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Composite sandwich structures have gained significant attention in engineering applications due to their exceptional strength-to-weight ratio, stiffness, and energy absorption capabilities. One promising core material is cork, which possesses desirable characteristics such as low density, high compressive strength, and good energy absorption capacity. This study aimed to compare the impact performance of composite shells with composite sandwich shells featuring an agglomerated cork core, while investigating the influence of semicylindrical shell diameters. The results underscore the significant impact of specimen diameter on the performance of these structures. Larger diameter specimens (106 mm) exhibited notably higher maximum force, albeit with lower maximum displacement, energy absorption, and contact time compared to those with smaller diameter (82 mm). Similar trends were observed in composite sandwich shells. Furthermore, the inclusion of cork in composite sandwich shells marginally reduced strength of the specimens. For identical diameters, both configurations exhibited comparable maximum force and displacement. However, composite sandwich shells with a cork core absorbed less energy than those without a cork core. This behaviour persisted across both shell geometries, with slightly higher percentage differences observed in the larger diameter specimens.

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.

Based on numerical modelling, this study investigates asymmetric semicylindrical composite laminate shells' damage characteristics under low-velocity impact loads. For this purpose, several asymmetric stacking sequences were subjected to low-velocity impact and the results were analysed in terms of force, displacement, contact time, and absorbed energy. It is concluded that the maximum impact force decreases with an increase in the number of layers oriented at 0º, particularly in the upper half of the laminate. The laminates with a 45º orientation in the upper layers present the lowest displacement values, whereas the laminates with the upper layers oriented at 0º exhibit longer contact times. It is also observed that intralaminar damage is responsible for almost half of the total impact energy, followed by delaminations and friction. Stacking sequences with upper layers at 45º exhibit slightly higher energy dissipation due to intralaminar damage (fibre failure) and interlaminar damage (delamination).