Analysis of Density-Dependent Cell Structure of EPP Bead Foams Under Compression

Abstract Background Closed cell polymer bead foams are widely used in industrial applications due to their extraordinary damping and insulation properties. To understand the structure-property-relations at different deformation states the volumetric structure of polymer walls, cells and beads should be statistically analysed. Objective The presented work is focused on the statistical analysis of the changing cell structure of expanded polypropylene bead foams of different density at distinct compression states. Methods Cylindrical bead foam specimens are scanned by x-ray computed tomography at 3-5 different compression states. The reconstructed volume information is segmented and statistically analysed. Results It could be shown that, among others, the cell sphericity and their orientation relative to the plane normal to the loading direction are sensitive parameters to the deformation state. With regard to the material symmetry level, a shift of the isotropic foam to transversal isotropic structure was observed. No sudden, stability related, deformation or failure could be observed. Conclusions Good metrics for the deformation analysis of expanded polypropylene bead foams from in-situ computed tomography tests are the cell sphericity and orientation. Compression deformation leads to a gradually change of material symmetry level from isotropy to anisotropy.