Flexible planar metamaterials with tunable Poisson’s ratios

Pagliocca, Nicholas; Uddin, Kazi Zahir; Anni, Ibnaj Anamika; Shen, Chen; Youssef, George; Koohbor, Behrad

doi:10.1016/j.matdes.2022.110446

Cited by 28 publications

(30 citation statements)

References 87 publications

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“…Perforated structures were gripped by two tapered aluminum gripping tabs on each end. [17] Global and local strain fields developed in the samples during mechanical tests were measured using a dual-camera DIC system. For mesoscale (local) strain measurements, a single rotating square near the center of the structure was considered.…”

Section: Mechanical Testing and Digital Image Correlationmentioning

confidence: 99%

“…[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. Results and Discussion…”

Section: Mechanical Testing and Digital Image Correlationmentioning

confidence: 99%

“…[ 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 oriented cuts. [ 45,46 ] For example, Shan et al [ 39 ] reported a case where perforated auxetic sheets can be designed with an isotropic response.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, spatial variation of cell density distribution has also been explored as a strategy to achieve global net-zero Poisson's ratios over extended strain ranges. [17,[47][48][49][50] In each of the aforementioned works, the perforation geometry is shown to control the macroscale response of the structure for a prescribed loading case. Considering the macroscale response, the existing auxetic geometric topologies can be recategorized into fewer classes due to their overlapping similarities in deformation patterns.…”

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confidence: 99%

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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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Section: Mechanical Testing and Digital Image Correlationmentioning

confidence: 99%

Section: Mechanical Testing and Digital Image Correlationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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

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“…Recent advancements in flexible polymeric foams suggest tunable mechanical performances comparable to those of agile additively manufactured structures by controlling the architecture, geometry, and density. − For example, the spatial variations of cell structure and density in functionally graded foam materials (FGFMs) make it possible to achieve higher strength and failure strains while simultaneously maintaining higher energy absorption properties at a lower overall structural weight. − …”

Section: Introductionmentioning

confidence: 99%

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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Modular Soft Robotic Actuators from Flexible Perforated Sheets

2023

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Soft robotic actuators can be designed to achieve complex and tailored motions while simultaneously leveraging their compliance to interact with complex and often delicate environments. Mechanical metamaterials reveal a route to customizable deformations, force exertion, and mechanical energy efficiency attainable by careful arrangement of local geometric features. Herein, modular soft robotic actuators are developed from soft elastomers and flexible thermoplastic sheets of various unit cell designs. The efforts are focused on center‐symmetric perforated sheets, which are formed into flexible cylindrical skins that surround the soft inflatable actuators. The results demonstrate the influence of perforation geometry on the spatial stiffness of the reinforcement structure and the proposed actuators’ response through several investigations. It is demonstrated that the free‐boundary displacement, maximal force exertion, and mechanical energy efficiency of extensile actuators are dependent on a change of deformation mode in the mesostructure. The spatial stiffness concept is extended to develop soft robotic actuators that can bend, twist, and perform hybrid motions, such as simultaneous bending and twisting. Multisegment soft robotic arms are also developed from the aforementioned actuators. Investigations in this study provide a step toward the development of highly customizable and programmable soft robotic actuators for various applications.

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Flexible planar metamaterials with tunable Poisson’s ratios

Cited by 28 publications

References 87 publications

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

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

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

Modular Soft Robotic Actuators from Flexible Perforated Sheets

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