Testing in order to measure the protection against impact of people, manufactured items, and agricultural produce: How to consider all severities of shock

Abstract

Instrumented headforms are projected at cars to check that the vehicle is not overly injurious if a pedestrian is struck. We argue that there are at least two different aspects to performance: the impact severity in the test conditions (measured by HIC, the Head Injury Criterion), and the speed at which bottoming out occurs (this refers to the vehicle surface deforming sufficiently that the much more rigid structures underneath are contacted). It is desired to know performance over the wide range of real-life impact conditions, yet the number of tests to be conducted is limited. A procedure is proposed that estimates performance averaged over different speeds (and perhaps also averaged over effective head mass). There are three components: (a) an equation for the dependence of HIC on speed (and perhaps mass), which includes the effect of bottoming out as a sharp rise in severity beyond a certain level of impact energy, (b) an equation for how bad are different levels of HIC (the probability of some specific outcome, such as death or skull fracture, is likely to be used here), and (c) the probability distribution of impact speed (and perhaps mass). Other safety tests (such as impact testing of helmets) are plainly analogous, and similar considerations apply in the packaging and handling of manufactured items and agricultural produce: cushioning should be soft enough not to cause damage itself yet stiff enough to prevent bottoming out.