Characterization of Energy Absorption and Strain Rate Sensitivity of a Novel Elastomeric Polyurea Foam

Abstract

Elastomeric polymer foams are widely used in sports and other protective padding applications due to their unique properties, such as excellent cushioning and relatively high‐energy absorption to weight ratio. This work investigates the mechanical and energy absorption performance of an elastomeric hybrid structure polyurea foam in response to low‐velocity impact. The examined polyurea foams are synthesized using a novel self‐foaming process that leads to the development of a semi‐closed cellular structure. The quasi‐static response of the foam is first characterized by measuring the global stress–strain and energy absorption characteristics. The evolution of the foam's Poisson's ratio is also characterized by in situ digital image correlation (DIC) measurements. The same properties are also studied in dynamic loading conditions by subjecting the foam samples to controlled impact tests. A strain‐dependent rate sensitivity parameter is used to quantify differences between the quasi‐static and dynamic strength and energy absorption responses of the foam. The examined foam shows significant enhancement in strength at increased strain rates while retaining its excellent energy absorption capacity. This unique characteristic of the examined foam is discussed in terms of the concurrent effects of entrapped gas and the rate sensitivity of the parent polymer.

Mechanics of Microspheres Reinforced Hollow Microcells

“…Over the range of investigated load application regions, only two buckling modes are observed, those starting at 2α = 16 deg and 2α = 23 deg, which is mechanistically consistent with the results of the considered boundary conditions and shown experimentally by Shorter et al [7]. Such elastic deformation is highly desirable in polymeric foams because (1) it signifies recoverable deformation where the foam padding can sustain repeated loading (recently demonstrated experimentally by our group [13]), and (2) it implies large energy dissipation due to buckling to shunt the energy protecting human brains from a concussion in biomechanical impact scenarios [14].…”

Tuning the Mechanical Behavior of Density-Graded Elastomeric Foam Structures via Interlayer Properties

“…Dynamic testing of the graded foam stacks was carried out using an instrumented drop weight tower (Figure a) by dropping a 723 g impactor from a height of 1000 mm. The utilized impact conditions subjected the graded samples to a nominal strain rate of ∼120 s –1 , determined based on the impact velocity (discussed in refs and ) and the original length of the foam stacks (∼37 mm). The transmitted impact force–time history was recorded using a sensor placed below the foam sample, which was then used to analyze the dynamic response of graded foam stacks.…”

“…The recorded images were postprocessed using the commercial DIC software Vic-2D (Correlated Solutions Inc., SC, USA) with subset, step, and strain filter sizes optimized for each case. The DIC parameter optimization process has been reported in detail in refs and .…”

“…The present study examines the role of interface adhesive properties on the mechanical response of bilayer density-graded polyurea foam structures. In recent years, polyurea foam has attracted a good amount of interest due to its hierarchical cellular network and semiclosed cellular structure in impact mitigation applications. ,, Polyurea shows an extended plateau area in stress–strain response. , The mechanical characterization of polyurea foams demonstrates a superior characteristic under both quasi-static and dynamic loading conditions. ,, The outstanding mechanical performance of polyurea foam under different loading conditions distinguishes it from other elastomeric cellular solids. , …”

Scalable Fabrication of Microcellular Open‐Cell Polymer Foams

“…If the cells are completely devoid of cell walls, this type of open-cell foams can further be classified as reticulated foams. [1][2][3] Open-cell foams are porous, tortuous and permeable; they can be used in a variety of applications including energy absorption, [2][3][4] airborne sound absorption, [5,6] selective extraction, [7,8] and membrane. [9] When made with biodegradable and/or biocompatible materials, open-cell foams may also be used as bioscaffolds and drug-delivery carriers.…”