Regional brain injury response in child occupants during electric two-wheeler collisions: a multi-scenario finite...

Head injuries in child occupants are a primary concern in electric two-wheeler (E2W) accidents. This study aimed to investigate the biomechanical mechanisms driving regional brain injury of pediatric brain responses under complex, multi-stage E2W impact scenarios impact scenarios involving passenger vehicles, specifically sedans. By using a high-fidelity finite element framework, the research focused on delineating the spatial distribution of internal tissue deformation and characterizing the biomechanical decoupling between global head kinematics and localized tissue-level injury risks within the context of sedan-E2W collisions.

A typical car-to-E2W collision was reconstructed based on a real-world case from the China Deep Investigation of Traffic Accidents (CIDAS) database, involving a female toddler occupant. A high-fidelity finite element (FE) model was established, integrating a passenger car, a E2W, and a child occupant model combining a detailed THUMS brain model with a Hybrid III dummy body. A child bicycle helmet model was also employed. A full factorial Design of Experiment (DOE) was conducted with 36 simulation scenarios, evaluating the effects of car speed ($V_0$: 30, 40, 50 km/h), E2W speed ($V_1$: 15, 20, 25 km/h), and seating position (Front vs. Back). Injury risks were assessed using head kinematic metrics, including Head Injury Criterion 15 (HIC₁₅) and Brain Injury Criteria (BrIC), and tissue-level metrics, such as Maximum Principal Stress (MPS), von Mises stress, and shear stress.

MPS was predominantly concentrated in the anterior cerebral cortex (frontal and temporal lobes), driven by direct force transmission through the meninges and falx cerebri. In contrast, high Von Mises and shear stresses were localized in the brainstem-cerebellum junction and deep brain regions. While helmet use reduced HIC₁₅ by 47%, internal shear stress frequently exceeded Diffuse Axonal Injury (DAI) thresholds (8-16 kPa). Notably, front-seated children exhibited more diffuse high-stress regions, with peak shear stress escalating to 22.7 kPa at high speeds. Back-seated children consistently showed higher peak Von Mises stress (up to 25.8 kPa), though the distribution was more localized compared to front-seated occupants. While helmet use significantly reduced the overall risk, 27.8% of scenarios still exceeded the brain contusion threshold (MPS > 0.88), with high-speed impacts (50 km/h) remaining particularly critical at an 83.3% exceedance rate, highlighting the persistence of deep-tissue vulnerability despite standard protection.

Pediatric Traumatic Brain Injury (TBI) in E2W accidents is characterized by a dual-pattern of spatial injury distribution: superficial cortical strain and deep-tissue shear concentration. Seating position significantly modulates the distribution and intensity of these stresses. Current bicycle helmets offer insufficient protection against internal shear and strain, which are governed by the brain's internal architecture and impact kinematics. Future safety standards should prioritize spatially-resolved tissue metrics and region-specific energy management to address the identified vulnerabilities in the brainstem and frontal-temporal cortex.