Project Number: KD04JNG, KD01JNG and KD02RGC
Auxetics are materials and systems which exhibit the very unusual properties of becoming wider when stretched and narrower when squashed, that is, they have Negative Poisson's Ratio.
A team of University researchers have extensive expertise on materials possessing auxetic properties and how they can be used to develop and manufacture new or improved commercial structures and products.
They have also developed a novel way of converting conventional foam to auxetic foam through the use of solvent instead of heat. The process which was developed can be divided into three steps:
Why opt for an auxetic material?
Apart from possessing a Negative Poisson's Ratio, auxetic materials display additional unique qualities such as increased shear stiffness, an increased plane strain fracture toughness and an increased indentation resistance. When an object hits an auxetic material and compresses it in one direction, the material contracts laterally. That is, material flows into the location of impact creating a denser material which is less resistant to impact.
Auxetic materials are also known to have better shock and vibration absorption properties. They also have a natural tendency to form dome-shaped double-curved surfaces, unlike conventional materials which tend to form saddle-shaped surfaces. Such materials are particularly desirable in applications that require highly curved hard surfaces, such as those found in the body parts of aircrafts and cars.
How can this be applied to foams?
Current methods of converting conventional foams to auxetic foams focus around compressing, heating and cooling the foam. This method can be time consuming and costly when considering the heating equipment required. The proposed production process is more energy efficient than current methods since it does not require heating. This, coupled with the fact that solvents may be reused several times lowers the production costs and also allows for a more environmentally friendly process. The use of solvents also removes the risk of the foam being degraded as part of the heating process. As solvents flow homogenously, the process for converting large samples of auxetic foam blocks would be more efficient than current processes.
Auxetic materials and structures can also be used to replace conventional components in various products used in specialised applications to produce higher quality products.
This technology surrounding auxetic foams may be used to produce a number of products, for which enhanced capabilities will emerge as a result of the superior properties that auxetic foams have over conventional foam. This can be applied to:
The foam has been prototyped.
Patent granted. A patent application number GB1107220.4 was submitted by the University of Malta in the United Kingdom in May 2011. This was granted under number GB2480905 B in July 2013. Patent application number MT4236 submitted in Malta was also granted to the University of Malta.
The team have extensive know how in the field of auxetics and how it can be applied to the development and manufacture new or improved commercial structures and products. We are interested in collaborating with entities to design smart materials around their technologies.
Prof. Joseph N Grima
Prof. Ruben Gatt
Dr Daphne Attard
K Boba K., Bianchi M., McCombe G., Gatt R., Griffin AC., Richardson RM., Scarpa F., Hamerton I., Grima JN. (2016). 'Blocked shape memory effect in negative Poisson’s ratio polymer metamaterials.' ACS Applied Materials & Interfaces 8 (31), 20319-20328,
Attard D., Degabriele EP., Grima JN. (2016). 'Nano networks exhibiting negative linear compressibility.' Physica Status Solidi (b) Vol 253, Issue 7 (1419-1427)
Attard D., Caruana-Gauci R., Gatt R., Grima JN. (2016). 'Negative linear compressibility from rotating rigid units.' Physica Status Solidi (b) Vol. 253, Issue 7 (1410 - 1418)
Grima JN., Mizzi L., Poźniak AA., Wojciechowski KW. (2016). 'Planar auxeticity from elliptic inclusions.' Elsevier: Composites Part B- Engineering.
Evans E.E., Grima JN.(2006) 'Auxetic behavior from rotating triangles'. Journal of Materials Science 41; 3193–3196
Dudek KK., Attard D., Caruana-Gauci R., Grima JN,. Wojciechowski KW. (2016) 'Unimode metamaterials exhibiting negative linear compressibility and negative thermal expansion.' IOP Publishing: Smart Materials and Structures Vol 25, Issue 2 (0205009)
Azzopardi KM., Gatt R., Grima JN, Mizzi L.(2016). 'Auxetic perforated mechanical metamaterials with randomly oriented cuts.' Advanced Materials Vol 28, Issue 2 (385-389)
Attard D., Gatt R., Grima JN., Mizzi L, Pozniak AA., Wojciechowski KW (2015). 'Influence of translational disorder on the mechanical properties of hexachiral honeycomb systems.' Elsevier: Composites Part B: Engineering Vol 80 (84-91)
Agius TP., Attard L., Azzopardi KM., Casha A., Chockalingam N., Formosa C., Gatt A., Gatt R., Grima JN., Schembri-Wismayer P., Vella Wood M, Zarb F. (2015). 'Negative Poisson’s ratios in tendons: an unexpected mechanical response.' Elsevier: Acta biomaterialia Vol 24 (201-208)
Caruana-Gauci R., Dudek KK., Dudek MR., Grima JN., Wojciechowski KW. (2015) 'Colossal magnetocaloric effect in magneto-auxetic systems'. IOP Publishing: Smart Materials and Structures Vol 24, Issue 8 (085027)
Attard D., Bajada M., Dudek KK., Gatt R., Grima JN., Scerri S. (2015). 'Maximizing negative thermal expansion via rigid unit modes: a geometry-based approach'. The Royal Society: Proc. R. Soc. A Vol 471 Issue 2179 (20150188).
Alderson A., Grima JN., Scarpa F., Wojciechowski KW. (2015). 'Auxetics and other systems of “negative” characteristics'. Physica Status Solidi (b) Vol 252, Issue 7 (1421-1425)
Gatt R., Grima JN., Mizzi L. (2015). 'Non‐porous grooved single‐material auxetics'. Physica Status Solidi (b) Volume 252, Issue 7 (1559-1564)
Cauchi R., Formosa JP., Grima JN. (2015). 'Carbon allotropes exhibiting negative linear compressibility'. Physica Status Solidi (b) Vol 252 Issue 7 (1656-1663)
Attard D., Azzopardi KM, Gatt R., Grima JN., Mizzi L. (2015). 'Auxetic metamaterials exhibiting giant negative Poisson's ratios'. Physica Status Solidi (RRL)-Rapid Research Letters Vol 9 Issue 7 (425-430)
Attard D., Azzopardi JI., Azzopardi KM., Briffa J., Casha A., Gatt R., Mizzi L., Grima JN. (2015). 'Hierarchical Auxetic Mechanical Metamaterials'. Nature Publishing Group: Scientific reports Vol 5 (8395)
Attard D., Cauchi R., Grech MC., Gatt R., Grima JN., Mizzi L., Rybicki J., Winczewski SN., Wojciechowski KW. (2015). 'Tailoring graphene to achieve negative poisson's ratio properties'. Advanced Materials Vol 27 Issue 8 (1455-1459)
Azzopardi KM., Brincat JP., Gatt R., Grima JN., Mizzi L. (2015). 'On the Effect of the Mode of Connection between the Node and the Ligaments in Anti‐Tetrachiral Systems'. Advanced Engineering Materials Vol 17 Issue 2 (189-198)
Gatt R., Grima R., Mizzi L., Trapani L. (2015). 'Mechanical Properties of 2D Flexyne and Reflexyne Polyphenylacetylene Networks: A Comparative Computer Studies with Various Force-Fields'. TASK Quarterly: scientific bulletin of Academic Computer Centre in Gdansk Vol 19 Issue 3 (237-296)
Azzopardi KM., Brincat JP., Gatt R., Grima JN. (2015). 'Anomalous elastic properties in stishovite'. RSC Advances Vol 5 Issue 12 (8974-8980)
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