Energy absorption characteristics of polymeric foams used as cushioning materials

Abstract

The "Efficiency of Energy Absorption" (or "Efficiency") and "Ideality" parameters were evaluated for several plastic foams and were found to be very useful in choosing a n appropriate cushion for the protection of a specific product. The maxima in these parameters were found to be in the same range of stresses, when derived from dynamic measurements or from predicted stress-strain curves based on previously proposed "Reference" and "Modified Boltzman Superposition" Models. For the rate independent foams the maxima in these parameters do not change with strain rate and can therefore be derived from slow, constant rate ("static") experiments. For rate dependent foams however, the maxima from "static" measurements were found to be in a lower range of stresses than those derived from dynamic ones. As a result, slow rate compressive measurements do not predict well the behavior of the foams during impact and the use of the "Reference" and "Modified Boltzman Superposition" Models is required for good predictions. It was found that the stiffer PS and PE foams attain maximum Efficiency and Ideality at higher stresses than the more flexible PUR foams.

An investigation into reinforced and functionally graded lattice structures

“…The determined values of the parameters discussed above are provided in tables 3 and 5. ε D were determined using the energy efficiency method outlined by Miltz and Ramon 25 and Li et al 26 The BCC z lattices, with their additional cellular reinforcing struts in the z direction, provided higher modulus and plastic collapse strength than the BCC lattices. Their modulus and plastic collapse strength were around 220% and 41% larger, respectively, than those of the BCC lattice when the compressive load was applied in the z direction.…”

3D printed polyurethane honeycombs for repeated tailored energy absorption

“…The mechanics of hexagonal structures are well understood and their deformation behaviours under different loading conditions have been established via mechanical models [19,20]. At low strains, the cell walls of a regular hexagonal array loaded in either the transverse and ribbon direction will deform by bending as illustrated in Figure 6a and 6b respectively [21].…”

“…There exists a compression energy to which any uniform-density cellular structure is uniquely optimised, and identifying this is one of the methods for quantifying the energy absorbing capability and efficiency of a cellular structure; applying this analytical methodology to 3D printed constructs permits unique tailorability of the response to the environmental loading. From a designers point-of-view, the stress-strain diagrams for each 3D printed structures will generate energy absorption and efficiency diagrams which can be employed as part of a designer's toolbox to characterise the energy absorbing potential of cellular structures [18,19].…”

3D printed elastic honeycombs with graded density for tailorable energy absorption

“…At intermediate energies however, the uniform array is significantly more efficient at absorbing compressive energy. In order to better interpret the efficiency of these structures over a range of compression energies, efficiency diagrams can be formed by dividing the cumulative energy by the instantaneous stress [3].…”

“…The Optimum energy absorption envelope can be drawn that passes through the shoulder points for cellar structures formed from the same material, with increasing density. The Efficiency of such structures at absorbing a range of impact energies can then be defined by dividing the energy absorbed by instantaneous stress [3] as shown in Figure 2b.…”