Simplified MADYMO Model of the IHRA Head-form Impactor

Interest in pedestrian head injury has prompted a need to measure the potential of head injury resulting from vehicular impacts. A variety of head impactors have been developed to fulfill this measurement need. A protocol has been developed by the International Harmonization Research Activity (IHRA) to use head impactor measurements to predict head injury. However, the effect of certain characteristics of the various head impactors on the measurement procedure is not well understood. This includes the location of the accelerometers within the head-form and testing the head-form under the variety of conditions necessary to establish its global performance. To address this problem, a simple model of the IHRA head-form has been developed. This model was created using MADYMO© and consists of a solid sphere with a second sphere representing the vinyl covering. Stiffness and damping characteristics of the vinyl covering were determined analytically from drop test data of an IHRA head-form. The model was validated by comparing its response to a drop test of 0.5 meters onto a steel plate. The results show that the model is an effective, simple solution to evaluating an IHRA impactor. The results also indicate that a more complete description of the vinyl covering (i.e., finite elements) would be appropriate for certain impact configurations.