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Wyszukujesz frazę "Grima, J. N." wg kryterium: Autor

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    Wyświetlanie 1-4 z 4
    Tytuł:
    Modelling of the static and dynamic properties of tho-type silicates
    Autorzy:
    Cauchi, R.
    Grima, J. N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1954447.pdf
    Data publikacji:
    2014
    Wydawca:
    Politechnika Gdańska
    Tematy:
    auxetics
    zeolites
    thomsonite
    molecular dynamics
    Opis:
    Auxetic materials are materials exhibiting a negative Poisson’s ratio in one of their planes. This phenomenon has been studied in various materials. Zeolites are crystalline substances whose structure is characterised by the framework of linked tetrahedra, each consisting of four oxygen atoms surrounding a cation. The resulting interstitial spaces make them efficient for use as adsorbents and molecular sieves, and many studies have been focused on this aspect. Some of these zeolites may exhibit auxeticity at least in one of their planes. THO (and similar systems, such as NAT and EDI) together with the all-silica equivalent of these have been studied extensively via static simulations for their negative Poisson’s ratio in the (001) plane. In this paper a study of the all-silica equivalent of THO has been carried out via both static and dynamic simulations using the same force-field, where the system was subjected to stress along the x direction. The hypothesised semi-rigid mechanism of deformation, proposed by Grima et al. was then projected over this framework. The results obtained confirmed auxeticity along this plane by means of the COMPASS force-field, in both static and dynamic studies and compared well with the proposed mechanism of semi-rigid rotating polygons. It also showed that as the Young’s modulus of this mechanism increases other mechanisms of deformation increase in importance.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2014, 18, 1; 5-65
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Core-shell modelling of auxetic inorganic materials
    Autorzy:
    Zammit, V.
    Gatt, R.
    Attard, D.
    Grima, J. N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1954436.pdf
    Data publikacji:
    2014
    Wydawca:
    Politechnika Gdańska
    Tematy:
    Auxetic
    Zeolites
    negative Poisson's ratio
    mechanical properties
    materiały auksetyczne
    zeolity
    ujemny współczynnik Poissona
    właściwości mechaniczne
    Opis:
    This paper investigates the suitability of the General Utility Lattice Program (GULP) for studying auxetic materials at the molecular level. GULP is a force-field based molecular modelling package which incorporates the ‘core-shell’ model for simulating polarisability. A validation procedure was performed where the capability of GULP to reproduce the structural and mechanical properties of SOD (a zeolite for which the single crystalline elastic constants have been experimentally measured). It was found that not all GULP libraries (force-fields) could reproduce these properties, although the ‘Catlow 1992’ and ‘Sauer 1997’ libraries were found the produce good results. These libraries were then used to study the all-silica forms of various ‘presumably auxetic’ zeolites. The simulations generally confirmed the conclusions reported in earlier studies, and in particular, the fibrous zeolites THO, NAT and EDI where once again shown to be auxetic in the (001) plane. A study was also performed aimed at assessing the effect of interstitial species on the mechanical properties of NAT where it was shown that these species reduce the auxetic effect. This is very significant as once again we have confirmed the potential of these materials as molecular level auxetics, and hopefully, these results will result in generating more interest into the fascinating materials which could be used in many practical applications (e.g. tuneable molecular sieves).
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2014, 18, 2; 137--165
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Mechanical properties of 2D flexyne and reflexyne polyphenylacetylene networks: a comparative computer studies with various force-fields
    Autorzy:
    Trapani, L.
    Gatt, R.
    Mizzi, L.
    Grima, J. N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1938614.pdf
    Data publikacji:
    2015
    Wydawca:
    Politechnika Gdańska
    Tematy:
    2D flexyne polyphenylacetylene networks
    2D reflexyne polyphenylacetylene networks
    auxetics
    molecular simulations
    Opis:
    Auxetic materials exhibit the very unusual property of becoming wider when stretched and narrower when compressed, – they have a negative Poisson’s ratio. This unusual behaviour is the source of many desired effects in the materials’ properties and it is therefore, no wonder that auxetics are described as being superior to conventional materials in many practical applications. Here we make use of force-field based molecular modelling simulations in order to investigate the mechanical properties of polypehyleacetylene systems known as (n, m)-flexyne and (n, m)-reflexyne in an attempt to extend the existing knowledge there is regarding these systems. These systems have already attracted considerable consideration since negative on-axis Poisson’s ratios have been discovered for the reflexynes. We first developed a methodology for the modelling and property determination of flexyne and reflexyne network systems which we validated against existing published data. Then, extended the study to prove the simulated results were independent of the modelling methodology or the force-field used. In particular, we showed that on-axis auxeticity in the reflexynes is a force-field independent property, i.e. a property which is not an artefact of the simulations but a property which is likely to be present in the real materials if these were to be synthesised. We also studied and reported the shear behaviour of these systems were we show that the flexynes and reflexynes have very low shear moduli, a property which regrettably limits the prospects of these systems in many practical applications. Finally we examine the in-plane off-axis mechanical properties of the systems and we report that in general, these mechanical properties are highly dependent on the direction of loading. We also find that the auxeticity exhibited by the reflexynes on-axis is lost when these systems are loaded off axis since the Poisson’s ratios becomes positive very rapidly as the structure is stretched slightly off-axis (e.g. 15deg off-axis). This is once again of great practical significance as it highlights another major limitation of these systems in their use as auxetics.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2015, 19, 3; 237-296
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Simulations of the properties of elongated hexagonal dodecahedron systems
    Autorzy:
    Grima, J. N.
    Caruana-Gauci, R.
    Attard, D.
    Gatt, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/1954439.pdf
    Data publikacji:
    2022-02-01
    Wydawca:
    Politechnika Gdańska
    Tematy:
    auxetic
    empirical model
    negative Poisson's ratio
    negative compressibility
    cellular structure
    foams
    model empiryczny
    ujemny współczynnik Poissona
    negatywne ściśliwości
    struktura komórkowa
    pianki
    Opis:
    This study considers a 3D basic unit-cell proposed for auxetic and non-au xetic foams namely the elongated hexagonal dodecahedron deforming through changes in angle b etween its ligaments (idealised hinging model). This structure was studied in detail for the potential of exhibiting negative Poisson’s ratio and/or negative compressibility b y means of a method based on standard force-field molecular modelling technique, termed as Empiri cal 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, CaruanaGauci 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 ex hibit zero Poisson’s ratios in one of its planes and positive or negative Poisson’s ratios in other plan es, depending on the geometry of the model. It was also shown that under certain conditions, ne gative linear and/or area compressibility was also exhibited.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2014, 18, 2; 117--135
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-4 z 4

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