Biomechanical evaluation of a dual-layer cushion for pilot ejection seats: Full-scale dummy tests and finite element...

Spinal and neck injuries are major biomechanical concerns during pilot ejection, particularly under high vertical acceleration. As the main load-transfer interface between the seat pan and the occupant, the cushion affects how impact loads are transmitted to the body. This study evaluated a dual-layer cushion consisting of an N3 slow-recovery contact layer and an N1 high-rebound support layer at a thickness ratio of 2:1, with a single-layer N1 cushion as the reference. Full-scale vertical dummy ejection tests at 10 G and 14 G were used to assess dynamic responses of the spine and neck. A CT-based human-cushion finite element model was also used to analyse static interface pressure and local spinal responses under a representative high-acceleration condition. Compared with the reference cushion, the dual-layer cushion reduced $\mathrm{DRI}$ by 17.6% at 10 G and 7.3% at 14 G, while also reducing the resultant forces and $N_{\mathrm{ij}}$ values in the upper and lower neck. At 14 G, upper- and lower-neck $N_{ij}$ decreased by 19.9% and 27.6%, respectively. The finite element results further showed reductions of 13.1% and 14.5% in peak stress at the L4-L5 and L5-S1 intervertebral discs, respectively. These results indicate that layered cushion materials can alter impact-load transmission at the human-seat interface and reduce biomechanical responses associated with spinal and neck injury. The dummy tests and human finite element analysis provide complementary evidence at the whole-body dynamic and local tissue-mechanical levels for evaluating the biomechanical protection of the dual-layer cushion.