Volume 3 · Issue 6 (2026)
DOI number:
10.66521/2938-9933-2026061701
Injury Mechanisms of an Unrestrained Occupant in Urban Bus Frontal Collisions Based on a Human Finite Element Model
Kang Li, Shihai Cui*
School of Mechanical Engineering, Tianjin University of Science and Technology, Tianjin, China
Corresponding Author: Shihai Cui
Abstract: To investigate the injury mechanisms of an unrestrained occupant in urban bus frontal collisions, a simulation study was conducted based on a validated THUMS AM50 human finite element model and an urban bus finite element model. A typical seated occupant posture was established, and a frontal collision acceleration-time curve was applied as the boundary condition. The occupant kinematic response and biomechanical injury indicators of the head, neck, and abdominal organs were analyzed. The results show that, during the frontal collision, the occupant moved forward significantly under inertial loading and the head violently impacted the front-row seat, resulting in a high risk of head injury. The HIC15 and 3 ms resultant acceleration of the head center of mass were 915.1 and 96.3 g, respectively, both exceeding the corresponding low-performance limits. The BrIC value was 0.8, corresponding to an approximately 30% probability of AIS 4 brain injury. In addition, the maximum principal strain of brain tissue reached 38.8%, exceeding the injury threshold of 17.7%, indicating a strain-dominated risk of brain tissue injury. In contrast, the cervical von Mises stress, cervical mechanical loads, Nij, and abdominal organ MPS values were all below the corresponding injury thresholds. Therefore, under the frontal collision condition, the primary injury risk for an unrestrained bus occupant is concentrated in the head and brain, while the risks of severe cervical structural injury and abdominal organ injury are relatively low. The findings can provide a theoretical basis for the optimization of bus interior structures and occupant protection systems.
Keywords: Human body finite element model; Urban bus; Frontal collision; Occupant injury; Biomechanics
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