impact response of GrNPs-GFRP laminates was analyzed using Micro-CT and scanning electron microscopy (SEM). The results indicate that under the impact condition of 200 m/s, the total energy absorption from shear plugging, primary fibers, and secondary fibers exceed 90 %. Compared to pure GFRP laminates, the energy absorption due to shear plugging in GrNPs (5 wt.%) reinforced GFRP laminates increase from 56.1 % to 63.9 %, while the energy absorption from secondary fibers decreases from 21.4 % to 17.1 %, and the energy absorption from primary fibers decreased from 20.4 % to 17.6 %. Under the impact condition of 400 m/s, the energy absorption due to shear plugging in the laminates increase, while the energy absorption in the secondary fiber region decrease due to the reduced contact time between the projectile and target. As the impact velocity increase to approximately 600 m/s, energy absorption in the primary fiber region continues to rise, and the energy absorption of the shear plugging reaches the upper limit. The energy absorption due to delamination and matrix failure has been significantly increased with the rise in impact velocity. When the impact velocity was increase from 400 m/s to 700 m/s, the energy absorption ratio due to delamination increase from 0.9 % to 6.9 %, while the energy absorption ratio due to matrix cracking rises from 1.9 % to 15.5 %. The excellent impact resistance exhibits by GrNPs (5 wt.%) is attributed to the dispersion hardening effect, which improves interlaminar toughness and facilitates the dissipation of impact energy.