Low-velocity impact behavior of sandwich composite structure with 3D printed hexagonal honeycomb core: varying core materials

Additive manufacturing technology is extensively used in aeronautical applications, especially in designing the sandwich composite structures for repair tasks. However, the composite structures are vulnerable to impact loadings because of their exposure to, for instance, loading field carriages, flying debris, and bird strikes. This may lead to crack propagation and ultimately the structural failure. Therefore, it is important to investigate the mechanical behavior of sandwich composite structures under low-velocity impact. In this research, carbon fiber fabric reinforced 3D-printed thermoplastic composite of hexagonal honeycomb cores structures were fabricated with different unit cells (6, 8, and 10 mm) and varying materials (polylactic acid (PLA), PLA-Wood and PLA-Carbon). A drop weight impact test was performed under impact energies (5, 8, and 11 J) to determine the energy absorption performance of the structures whereas the surface morphology was analyzed using a high-intensity optical microscope. Comparing unit cells of materials used, it is observed that the unit cell of 8 mm is the best configuration for lightweight materials with impressive energy absorption capabilities. Under an impact energy of 11 J, the PLA-Wood of unit cell 8 mm shows 9.22 J higher in energy absorption than unit cell 10 mm which is 7.44 J due to intermediate stiffness that resists further deformation. While the filled PLA shows the PLA-Wood material offers better performance in energy absorption capability compared to PLA-Carbon. The PLA-Wood demonstrates 9.22 J more energy absorption for an unit cell 8 mm under an impact energy of 11 J than the PLA-Carbon, which is 8.49 J. This is due to the good compatibility between the hydroxyl groups of the polymer matrix and lignocellulose filler, which translates to better stiffness.