Abstract
The Federal Motor Vehicle Safety Standards (FMVSS) 201U regulation requires the head injury criterion (HIC) value to be less than 1000 during upper interior head impact. Polyurethane (PU) foams are often used as countermeasures to reduce the HIC value in view of their good energy absorption capabilities. This safety load case can be virtually analyzed using finite element simulation, where PU foams are typically represented using material models developed from quasi-static compression test data. However, PU foams exhibit rate dependent behavior and hence the material models need to be updated and validated for high velocity impact. The aim of this work was to carry out high speed impact tests on PU foams, update and validate the material model. Digital image correlation (DIC) was used to obtain deformation and strain distribution on surface of the foam during dynamic impact. The parameters of the low density foam material model (MAT 57 in LS-DYNA) viz. the stress strain curve, hysteretic unloading factor and shape factor were optimized. Displacement data from DIC was used to validate the modified MAT 57 material model. An improved test versus CAE correlation was observed with the modified MAT 57 material card.