oa Characterization And Mechanical Performance Of Ultralight Metallic Lattice Core Composite Sandwich Shell

In this study sandwich-walled cylindrical shells with aluminum pyramidal truss core of constant curvature suitable for functional applications were fabricated employing an interlocking fabrication technique for the metallic core. The skins were made of carbon-fiber reinforced composites and co-cured with the metallic truss core. Thereafter, axial compression tests on some representative samples were carried out to investigate the failure modes of these structures and compared with an analytical failure map developed to account for Euler buckling, shell buckling, local buckling between reinforcements and face-crushing. The experimental data closely matched the analytically predicted behavior of the cylinders. In particular, it was found that local buckling and face crushing modes can exist together and are the most important modes of failure of the fabricated structure. In addition, a study on the bending response of semi-cylindrical samples is also presented using a combination of analytical modeling, three-point bending experiments and finite element (FE) based simulations. The aluminum pyramidal cores of these samples were also constructed using the novel interlocking method before curing them with composite face sheets to fabricate the final structure. A theoretical model was developed to analyze the experiments and develop failure criteria. Three failure modes: i) Face wrinkling, ii) Face crushing, and iii) Debonding between face sheet and truss cores, were considered and theoretical relationships for predicting the collapse load associated with each mode were developed. The experiments were carried out on two sets of specimens with differing face sheet thickness which clearly indicated the important role played by core debonding in determining the peak load of the structure. Localized buckling instabilities were also reported for samples with thinner face sheets. The role of debonding in determining strength was further highlighted by a comparison with FE simulations with suppressed debonding. This study highlighted the superior structural performance and failure properties of these structures thus demonstrating their suitability for their integration into the next generation of ultralight multifunctional systems.