Experimental and computation assessment of thermomechanical effects during auxetic foam fabrication

Critchley, Richard; Smy, Victoria; Corni, Ilaria; Wharton, J.A.; Walsh, Frank C.; Wood, R.J.K.; Stokes, K.R.

doi:10.1038/s41598-020-75298-w

Cited by 16 publications

(8 citation statements)

References 53 publications

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“…Open cell polyurethane foams with two different cell structures were thermo-mechanically fabricated from 32 (z-axis) by 32 (x-axis) by 96 (y-axis) mm samples (PUR30FR, Custom Foams, as used in [35,55,75]). Fabrication conditions and, hence, imparted cell structures were selected based on previous work to give high magnitude NPR in all three orthogonal axes [58,67,76] or just one axis [55,57,62,77]. For the uniform triaxial conversions, compression to 40% engineering strain was imposed with aluminium moulds to modify cell shape in each axis (Figure 1a), giving a volumetric compression ratio (final/original volume) of five.…”

Section: Fabrication: Open Cell Foamsmentioning

confidence: 99%

“…During such impact tests, a drop mass is decelerated by the energy absorbing material within the product, imparting variable strain rates up to and above 200 s −1 that reduce to 0 s −1 at maximum compression. Despite the wealth of research into auxetic open cell foam, most of the previous work measured Poisson's ratio and Young's modulus quasi-statically (<1 s −1 , [34,54,60,[67][68][69][70]), or at intermediate (<10 s −1 , [52]) strain rates. Poisson's ratios of auxetic open cell foams, between 0 and −0.1, have been measured using marker tracking during impact tests at higher, but variable, strain rates of ~100 s −1 [36,37].…”

Section: Introductionmentioning

confidence: 99%

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Effect of Compressive Strain Rate on Auxetic Foam

et al. 2021

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Auxetic foams have previously been shown to have benefits including higher indentation resistance than their conventional counterparts, due to their negative Poisson’s ratio, making them better at resisting penetration by concentrated loads. The Poisson’s ratio and Young’s modulus of auxetic open cell foams have rarely been measured at the high compressive strain rates typical during impacts of energy absorbing material in sporting protective equipment. Auxetic closed cell foams are less common than their open cell counterparts, and only their quasi-static characteristics have been previously reported. It is, therefore, unclear how the Poisson’s ratio of auxetic foam, and associated benefits such as increased indentation resistance shown at low strain rates, would transfer to the high strain rates expected under impact. The aim of this study was to measure the effect of strain rate on the stiffness and Poisson’s ratio of auxetic and conventional foam. Auxetic open cell and closed cell polymer foams were fabricated, then compression tested to ~80% strain at applied rates up to 200 s−1, with Poisson’s ratios obtained from optical full-field strain mapping. Open cell foam quasi-static Poisson’s ratios ranged from −2.0 to 0.4, with a narrower range of −0.1 to 0.3 for closed cell foam. Poisson’s ratios of auxetic foams approximately halved in magnitude between the minimum and maximum strain rates. Open cell foam quasi-static Young’s moduli were between 0.02 and 0.09 MPa, whereas closed cell foams Young’s moduli were ~1 MPa, which is like foam in protective equipment. The Young’s moduli of the auxetic foams approximately doubled at the highest applied strain rate of 200 s−1.

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Section: Fabrication: Open Cell Foamsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of Compressive Strain Rate on Auxetic Foam

et al. 2021

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“…From a synthesis point of view, the alveolar polyurethane foams are the products of a chemical reaction of a polyisocyanate, polyol, and a blowing agent. 21 This class of polymers can lead to flexible foams, rigid or semirigid, according to the composition and chemical structure of the used reagents. 22 The expected filled polyurethane foam within open cells will be physiochemically characterized and evaluated under dynamic tests.…”

Section: Methodsmentioning

confidence: 99%

Preparation of Nonlethal Projectiles by Polyurethane Foam with the Dynamic and Microscopic Characterization for Risk Assessment and Management

2022

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Nonlethal projectiles are manufactured and designed proportionately, with a minimal likelihood of mortality or harm. However, numerous real-world examples indicate that nonlethal projectiles can potentially inflict severe lesions and death in some circumstances. As a result, it is essential to design and manage the manufacture of projectile materials to achieve maximum efficacy with the least amount of collateral damage. The current paper provides a technique for generating and analyzing filled polyurethane (PU) foams and studying their viscoelastic characteristics. The sand and graphite composition ranged between 5 and 10% by weight. The suggested technique seeks to exert control over the evolution of the microstructure. The mechanical characteristics were obtained by dynamic mechanical analysis (DMA) testing. We made a pneumatic launcher and a sturdy rigid wall. In addition, the artificial human head is covered with force sensors to perform dynamic characterization. Also, scanning electron microscopy (SEM) of the polyurethane foam cross sections demonstrated that the average cell size of 98 μm was unaffected by the fillings’ content. Furthermore, X-ray diffraction analysis (XRD) characterized the developmental foams’ physicochemical properties. Finally, we assessed the dynamic search for nonlethal projectiles. We recorded the viscous criteria (VC max ) values to check for nonlethal projectiles.

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“…The final conclusions of the DoE showed that the VCR is the most statistically important manufacturing, while no significant statistical correlation could be identified with the temperature, heating times provided and the cooling methodologies. Critchley et al [70] recently provided an updated statistical approach for the optimization of the manufacturing parameters to improve the efficiency of the production. An optimal combination of VCR, porosity and heating time was recommended for a conversion temperature of 200 °C, detailed parameters are also shown in Figure . 10.…”

Section: Parametric Manufacturingmentioning

confidence: 99%