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The effect of geometry and fracture on the energy absorption of polymeric foam
A new design protocol and energy absorption models are proposed for polymeric foam that improve material and absorber geometry selection for impact conditions encountered in service. Design diagrams are constructed that show the energy absorption of uniaxial and trapezoidal absorber geometries as a function of product geometry, foam density, and strain rate for closed cell polyethylene (PE) and polystyrene (EPS) packaging foams. Design constraints including load spreading, buckling, creep, and material costs are addressed. Energy absorption models for plate, cylindrical, and spherical product geometries generate design data that account for the increased stress and energy absorption resulting from deformation of foam adjacent but external to the region directly below the product (i.e., load spreading). The models partition the energy absorption into polymer deformation and gas compression components, require only easily obtainable uniaxial compression data, and agree within fifteen percent of measured values. Additionally, a systematic examination of the effect of processing parameters on EPS fracture and energy absorption characteristics addresses the influence of cracks frequently observed in impacted commercial EPS components. The energy absorbed during compression increases with increasing toughness because compression induced fracture is reduced. Lower fracture toughness allows longer cracks, which decreases the energy absorbed, possibly resulting in damage to the packaged product. The toughness increases as a function of increased molding time and pressure because of increased fusion. Fusion is characterized by quantitative fractography and is correlated with toughness.
Stupak, Peter Raymond, "The effect of geometry and fracture on the energy absorption of polymeric foam" (1992). Doctoral Dissertations Available from Proquest. AAI9305903.