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An algorithm for calculating the Head Injury Criterion (HIC) from a digital record of the resultant head acceleration of a dummy used in impact testing is described. A result from Chou and Nyquist (1) is used to establish a procedure for searching the range of time intervals within the acceleration pulse which should guarantee finding the true HIC. A second result from the same authors is used to make the search far more efficient for most head acceleration records. The algorithm is implemented in a simple way which does not require curve-fitting or interpolation between the data points. This algorithm, implemented as a computer program, has been tested with head acceleration records from impact tests with dummies and some results are given. 1. C. C. Chou and G. W. Nyquist, “Analytical Studies of the Head Injury Criterion.” Society of Automotive Engineers, Automotive Engineering Congress, Detroit, MI, U. S. A., Feb, 1974. (SAE Paper No. 740082)

A set of digital and analog low-pass filters, which meet specific data-processing criteria for impact testing, are described. The design, implementation and performance of the filters are discussed. These digital filters exhibit finite-impulse- and linear-phase-shift response characteristics. They were designed using the Remez exchange algorithm. The active analog filters, which exhibit a near linear, phase shift, Bessel response, were developed using commercially-available integrated circuits. These filters have the frequency-and channel-class characteristics advocated by the Society of Automotive Engineers in their publication “S.A.E. Recommended Practice J211b, Instrumentation for Impact Tests”.

The data acquisition system for impact testing at the Defence and Civil Institute of Environmental Medicine (DCIEM) uses a set of 49 Datalab recorders. Each of these recorders converts an analog transient electrical signal into digital form at sampling rate up to 200 kHz and stores 4096 samples for subsequent transfer to a computer. Data processing and plotting of results, including resultants and severity indices, is completed within 40 minutes of a test. The system offers a speed and versatility far superior to alternative systems using analog FM magnetic tape recorders.