Multi-scale modelling approach to homogenise the mechanical properties of polymeric closed-cell bead foams

Analysis of density-dependent bead and cell structure of expanded polypropylene bead foams from X-ray computed tomography of different resolution

“…A combination of the tool geometry and pressure induced varying bead structure together with the process dependent welding areas between them form the bead foam on the macro-scale with a global structure-dependent density gradient. 5…”

“…A combination of the tool geometry and pressure induced varying bead structure together with the process dependent welding areas between them form the bead foam on the macro-scale with a global structure-dependent density gradient. 5 The knowledge of the distribution of the morphological features, such as wall thickness, cell and bead size, is important for developing realistic numerical foam models and simulation strategies to predict the material behavior during static and, in perspective, cyclic loads in order to understand the fatigue mechanisms in bead foam. One versatile and powerful non-destructive method for digitizing, visualizing and analyzing the three dimensional inner foam structure is X-ray computed tomography (CT).…”

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

“…[1][2][3] Because of their low density as well as the excellent damping and energy absorption capability, they are nowadays used in various sectors like packaging, sporting goods, automotive and construction. Their specific mechanical deformation behavior (see Figure 1) is a result of the hierarchical inner cell structure and its corresponding microscopic deformation mechanisms, which under compression are commonly divided into three regions: [4][5][6][7][8] 1. At small strains, cell wall bending is predominant and leads to a linear region with a comparatively high stiffness (region 1).…”

“…As the morphological properties like cell wall thickness and cell size as well as the described deformation mechanisms are randomly distributed, 4,9 the transitions between the three macroscopically observed stress-strain regions occur gradually. In addition, numerical simulations on closed-cell bead foams showed that the equivalent plastic strain on microscopic scale exceeds the macroscopically applied compressive strain by a factor of 10 easily.…”

Sintering graded foamed beads: Compressive properties

“…For instance, in pure compression loading, it has been observed that the mesoscale morphology of the bead boundaries (as the one observed in Figure 1b) is locally subjected to multi-axial loading. 21,[27][28][29] The complex mechanical behavior governed by the morphological features (at the dual scale) of the foam and the physical properties of the polymer (i.e., crystallinity and orientation) can be exploited by applying the graded foaming technology to bead foaming. Specifically, the foamed structure of the single bead can be designed to fine tune the local response and improve performances in pure macroscopic compression loading.…”