Shape memory behaviour in auxetic foams: Mechanical properties

Bianchi, Matteo; Scarpa, Fabrizio; Smith, Christopher W.

doi:10.1016/j.actamat.2009.09.063

Cited by 118 publications

(131 citation statements)

References 36 publications

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“…The cell is also defined by a global internal cell angle θ and another angle related to the kink Kinks and cross-section reduction are produced during the mechanical compression phase within the mould (as also partially observed in 22 ), and this would result in a reduction in the restorative force acting to reset the foam to its original dimensions. This would prevent complete shape recovery and would allow relatively facile compressive deformation to a processinduced intrinsic auxetic structure after the first several cycles.…”

Section: (A) (B) (C) (D) (E)mentioning

confidence: 99%

“…A shape memory effect can be also induced in negative Poisson's ratio foam specimens by applying a specific temperature profile, causing the dimensions of the NPR foam to return to their original values (conversion to returned phase). The process of converting PU foam from conventional to NPR (also denominated as auxetic 21 ), and the subsequent reconversion to the returned (or original) phase, is designated as one conversion cycle 22 . Bianchi et al 22 suffer an important drawback due to their shape memory effect, due to which they revert back to their original structure (having a positive Poisson's ratio) when exposed to heat or solvents.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: (A) (B) (C) (D) (E)mentioning

confidence: 99%

Section: Introductionmentioning

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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“…In this sense, auxetic materials can be applied to improve protective materials or energy-absorbing materials [14]. Furthermore, they can also be applied as an efficient membrane filter with variable permeability [15,16], fasteners [17,18], shape memory materials [19] and acoustic dampeners [20,21]. They have the ability to form dome-shaped structures when bent [4,22], undergoing double (synclastic) curvature, as opposed to the saddle shape (anticlastic curvature) that non-auxetic materials adopt when subjected to out-of-plane bending moments.…”

Section: Introductionmentioning

confidence: 99%

Auxetic two-dimensional lattices with Poisson's ratio arbitrarily close to −1

Cabras

Brun

2014

Proc. R. Soc. A.

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In this paper, we propose a class of lattice structures with macroscopic Poisson's ratio arbitrarily close to the stability limit −1. We tested experimentally the effective Poisson's ratio of the microstructured medium; the uniaxial test was performed on a thermoplastic lattice produced with a threedimensional printing technology. A theoretical analysis of the effective properties was performed, and the expression of the macroscopic constitutive properties is given in full analytical form as a function of the constitutive properties of the elements of the lattice and on the geometry of the microstructure. The analysis was performed on three microgeometries leading to an isotropic behaviour for the cases of threeand sixfold symmetries and to a cubic behaviour for the case of fourfold symmetry.

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“…Applying compression and heating within windows of temperature and time (conversion windows) produces NPR samples. Heating below a temperature threshold (i.e., under-heating) produces unstable samples that return towards their original dimensions when released from the mould [26]. Over-heating samples can change the base polymer or cause adhesion of cell ribs, leading to a positive Poisson's ratio [27].…”

Section: Introductionmentioning

confidence: 99%

Controlling Density and Modulus in Auxetic Foam Fabrications—Implications for Impact and Indentation Testing

Duncan¹,

Allen²,

Foster³

et al. 2018

The 12th Conference of the International Sports Engineering Association

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Foams are commonly used for cushioning in protective sporting equipment. Volumetrically compressing open-cell polyurethane foam buckles cell ribs creating a re-entrant structure-set by heating then cooling-which can impart auxetic behaviour. Theoretically, auxetic materials improve impact protection by increasing indentation resistance and energy absorption, potentially reducing sporting injuries and burdens on individuals, health services and national economies. In previous work, auxetic foam exhibited ~3 to ~8 times lower peak force (compared to its conventional counterpart) under impacts adopted from tests used to certify protective sporting equipment. Increases to the foam's density and changes to stress/strain relationships (from fabrication) mean Poisson's ratio's contribution to reduced peak forces under impact is unclear. This work presents a simple fabrication method for foam samples with comparable density and linear stress/strain relationship, but different Poisson's ratios ranging between 0.1 and −0.3, an important step in assessing the Poisson's ratio's contribution to impact force attenuation.

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Shape memory behaviour in auxetic foams: Mechanical properties

Cited by 118 publications

References 36 publications

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

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

Auxetic two-dimensional lattices with Poisson's ratio arbitrarily close to −1

Controlling Density and Modulus in Auxetic Foam Fabrications—Implications for Impact and Indentation Testing

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