Investigation on Energy Absorption Properties of CNTs/Al–Cu–Mg Composite Foams Based on Split Hopkinson Pressure Bar Test and Constitutive Model

The potential of carbon nanotubes (CNTs) was investigated as reinforcements to enhance the deformation behavior and energy absorption of composite foams (CFs) under high strain‐rate impact (over 100 s −1 ). Split Hopkinson pressure bar (SHPB) tests were performed at 650 and 1300 s −1 to characterize the dynamic compressive properties of closed‐cell CNTs/Al–Cu–Mg foams with 0, 0.25, and 0.5 wt.% CNTs. The foams exhibited notable strain‐rate sensitivity, mitigated by CNT addition. Compared with the unreinforced foam, the 0.25 wt.% CNTs foam exhibited optimal energy absorption capacity, with a 29% improvement (from 1.63 to 2.11 MJ/m 3 ) at 650 s −1 and a 22% enhancement (from 3.59 to 4.39 MJ/m 3 ) at 1300 s −1 . Correspondingly, its strain rate sensitivity coefficient was reduced by 60% (from 0.05 to 0.02) and 68% (from 0.11 to 0.035) under the two strain rates, respectively. By contrast, the 0.5 wt.% CNTs foam showed deteriorated mechanical performance, which can be attributed to CNT agglomeration that weakened the interfacial bonding between CNT fillers and the matrix. A simplified Sherwood–Frost (S–F) constitutive model was established to accurately calibrate the stress–strain responses and energy absorption. Furthermore, the strengthening mechanisms, including effective load transfer and grain refinement, were revealed via fracture morphology analysis.