Impact performance criteria employed in the evaluation of protective headgear often consider the temporal characteristics of the translational acceleration induced in the helmeted headform during impact. These implicit criteria may appear as limits on the time during which the test headform acceleration is allowed to exceed certain values, or may be inherent in the pass/fail criterion itself.
The present study examines the significance of time as a parameter in the prediction of head injury likelihood or severity. It is shown that since the temporal characteristic of the acceleration waveform is simply a reflection of the mechanical characteristics of the headform/helmet assembly it bears only a trivial relation to the input forcing function and thus is generally uncorrelatable to head injury severity.
It is concluded therefore that an upper limit on translational acceleration alone, though not without certain restrictions, constitute a sufficient criterion for evaluating helmet performance. The use of a time related parameter is shown to be unsupportable and can lead to unnecessarily complex criteria and inferior helmet performance. This paper was formerly presented at the AGARD AMP Specialists Meeting, Cologne, Germany, April 26–28, 1982.