A concept for mitigating head injury under translational blunt impact

Abstract

This study assesses a bi-layer composite concept for mitigating the severity of injury due to translational blunt impact of an unprotected head at moderately high speeds. The concept comprises crushable foam and a stiff face-sheet on the impacting face. Approximate analytical models for acceleration–time histories of prototypical impact scenarios are used to guide the design. The key design variables probed experimentally are the crushing strength of the underlying foam and the tile size. The efficacy of the composite systems and the foams alone is ascertained through a series of drop impact tests with an instrumented head-form at a representative impact velocity (6.7 m/s, 15 mph), using three commercial viscoelastic foams, with and without face-sheets. The measurements are analysed in terms of five performance metrics: the peak acceleration, the Gadd severity index (GSI), the head injury criterion (HIC), the skull fracture correlate (SFC) and the head impact power (HIP). The experiments demonstrate that, with the addition of a face-sheet, each of these metrics can be reduced substantially (by as much as a factor of two) relative to those of the foam alone. The benefits derive from spreading of contact forces over a larger area of foam by the face-sheet.