Impact on a model head-helmet system

A numerical finite-element and a corresponding experimental investigation was conducted to study wave transients in an axisymmetric model head-helmet system induced by short-duration impact loading. Two physical systems were examined: (1) a four-component model consisting of a water-filled aluminum spherical shell nesting inside a two-layer hemispherical shell composed of Styrofoam and aluminum and (2) an actual helmet shell filled with an expanding polyurethane foam containing a cadaver head. The response of two other head-helmet systems subjected to sine-squared pulse loadings were also obtained numerically utilizing measured mechanical properties of the constituents.In general, highly satisfactory agreement was found to exist between predicted and experimentally determined strain histories, deviations occurring whenever discrepancies existed between actual and simulated geometry and material properties. Nearly identical levels of strain were measured for the two physical systems tested when loaded by virtually the same impulse in spite of the difference in their characteristics. However, the presence of a frangible covering was found to drastically reduce the pressure levels transmitted to the interior fluid modeling the brain.