Density‐Dependent Impact Resilience and Auxeticity of Elastomeric Polyurea Foams

Youssef, George; Kokash, Yazeed; Uddin, Kazi Zahir; Koohbor, Behrad

doi:10.1002/adem.202370001

Cited by 2 publications

(2 citation statements)

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“…Namely the former is classified as semiclosed cells with perforations and microsphere reinforcements, while the latter is closed cells with nearly uniform diameters. [ 5,21,22,33,34 ] Notably, the dynamic stress–strain curves of polyurea foams reveal rapid transition into the plateau region, delayed densification that further extended the plateau region, and enhanced the overall dynamic performance. An elaborative discussion about the difference between the dynamic and quasistatic behavior of conventional and density‐graded polyurea foams is included in forthcoming reports by this group.…”

Section: Resultsmentioning

confidence: 99%

Full‐Field Analyses of Density‐Graded Elastomeric Foams Under Quasistatic and Impact Loadings

Smeets,

Kauvaka,

Uddin

et al. 2023

Adv Eng Mater

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Density‐graded elastomeric foams are emerging as effective protective structures to guard humans against mechanical loading. This research investigates the deformation of ungraded and graded foams under quasi‐static and impact scenarios using digital image correlation (DIC). The graded samples were assembled using two interfacing strategies (seamless and adhered), leveraging the adhesiveness of the foam slurry and bulk polyurea, respectively. Deformation mechanisms, including the effect of the interface type on strain transduction and localization in density‐graded structures, are imperative for improving the impact efficacy of protective paddings. Cuboid foam plugs were subjected to quasi‐static and impact loading while recording the corresponding deformation for DIC analysis. The DIC results were separated into three case studies based on the number of layers (1, 2, and 3). The interface effect on the overall mechanical performance of polyurea foam was revealed from the bilayer, mono‐density samples, showing drastic differences between the deformations within each layer. Seamless interface samples exhibited greater compliance than their adhered counterparts in the bilayer density‐graded configurations. Trilayer‐graded foams broadened strain‐time history, extended the impact duration, and reduced strains. This research substantiates the importance of interfacing and gradation strategies on the mechanical response of elastomeric foams as a function of strain rate.This article is protected by copyright. All rights reserved.

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Section: Resultsmentioning

confidence: 99%

Full‐Field Analyses of Density‐Graded Elastomeric Foams Under Quasistatic and Impact Loadings

Smeets,

Kauvaka,

Uddin

et al. 2023

Adv Eng Mater

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“…That is, the initial negative Poisson's ratios tend to vary substantially during large deformation loading events, often starting at a negative value and approaching zero or even positive (non-auxetic) values at larger strains. Evidence for such strongly strain-dependent auxetic response has been reported for elastomeric foams and additively manufactured cellular structures [10][11][12][13], noting that an uncontrollable Poisson effect can adversely affect the performance and the sought application of the auxetic structures.…”

Section: Introductionmentioning

confidence: 97%

Modulating poisson’s ratio in flexible honeycombs by density and architecture gradations

Uddin,

Anni,

Youssef

et al. 2023

Eng. Res. Express

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Zero Poisson’s ratio structures are a new class of mechanical metamaterials wherein the absence of lateral deformations allows the structure to adapt and conform their geometries to desired shapes with minimal interventions. These structures have gained attention in large deformation applications where shape control is a key performance attribute, with examples including but not limited to shape morphing, soft robotics, and flexible electronics. The present study introduces an experimentally driven approach that leads to the design and development of (near) zero Poisson’s ratio structures with considerable load-bearing capacities through concurrent density and architecture gradations in hybrid honeycombs created from hexagonal and re-entrant cells. The strain-dependent Poisson’s ratios in hexagonal and re-entrant honeycombs with various cell wall thicknesses have been characterized experimentally. A mathematical approach is then proposed and utilized to create hybrid structures wherein the spatial distribution of different cell shapes and densities leads to the development of honeycombs with minimal lateral deformations under compressive strains as high as 0.7. Although not considered design criteria, the load-bearing and energy absorption capacities of the hybrid structures are shown to be comparable with those of uniform cell counterparts. Finally, the new hybrid structures indicate lesser degrees of instability (in the form of cell buckling and collapse) due to the self-constraining effects imposed internally by the adjacent cell rows in the structures.

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Density‐Dependent Impact Resilience and Auxeticity of Elastomeric Polyurea Foams

Cited by 2 publications

References 0 publications

Full‐Field Analyses of Density‐Graded Elastomeric Foams Under Quasistatic and Impact Loadings

Full‐Field Analyses of Density‐Graded Elastomeric Foams Under Quasistatic and Impact Loadings

Modulating poisson’s ratio in flexible honeycombs by density and architecture gradations

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