Spinal injury risk assessment of a double-layer cushion for ejection seats based on ABAQUS

Abstract

BACKGROUND: The enormous impact acceleration experienced by the human body during ejection is a major risk factor for spinal injury. Therefore, optimizing the cushioning and energy absorption design of ejection seat cushions is crucial for ensuring the safety of pilots. OBJECTIVE: To construct a human-seat cushion coupled finite element model based on ABAQUS to quantitatively evaluate the impact of a double-layer cushion, which combines the advantages of high and slow rebound, on lumbar spine biomechanical response and spinal injury risk under ejection conditions, and to quantify its safety margin. METHODS: CT imaging data of the entire spine and legs from one male pilot volunteer were selected. Three-dimensional anatomical reconstruction, geometric repair, and finite element meshing were completed to construct a highly biologically faithful digital human model encompassing the entire spine, pelvis, both femurs, and skin soft tissues. A geometric model of the dual-layer seat cushion was also established. Subsequently, a human-chair system coupled model was assembled in ABAQUS. Dynamic simulations were conducted by applying an ejection acceleration time history. Stress responses in the L4–L5 and L5–S1 intervertebral discs were compared between the high-resilience and dual-layer cushion designs. Injury probability was predicted using the Spinal Injury Dynamic Response Index. RESULTS AND CONCLUSION: The simulation results showed good agreement with experimental data, validating the model's accuracy. Performance comparison indicated that, compared with the traditional high-resilience cushion, the double-layer cushion reduced peak stresses in the L4–L5 and L5–S1 intervertebral discs, decreased the Dynamic Response Index by 1.8%, and reduced the spinal injury probability by 10.6%. While meeting relevant limits, it provided a higher safety margin and effectively reduced the risk of spinal injury under ejection impact loads.

1. Introduction

Ejection seats are critical life-saving systems for pilots during emergencies, and their safety directly impacts pilot survival. During ejection, the seat is subjected to high-intensity transient impact loads, causing the human body to experience severe vertical acceleration shocks, particularly compressing the spine and leading to potential injuries. Therefore, enhancing the cushioning performance of ejection seats and optimizing seat cushion structures to reduce injury risk have become important research directions in aviation safety.

Due to the scarcity of real ejection experiments, numerical simulation has been widely adopted for safety verification and mechanism analysis. Early human body models often treated bones as rigid bodies and ignored soft tissue connections, limiting their biofidelity. Recent studies have developed more sophisticated models. For instance, Zheng et al. used multibody dynamics to establish a human spine dynamics model, validated with real seated impact tests. Low et al. proposed a spinal injury prediction model based on multibody systems, using CT parameters from a cadaver to construct the skull-lumbosacral structure with spring-dampers representing intervertebral mechanics. Martins et al. developed various numerical models and compared simulation results with experimental measurements, demonstrating that finite element models can be applied to aircraft seat crashworthiness assessments. Han et al. established an impact test protocol and used DYTRAN software to simulate the dynamic response of ejection seats under impact loads. Xiao et al. developed a biodynamic model of a seated human-ejection seat under vertical impact, studying injury risks to the head, neck, and spine. Voleti et al. simulated the response of a seat-dummy system during pilot ejection, focusing on neck and spine motion and injury risk, using fluid-structure interaction models and experimental validation. Yang et al. built a detailed finite element model to analyze the effects of seat component thickness, slider arrangement, and leg restraint force on ejection seat stability. Huang et al. developed a computational model considering dynamic mass characteristics of the human-seat system, comparing rescue effectiveness with static models. Tan established a simulation model of an ejection seat-dummy system, validated its accuracy, and performed sensitivity analysis and orthogonal optimization to improve stability.