RVE MODELLING OF DEFORMATION AND FAILURE BEHAVIOUR OF CLOSED CELL RIGID POLYMER FOAMS

Closed cell rigid polymer foams are used as light core material in high loadable lightweight sandwich structures. Their mechanical behaviour depends on both the mechanical properties of the constituent solid polymer and the cellular structure on the mesoscopic scale which has therefore to be taken into account for the mechanical characterization of foam materials. This paper deals with the investigation of the deformation and failure behaviour of closed cell rigid polymer foams via numerical representative volume element (RVE) modelling approach. For this purpose the cellular structure of the foam was modelled by a 3d random Laguerre tessellation which was adapted to the real cellular structure of a closed cell Polymethacrylimide (PMI) foam in terms of morphological properties (e.g. cell size distribution) obtained from X-Ray computed tomography (X-Ray CT) data and subsequent 3d image analysis. In addition to the effective linear elastic material properties the strength of the foam model was calculated via finite element analysis (FEA) and consideration of nonlinear failure modes of the cellular structure. Parametric studies revealed the correlation between structural parameters (e.g. foam density, material content in the cell walls etc.) and the effective mechanical properties of the foam. Evaluation of the numerical results was done by standard mechanical testing of foam specimens on the one hand and X-Ray CT in situ deformation experiments with stepwise loading and scanning of foam specimens in a deformed state on the other hand. Both showed the potential of mesoscopic foam modelling with realistic consideration of the cellular structure as well as load case dependent deformation and failure mechanisms for exact prediction of material properties of closed cell foams.