OAR@UM Collection:
https://www.um.edu.mt/library/oar/handle/123456789/18430
2024-03-29T13:11:53ZThe multidirectional auxeticity and negative linear compressibility of a 3D mechanical metamaterial
https://www.um.edu.mt/library/oar/handle/123456789/105182
Title: The multidirectional auxeticity and negative linear compressibility of a 3D mechanical metamaterial
Authors: Dudek, Krzysztof K.; Attard, Daphne; Gatt, Ruben; Grima Delia Spiteri Cornish, James N.; Grima, Joseph N.
Abstract: In this work, through the use of a theoretical model, we analyse the potential of a specific
three-dimensional mechanical metamaterial composed of arrowhead-like structural units to exhibit
a negative Poisson’s ratio for an arbitrary loading direction. Said analysis allows us to assess its
suitability for use in applications where materials must be able to respond in a desired manner to
a stimulus applied in multiple directions. As a result of our studies, we show that the analysed system
is capable of exhibiting auxetic behaviour for a broad range of loading directions, with isotropic
behaviour being shown in some planes. In addition to that, we show that there are also certain
loading directions in which the system manifests negative linear compressibility. This enhances its
versatility and suitability for a number of applications where materials exhibiting auxetic behaviour
or negative linear compressibility are normally implemented.2020-01-01T00:00:00ZUnusual thermoelastic properties of methanol monohydrate
https://www.um.edu.mt/library/oar/handle/123456789/105177
Title: Unusual thermoelastic properties of methanol monohydrate
Authors: Grima, Joseph N.; Attard, Daphne; Gatt, Ruben
Abstract: Wen a material is heated, we expect
it to expand, and when squeezed
on all sides by hydrostatic pressure,
we expect it to shrink, but materials
or structures can respond in unexpected
ways. Some may exhibit negative thermal
expansion (NTE)—shrinking when heated
(1–8)—or negative compressibility (NC)
(8–13)—expanding when subjected to a
positive hydrostatic pressure—and some
may exhibit both properties. [Excerpt]2011-01-01T00:00:00ZSimulations of the properties of elongated hexagonal dodecahedron systems
https://www.um.edu.mt/library/oar/handle/123456789/105170
Title: Simulations of the properties of elongated hexagonal dodecahedron systems
Authors: Grima, Joseph N.; Caruana-Gauci, Roberto; Attard, Daphne; Gatt, Ruben
Abstract: This study considers a 3D basic unit-cell proposed for auxetic and non-auxetic foams namely the elongated hexagonal dodecahedron deforming through changes in angle between its ligaments (idealised hinging model). This structure was studied in detail for the potential of exhibiting negative Poisson’s ratio and/or negative compressibility by means of a method based on standard force-field molecular modelling technique, termed as Empirical Modelling Using Dummy Atoms (EMUDA). The mechanical properties obtained from this method were then compared to a previously published analytical model of this structure [Grima J N, Caruana-Gauci R, Attard D, and Gatt R 2012, Proc. Roy. Soc. A 468 3121], and found to be in good agreement with each other. The results showed that this system can exhibit zero Poisson’s ratios in one of its planes and positive or negative Poisson’s ratios in other planes, depending on the geometry of the model. It was also shown that under certain conditions, negative linear and/or area compressibility was also exhibited.2014-01-01T00:00:00ZThe auxetic behavior of a general Star-4 structure
https://www.um.edu.mt/library/oar/handle/123456789/105164
Title: The auxetic behavior of a general Star-4 structure
Authors: Farrugia, Pierre-Sandre; Gatt, Ruben; Attard, Daphne; Attenborough, Frances Ruth; Evans, Ken E.; Grima, Joseph N.
Abstract: An analytical model for a general Star-4 system, having different ligament lengths, angles, and ligament thickness, is derived using Castigliano's second theorem. The analytical model is validated through finite element analysis and experimental work. The results obtained show that, depending on the parameters used, the general Star-4 system can show a wide range of Poisson's ratios with the potential of obtaining giant negative Poisson's ratios (in the order of −8) for certain conformations. The wide range of Poisson's ratio is explained in terms of the different geometrical conformations obtainable by the system, where the star-ligaments can also describe rhombi, irregular octagons, rectangles, and accordion-like systems, together with changes in the deformation mechanism due to variations in parameters. For example, if one set of star-ligaments is much thicker than the other, the deformation of the star would be akin to that of the hexagonal reentrant unit cell.2021-01-01T00:00:00Z