The Head Injury Criterion (HIC) in FMVSS 208 for evaluating the potential head injury requires maximisation of a mathematical expression, involving the time-average acceleration, by varying the limits (t 1, t 2) of the time interval over which the average is calculated. This paper describes the HIC behaviour through the analysis of a function of two independent variables t 1 and t 2. The analysis is carried out for any arbitrary acceleration profile a(t). It is found that maximisation requires that a(t1)=a(t2). Also, for the unique values of t 1 and t 2 that maximise HIC, the average acceleration between t 1 and t 2 is 5/3 times the acceleration at t 1 or t 2. Illustrative examples are provided by applying this condition to simple pulses. Numerical results are presented in tables and graphs.
Samenvatting