A 3D printed accordion cellular structure with morphing behavior is proposed as the core of sandwich structures to absorb out-of-plane indentation loading. Accordion cellular cores with their high bending stiffness and close-to-zero Poisson's ratio can be used in morphing wing applications to sustain static and impact loadings. These structures are highly tended to be employed in aero-space applications where the collision of foreign objects is inevitable. Hence, their out-of-plane response against indentation loading as well as their ability to absorb energy should be assessed. In this study, 3D printed accordion cellular lattices of Polylactic acid (PLA) with/without glass fiber reinforcement are employed as the core of the sandwich panel. The raw 3D printed cores are then cut so that the numbers of straight and curved walls are identical (balanced core) or different (unbalanced core). Quasi-static indentation tests are con-ducted on the sandwich panels of the unbalanced/balanced cores with both pure PLA and glass fiber-reinforced material. The experimental results proved that having a balanced core configuration can increase the specific energy absorption of the sandwich panel by a factor of 1.7. It is also revealed that the sandwich panels with balanced configuration cores of glass fiber reinforcement PLA material exhibit 150% more specific energy absorption in comparison with those of an unbalanced unreinforced core.
