On the determination of viscoelastic properties of EPP foam in dependence on pre-strain and loading direction

Understanding the viscoelastic properties of EPP foams is of crucial importance for their use in industrial applications. However, mechanical testing of polymeric foams is challenging due to the difficulties that arise from their morphology. For this reason, here currently available DMA methods using a single drive and a multi-drive rheometer as well as multiple loading directions are investigated in detail. Experimental challenges are highlighted and discussed with regard to foam-specific properties. Special focus is laid on the influence of compressive pre-strain. Based on the results, guidelines to perform reproducible DMA tests on the investigated type of material are derived. In addition, the results give deeper insight into the deformation behavior of bead foams at small strain levels and reveal an early onset of the transition from linear to plateau regime.