Pulse Shape and Duration in Frontal Crashes

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Pulse Shape and Duration in Frontal Crashes

Crosby, Charles L. / Warner, Charles Y. / Warner, Mark H. / Armstrong, Michael J.

Understanding of events within the history of a crash, and estimation of the severity of occupant interior collisions depend upon an accurate assessment of crash duration. Since this time duration is not measured independently in most crash test reports, it must usually be inferred from interpretations of acceleration data or from displacement data in high-speed film analysis. The significant physical effects related to the crash pulse are often essential in reconstruction analyses wherein the estimation of occupant interior “second collision” or airbag sensing issues are at issue.A simple relation is presented and examined which allows approximation of the approach phase and separation phase kinematics, including restitution and pulse width. Building upon previous work, this relation allows straightforward interpretation of test data from related publicly available test reports. The relation constitutes a closed-form model called BSAN, which represents the entire crash pulse by the specification of five readily available reconstruction parameters: closing velocity, approach time, maximum crush, coefficient of restitution, and total contact time. Of these, all but the time estimates are generally part of a normal crash reconstruction process. Relationships between the pulse shape, the “characteristic length” (or the “centroid time”) for a pulse representing a typical structure and test condition are explored as a means for improving time parameter estimates. Data from various crash tests of similar structures are compared to show examples of the selection of test parameters and applications of the estimation process. In representation of essential crash kinematics the BSAN model is shown for the test cases investigated to be manifestly superior to the rectangular, triangular, half-sine, and haversine approximations often used to represent the crash pulse.