Compressive uniaxial properties of auxetic open cell PU based foams

Cadamagnani, F.; Frontoni, S.; Bianchi, Matteo; Scarpa, Fabrizio

doi:10.1002/pssb.200982044

Cited by 14 publications

(11 citation statements)

References 29 publications

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“…We note that this stress-strain profile for the 3D printed s-hinged auxetic closely matches that of less well-defined open-cell polyurethane foams currently researched as isotropic auxetics, and could improve our understanding of their behavior, including the change to a quasi-exponential stress-strain curve (Cadamagnani et al, 2009). This deformation behavior can be tuned by changing the arc angle of the s-hinge, in a controllable manner similar to that shown for kagome lattices (Wu et al, 2015).…”

Section: Deformation Characterization Of S-hinge Structuresupporting

confidence: 64%

Low Fatigue Dynamic Auxetic Lattices With 3D Printable, Multistable, and Tuneable Unit Cells

et al. 2018

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Stress distribution has led to the design of both tough and lightweight materials. Truss structures distribute stress well and are commonly used to design lightweight materials for applications experiencing low strains. In 3D lattices, however, few structures allow high elastic compression and tunable deformation. This is especially true for auxetic material designs, such as the prototypical re-entrant honeycomb with sharp corners, which are particularly susceptible to stress concentrations. There is a pressing need for lightweight lattice designs that are dynamic, as well as resistant to fatigue. Truss designs based on hinged structures exist in nature and delocalize stress rather than concentrating it in small areas. They have inspired us to develop s-hinge shaped elastic unit cell elements from which new classes of architected modular 2D and 3D lattices can be printed or assembled. These lattices feature locally tunable Poisson ratios (auxetic), large elastic deformations without fatigue, as well as mechanical switching between multistable states. We demonstrate 3D printed structures with stress delocalization that enables macroscopic 30% cyclable elastic strains, far exceeding those intrinsic to the materials that constitute them (6%). We also present a simple semi-analytical model of the deformations which is able to predict the mechanical properties of the structures within <5% error of experimental measurements from a few parameters such as dimensions and material properties. Using this model, we discovered and experimentally verified a critical angle of the s-hinge enabling bistable transformations between auxetic and normal materials. The dynamic modeling tools developed here could be used for complex 3D designs from any 3D printable material (metals, ceramics, and polymers). Locally tunable deformation and much higher elastic strains than the parent material would enable the next generation of compact, foldable and expandable structures. Mixing unit cells with different hinge angles, we designed gradient Poisson's ratio materials, as well as ones with multiple stable states where elastic energy can be stored in latching structures, offering prospects for multi-functional designs. Much like the energy efficient Venus flytrap, such structures can store elastic energy and release it on demand when appropriate stimuli are present.

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Section: Deformation Characterization Of S-hinge Structuresupporting

confidence: 64%

Low Fatigue Dynamic Auxetic Lattices With 3D Printable, Multistable, and Tuneable Unit Cells

et al. 2018

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“…Since 1987, this production process has been applied by numerous investigations and a number of modifications have been reported . While each has been altered either to produce differences within the polymeric materials or to optimise the process the overall principle has remained the same, i.e .…”

Section: Methods To Convert Conventional Foams Into Auxeticmentioning

confidence: 99%

“…Although optimum compression ratio ranges have been suggested, it has to be remembered that the optimum permanent compression to achieve the best negative Poisson's ratio depends on the initial foam density and appears to have a purely geometrical origin, as the same negative Poisson's ratio value was observed for metallic and polymeric foams with the same relative density . The majority of R c values reported in the literature fell within this range ; however, experiments with greater volumetric compression ratios have also been reported but only with respect to mechanical testing and not volumetric effects .…”

Section: Parameters Affecting Manufacture Of Auxetic Foamsmentioning

confidence: 99%

A review of the manufacture, mechanical properties and potential applications of auxetic foams

Critchley

Corni

Wharton

et al. 2013

Physica Status Solidi (b)

187

116

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Auxetics are a modern class of material fabricated by altering the material microstructure. Unlike conventional materials, auxetics exhibit a negative Poisson's ratio when subjected to tensile loading. These materials have gained popularity within the research community because of their enhanced properties, such as density, stiffness, fracture toughness and dampening. This paper provides a critical oversight of the auxetic field with particular emphasis to the auxetic foams, due to their low price, easy availability and desirable mechanical properties. Key areas discussed include the fabrication method, the effects played by different parameters (temperature, heating time, cell shape and size and volumetric compression ratio), microstructural models, mechanical properties and potential applications.

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“…The specimens had initial dimensions of 30 mm diameter and 160 mm in length (Figure 1). The pristine foams have been converted into the NPR (or auxetic) phase using the classical manufacturing route described in 24,25 . The specimens have been compressed to their 50 % and 37% of the original dimensions along the axial (i.e.…”

Section: Manufacturing and Testingmentioning

confidence: 99%

Blocked Shape Memory Effect in Negative Poisson’s Ratio Polymer Metamaterials

Boba

Bianchi

McCombe

et al. 2016

ACS Appl. Mater. Interfaces

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We describe a new class of negative Poisson's ratio (NPR) open cell PU-PE foams produced by blocking the shape memory effect in the polymer. Contrary to classical NPR open cell thermoset and thermoplastic foams that return to their auxetic phase after reheating (and therefore limit their use in technological applications), this new class of cellular solids has a permanent negative Poisson's ratio behavior, generated through multiple shape memory (mSM) treatments that lead to a fixity of the topology of the cell foam. The mSM-NPR foams have Poisson's ratio values similar to the auxetic foams prior their return to the conventional phase, but compressive stress-strain curves similar to the ones of conventional foams. The results show that by manipulating the shape memory effect in polymer microstructures it is possible to obtain new classes of materials with unusual deformation mechanisms.2

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Compressive uniaxial properties of auxetic open cell PU based foams

Cited by 14 publications

References 29 publications

Low Fatigue Dynamic Auxetic Lattices With 3D Printable, Multistable, and Tuneable Unit Cells

Low Fatigue Dynamic Auxetic Lattices With 3D Printable, Multistable, and Tuneable Unit Cells

A review of the manufacture, mechanical properties and potential applications of auxetic foams

Blocked Shape Memory Effect in Negative Poisson’s Ratio Polymer Metamaterials

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