Experimental study and finite element analysis on energy absorption of carbon fiber reinforced composite auxetic structures filled with aluminum foam

Aluminum foam (AlF) and carbon fiber reinforced polymer composite (CFRP) are used in making lightweight energy-absorbing components (EACs) due to their excellent energy absorption (EA) and specific energy ab-sorption (SEA) properties. Auxetic structures (AUS) have a negative Poisson's ratio effect (NPRE), which are expected to exhibit high energy absorption and fracture resistance. To explore the combined effects of material and structural advantages, honeycomb re-entrant AUS made from CFRP prepregs were filled with (closed-cell) AlF. The compressive properties, EA and SEA of the resulting cell structure, AlF-CFRP-AUS, were investigated by quasi-static loading experiment for three different AlF fillings (namely, in full space, in internal space and no filling) and at the respective three orthogonal loading directions (namely, In-Plane Transverse (IPT), In-Plane Longitudinal (IPL) and Out-of-Plane Normal (OPN)) with respect to the honeycomb structure. The experi-mental results were completed by predictions from finite element models of the AlF-CFRP-AUS. The results show that the CFRP-AUS filled with AlF exhibited enhanced elastic modulus, initial peak load, nominal plateau stress, EA, and SEA in the respective IPT and IPL directions. However, no appreciable enhancement was observed in the OPN direction. In the IPT and IPL directions, the enhanced SEA of the AlF-CFRP-AUS was attributed to the combined effects of material and structure and NPRE. For the internally filled and fully filled structures in the IPL direction, based on the unfilled structure, the benefits of SEA and elastic modulus exceed 114 % and 190 %, 340 % and 477 %, respectively. All cells in the honeycomb AlF-CFRP-AUS exhibited similar deformation response during loading; the deformation and collapse of a single cell could cascade to the rest of the cells. These results suggest that the AlF-CFRP-AUS configuration could be potentially useful for the design of lightweight EAC.