Initial Adaption of the Injury Risk of the Human Leg Under High Rate Axial Loading for Use with a Hybrid III

Hybrid III Anthropomorphic Test Devices (ATDs) are widely used in testing of military vehicles against Under Body Blast. The relationship, however, between the axial load through the lower leg of the Hybrid III and that through the human tibia has not been quantified. This paper describes a transfer function that relates the measurement from the lower tibia load cell of a booted Hybrid III to the axial force in a post mortem human subject (PMHS). By incorporating this transfer function into an existing injury risk function, a prediction of the likelihood of fracture within the human leg can be obtained from the Hybrid III data. By changing the values of the coefficients within the transfer function to those derived using the maximum error, rather than the average, conservative predictions of probability of fracture can also be obtained. The transfer function is based on a combination of published experimental data, new experiments, and computational modelling. This imposes limitations on the applicability of this prediction process and its accuracy: the time to peak axial force must be less than 10 ms; the accuracy of the prediction depends on the veracity of the PMHS lumped-parameter model used, and the predictions are only truly applicable to the specific boot used in this study. This tentative prediction process indicates that the 10% probability of fracture for a 55 kg female under 40 years old and for an 85 kg male under 40 years old wearing a desert combat boot is related to forces measured by the lower tibial load cell of a Hybrid III wearing the same boot of 7.2 and 11.7 kN, respectively. The transfer function suggested here is the best tool to date for interpreting Hybrid III leg forces into risk of injury to the human leg.