Dynamic Behavior and Impact Tolerance of Elastomeric Foams Subjected to Multiple Impact Conditions

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

doi:10.1007/s40870-022-00340-z

Cited by 9 publications

(13 citation statements)

References 32 publications

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“…A possible avenue for the study of mechanical and energy dissipation behaviors after repeated loading is the estimation of apparent stiffness variations as a function of the adhesive properties. Mesomechanics characterizations similar to those reported by Koohbor et al 42 can be performed for this purpose.…”

Section: Resultsmentioning

confidence: 84%

“…The slower onset of densification in the dynamic regime is rooted in the rapid cell collapse, quickly engaging the cell-wall-entrapped base material in the overall response demonstrated by the significant increase in the stress in the densification region. Notably, polyurea is a shock-tolerant and impact-resistant material; 40 − 42 hence, the significant rise in the stress as the foam stack densifies is associated with a negligible permanent set, as recently shown in a recent article. 31 …”

Section: Resultsmentioning

confidence: 86%

“…Therefore, the reduction in the stiffness difference in impact loading leads to less intense property gradients across the interlayer, practically attributed to a lower likelihood of damage initiation from the interface. While beyond the scope of the present study, concepts involving the role of adhesive interlayer properties on the damage initiation and evolution in graded foams subjected to repeated impact conditions , would be an interesting topic for future research. In such cases, an optimal interface layer may be identified by taking into account the interplay between mechanical and energy dissipation behaviors as well as the long-term use of foam stacks, especially considering repeated low-rate loading (e.g., for use in a walking shoe midsole) or higher energy impact conditions (e.g., for use as helmet liners).…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2022

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The concept of density-graded foams has been proposed to simultaneously enhance strain energy dissipation and the load-bearing capacities at a reduced structural weight. From a practical perspective, the fabrication of density-graded foams is often achieved by stacking different foam densities. Under such conditions, the adhesive interlayer significantly affects the mechanical performance and failure modes of the structure. This work investigates the role of different adhesive layers on the mechanical and energy absorption behaviors of graded flexible foams with distinct density layers. Three adhesive candidates with different chemical, physical, and mechanical characteristics are used to assemble density-graded polyurea foam structures. The mechanical load-bearing and energy absorption performances of the structures are evaluated under quasi-static and dynamic loading conditions. Mechanical tests are accompanied by digital image correlation (DIC) analyses to study the local strain fields developed in the vicinity of the interface. Experimental measurements are also supplemented by model predictions that reveal the interplay between the mechanical properties of an adhesive interlayer and the macroscale mechanical performance of the graded foam structures. The results obtained herein demonstrate that the deformation patterns and macroscale properties of graded foam composites can be tuned by selecting different bonding agents. It is also shown that the proper selection of an adhesive can be a practical way to address the strength–energy dissipation dichotomy in graded structures.

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Section: Resultsmentioning

confidence: 84%

Section: Resultsmentioning

confidence: 86%

Section: Resultsmentioning

confidence: 99%

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

et al. 2022

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“…[65] The incremental definition of Poisson's ratio (i.e., ν ¼ Àdε t /dε l ) was used as it is documented to provide a more reliable metric for the characterization of auxetic behavior in hyperelastic materials. [66][67][68] All strain field data were smoothed with an exponential smoothing function with a damping factor of 0.3 due to the intrinsic noise associated with numerical differentiation associated with the incremental Poisson's ratio. Further details regarding strain measurement protocols are excluded for brevity but can be found in Pagliocca et al [17] 3.…”

Section: Mechanical Testing and Digital Image Correlationmentioning

confidence: 99%

Multiscale Strain Field Characterization in Flexible Planar Auxetic Metamaterials with Rotating Squares

et al. 2022

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Auxetic materials exhibit a negative Poisson's ratio when subjected to mechanical load. [1][2][3][4][5] For example, auxetic structures expand longitudinally and laterally when subjected to uniaxial tension instead of experiencing lateral contraction commonly seen in their conventional counterparts. Researchers have broadly considered the use of such materials and structures in many applications, including but not limited to biomechanics, flexible electronics, and soft robotics. [6][7][8][9] The growing interest in using auxetic structures in these applications is due to their improved mechanical properties, such as higher indentation resistance, improved vibration damping, resistance to shear, and enhanced fracture toughness, compared with their nonauxetic counterparts. [10][11][12][13] Auxetic structures are generally classified as a subset of "mechanical metamaterials" as their novel properties are not commonly found in nature or other conventional engineering materials. [3,14,15] The so-called mechanical metamaterials are highly influenced by the augmentation of their local morphology. Therefore, their physical properties can be controlled by certain microstructural and geometric features, thus allowing broader control of the behavior by design rather than the chemical composition of their constituent materials. [16,17] Property-adjustable auxetic materials with variable responses in changing environments have also been developed for various applications. [18][19][20][21][22][23] For instance, embedding magnetic insertions in auxetic metamaterials is shown to change the cellular configuration upon the application of a magnetic field, switching nonauxetic to an auxetic response. [24] Similar behaviors have been observed when a quadrilateral cellular structure consisting of bimaterial strips converts into a convex or concave shape with thermal triggers. [25] Researchers have explored various cell topologies that lead to auxetic behavior. [3,5,[26][27][28][29] The pioneering experimental studies in this field are credited to Lakes, who investigated auxetic foams. [30] In recent years and in line with the advancements in additive manufacturing, practical and cost-effective pathways to the realization of these architected structures have become more easily achievable. [31][32][33][34][35][36][37] Specifically, the fabrication of planar mechanical metamaterials with tunable properties has attracted great attention. For example, the cut and slit design strategy, wherein perforations are intentionally introduced into a sheet to promote auxeticity, has been explored in several studies. [35,38,39] These perforation patterns used to achieve auxetic behaviors include kagome lattices, [39] diamonds, [40] circles, [41] triangles, [42] ellipses, [43] stars, [31] self-similar squares, [44] and rectangles. [17,35,36] The auxetic response has also been achieved through randomly

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“…From a mechanics perspective, the hyper-viscoelastic properties of bulk polyurea are also embodied in the foamed version, , resulting in sustaining single and repeated impacts at different energies. ,, Polyurea foams investigated herein have been classified as self-reinforced, semiclosed cellular solids based on a twofold rationale. First, polyurea microspheres nucleate during the violent mixing step to froth the chemical constituents in the water mixing solution based on the precipitation polymerization approach. ,, The emulsified polyurea microspheres are then deposited on the internal surfaces of the cells during the water-draining step, effectively reinforcing the cells without unnecessarily increasing the wall thickness, i.e., without substantially increasing the density .…”

Section: Introductionmentioning

confidence: 99%

Quasi-Static Mechanical Response of Density-Graded Polyurea Elastomeric Foams

Smeets

Koohbor

Youssef

2023

ACS Appl. Polym. Mater.

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Density gradation of foam structures has been investigated and found to be a practical approach to improve the mechanical efficacy of protective padding in several applications based on nature-based evidence of effectiveness. This research aims to disclose a discrete gradation approach without adhesives by relying on the properties of the frothed foam slurry to bond and penetrate through previously cured foam sheets naturally. As confirmed by electron microscopy observations, bilayer-and trilayergraded elastomeric polyurea foam sheets were fabricated, resulting in seamless interfaces. The mechanical performance of seamless, graded foam samples was compared with monolayer, mono-density benchmark foam, considered the industry standard for impact mitigation. All foam samples were submitted to compressive loading at a quasi-static rate, reporting key performance indicators (KPIs) such as specific energy absorption, efficiency, and ideality. Polyurea foams, irrespective of gradation and interface type, outperformed benchmark foam in several KPIs despite the drastic difference in the effective or average density. The average compressive stress−strain curves were fitted into empirical constitutive models to reveal critical insights into the elastic, plateau, and densification behaviors of the tested foam configuration. The novelty of these outcomes includes (1) a fabrication approach to adhesive-free density-graded foam structures, (2) implementation of a diverse set of KPIs to assess the mechanical efficacy of foams, and (3) elucidation of the superiority of polyurea foam-based lightweight protective paddings. Future research will focus on assessing the dynamic performance of these graded foam structures under impact loading conditions at a wide range of velocities.

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Dynamic Behavior and Impact Tolerance of Elastomeric Foams Subjected to Multiple Impact Conditions

Cited by 9 publications

References 32 publications

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

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

Multiscale Strain Field Characterization in Flexible Planar Auxetic Metamaterials with Rotating Squares

Quasi-Static Mechanical Response of Density-Graded Polyurea Elastomeric Foams

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