Head Excursion of Seat Belted Cadaver, Volunteers and Hybrid III ATD in a Dynamic/Static Rollover Fixture 973347

In rollovers, belted occupants sustain a lower fatality rate compared to unbelted occupants primarily due to lower risk of partial or full ejection. However, seat belt and occupant compartment designs found in most current vehicles do not prevent head contact with the vehicle interior during a rollover because of occupant torso and head excursion that result from the rollover dynamics. An experimental study was conducted to simulate the airborne phase of a rollover. The goals of this study were to: 1) quantify the effect of restraint anchor locations and belt component designs in reducing head excursion, and 2) to better correlate the response between humans and an Anthropomorphic Test Device (ATD) during the high angular roll rate of the airborne phase of a rollover.

A Head Excursion Test Device was designed to rotate a restrained occupant about an axis to approximate the inertial loading experienced during the airborne phase of a rollover. Overall occupant kinematics were recorded with onboard video cameras and analyzed to determine vertical and lateral head displacements. Static tests were carried out using human volunteers, and both static and dynamic tests were conducted with a Hybrid III ATD and a human cadaver. In addition to the test subject, webbing length and angle, latch plate design and restraint pretensioning were used as control variables for evaluation of head excursion.

A total of 80 excursion tests were conducted: 51 tests with a Hybrid III 50th percentile male ATD (20 static and 31 dynamic), 18 tests with a cadaver (7 static and 11 dynamic) and 11 static tests with two male volunteers. In tests using a two-point lap belt, belt angle was more significant than overall belt length in reducing head excursion. Results indicated that vertical head excursion was minimized with a steep lap belt angle and short webbing length. Tests utilizing a three-point lap and torso restraint demonstrated that the torso belt reduced vertical head excursion primarily by restricting forward torso rotation. Furthermore, increasing the belt webbing pretension load reduced vertical and lateral head excursion. Comparison of results from human volunteers, cadaveric and Hybrid III ATD subjects in static tests indicated that the Hybrid III ATD had the least vertical excursion. Dynamically, the Hybrid III ATD had less vertical and lateral excursion than the cadaver.

Results from this study may be useful in future seat belt design. Results also suggest that while the currently available Hybrid III ATD is a useful tool in testing the effectiveness of restraint system parameters, it may not fully simulate vertical and lateral head excursion of humans in rollover conditions.