Energy absorption mechanism of aluminum foam sandwich structure against bird impact and its application in impact protection bulkhead inside airplane nose

In response to the insufficient lightweight issue of the baffle plate for the nose end frame with an aluminum alloy stiffened structure in active civil aircraft, a new type of aluminum foam sandwich baffle structure is proposed based on an in-depth exploration of the energy absorption mechanism of aluminum foam sandwich structures against bird impact. This innovative design employs an asymmetric panel configuration that includes a highly ductile 2024-T3 aluminum alloy upper face sheet, a high-strength 7075-T6 aluminum alloy lower face sheet, and an aluminum foam core layer in between. It replaces the traditional aluminum alloy stiffened panel, aiming to significantly reduce structural weight while ensuring excellent bird strike resistance. First, the effectiveness of the bird body constitutive model and its contact algorithm was verified by comparing the high-speed bird body impact test on aluminum alloy flat plates with the simulated strain data. Based on previous experimental data, combined with parameter inversion and simulation cases, the simulation data of homogeneous and gradient aluminum foams are in good agreement with the test results, which verifies the accuracy and applicability of the aluminum foam material constitutive model. Furthermore, using the professional Pam-crash software, transient impact dynamics simulations of bird strikes were conducted on both the stiffened panel structure and the aluminum foam sandwich structure end frame. Combined with the damage and deformation conditions of each component and energy absorption data, a comparative analysis was made on the differences in their impact response characteristics and energy absorption mechanisms. The study shows that the stiffened panel mainly absorbs the energy of bird body impact through its plastic deformation, while the aluminum foam sandwich structure absorbs energy synergistically through the compressive collapse failure of the core layer and the large plastic deformation mechanism of the upper face sheet. The optimized aluminum foam sandwich structure is significantly superior to the traditional stiffened panel structure in terms of energy absorption efficiency. Subsequently, a full-coverage optimization design scheme for the baffle was completed based on the energy absorption characteristics of the aluminum foam sandwich structure. According to the full-coverage bird impact simulation results, the proposed aluminum foam sandwich baffle design achieves a structural weight reduction of more than 30% while maintaining the same bird strike resistance performance as the in-service structure. This research provides reliable technical references and innovative ideas for the lightweight bird strike-resistant design of the civil aircraft nose bulkhead.