Transverse Anisotropic Modeling of Honeycomb Extruded Polypropylene Foam in LS-Dyna to Optimize Energy Absorption Countermeasures

To meet automotive legal, consumer and insurance test requirements, the process for designing energy absorption countermeasures usually comprises Finite Element simulations of the specified test. Finite element simulations are used first to see if there is a need for an Energy Absorption countermeasure at all and if so, what type, material and shape. A widely used class of energy absorption countermeasures in automotive interior applications is honeycomb extruded polypropylene foams (HXPP). Under compression, these foams exhibit a constant plateau stress until late densification. This enables these foams to minimize packaging space for a given amount of energy to be absorbed or maximize energy absorption for a given packaging space. Robust and easy to use isotropic CAE material models have been developed for HXPP, however the true material properties are anisotropic and such a material model could be necessary in some cases. This paper describes how HXPP can be modeled as a transversely anisotropic material model in LS-DYNA3D (material model number 142). Testing on samples to determine dynamic compression curves under various strand angles and the resulting material property cards are described and an example of a strand orientation optimization for a knee impact situation is given.