Damage mechanisms in composite laminated shells subjected to multiple impacts at different points

This study investigates the effect of damage interference resulting from impact loads on the mechanical response and impact fatigue life of E-glass/epoxy composite laminate shells. The analysis involves single impacts at different points to evaluate the impact strength's dependency on boundary conditions. Notably, there is a gradual reduction in both maximum impact force and absorbed energy beyond 10 mm from the centre, towards unconstrained edges, accompanied by an increase in displacement. Specifically, at a distance of 30 mm, the maximum force and absorbed energy register a decrease of 9.4% and 7.9%, respectively, while the displacement rises by 14.5%. The findings reveal that the damage severity decreases as the impact point is closer to the unconstrained edge of the specimen, which can be attributed to a stiffness reduction, which can reach up to 22%. Symmetrically induced pre-damages exhibit no discernible effect on the subsequent impact response. It is observed that beyond 10 mm from the shell's centre, the number of impacts required to reach puncture increases by 10.5% and 21.1% for distances of 20 and 30 mm, respectively. Furthermore, it is also found that alternating impacts between symmetrical points show no inclination towards a preferential point for puncture.