Understanding the Effects of Age and Safety Countermeasures on Occupant Kinematics in Low-Acceleration, Time-Extended Events

A significant role of safety countermeasures and vehicle restraints is to minimize contact between the occupant and vehicle interior; thereby significantly reducing the risk and incidence of injury. Current testing protocols evaluate restraint performance with an optimally positioned ATDs or HBMs (e.g., seated upright against the seat back, gaze forward and hands on the lap); however, occupant position may be influenced by pre-crash maneuvers. Low-acceleration time-extended (LATE) events, such as evasive swerving, often precede a crash event. The inertial forces during LATE events have the potential to cause changes to the occupant's initial state (initial posture, position, muscle tension). Evasive swerving can displace occupants away from idealized seating positions and may induce bracing or muscle tensing as inherent reaction strategies. In turn, the occupant's pre-crash state may compromise the restraint system's performance and its contribution to occupant protection during the crash phase. Common out-of-position or sub-optimal positions and the injury risks associated with them have yet to be determined. In addition, the level of restraint robustness to accommodate changes in occupant size and state remains largely unknown. Hence, it is imperative to study occupant kinematics during pre-crash events because the optimal performance of restraint systems requires an accurate assessment of the pre-crash position of the occupant. Developmental differences that occur between adolescence to adulthood may also affect occupant kinematic responses. Therefore, the objective of this study is to quantify the kinematic response of restrained pediatric, young adult and adult human volunteers during a simulated evasive swerving maneuver and evaluate the effects of age, two safety countermeasures (e.g., pre-pretensioning and inflated torso bolsters), and muscle response, on occupant kinematics. This research was approved by the Children's Hospital of Philadelphia and Drexel University Institutional Review Boards. A novel laboratory device was custom constructed for this study to expose human subjects to non-injurious loading conditions that mimic real-world evasive swerving events. A comprehensive meta-analysis was conducted to determine the appropriate oscillatory acceleration and magnitude that is safe for human subject testing and also representative of dynamic pre-crash field data. The acceleration pulse was determined to be safe and repeatable and exposed subjects to oscillatory peak lateral accelerations of 0.72 ± 0.04 g. Healthy male subjects were selected such that they resembled the broad range of occupant ages and sizes found in the second-row passenger seat of a motor vehicle. In total, 40 male human volunteers, ages 9-11 years (n=10), 12-14 years (n=10), 15-17 years (n=10) and 18-40 years (n=10), were tested. Each subject was exposed to a series of test conditions (relaxed, braced, pre-pretensioned seat belt, sculpted vehicle seat with and without inflated torso bolsters) while their kinematics were captured using 3D motion‐capture and muscle activity was recorded. The implementation of a pre-pretensioner, otherwise known as a reversible motorized seat belt, was an effective vehicle countermeasure during a simulated evasive swerving maneuver as it substantially reduced lateral head and trunk displacement as well as limited transverse trunk rotation by approximately 50%. Kinematic differences were observed across the subsequent cycles of the test; the first cycle, likely representing an unaware occupant, experienced the largest lateral displacement, despite having the lowest lateral acceleration. Bracing was studied as a volunteer induced countermeasure, and it significantly reduced peak lateral head and trunk displacement by approximately 40%, independent of age. Analysis of the mean muscle response aligned with the resulting kinematics. These results suggest that the occupants employ various neuromuscular strategies to counteract motion as they become more aware of the loading condition. Last, some subjects employed transverse trunk rotation during the cyclic maneuver; however, this kinematic strategy did not have age-specific implications. Findings from this data set can help guide the implementation of safety countermeasures that are relevant to the pre-crash phase. Additionally, acquisition of such data, which includes a broad range of occupant ages and sizes, is essential for the validation of computational human body models and anthropomorphic testing devices. Although such data has an automotive focus, this research emphasizes the study of biomechanics is at the interface of active and passive safety.Ph.D., Biomedical Engineering -- Drexel University, 201