Flexoelectric materials in micromechanics

Κνισοβίτης, Χρήστος; Knisovitis, Chris

dc.contributor.author	Κνισοβίτης, Χρήστος	el
dc.contributor.author	Knisovitis, Chris	en
dc.date.accessioned	2021-07-12T08:09:48Z
dc.date.available	2021-07-12T08:09:48Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/53605
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.21303
dc.rights	Default License
dc.subject	Φλεξοηλεκτρισμός	el
dc.subject	Αντιεπίπεδο πρόβλημα φλεξοηλεκτρισμού	el
dc.subject	Υπερβολικό αντιεπίπεδο πρόβλημα	el
dc.subject	Ρωγμή τύπου 3	el
dc.subject	Πεπερασμένα στοιχεία - Ανάλογη Εξίσωση	el
dc.subject	Flexoelectricity	en
dc.subject	Dynamic anti-plane flexoelectric problem	en
dc.subject	Hyperbolic problem	en
dc.subject	Crack mode III	en
dc.subject	FEM – Analogue Equation Method	en
dc.title	Flexoelectric materials in micromechanics	en
dc.title	Φλεξοηλεκτρικά Υλικά στην Μικρομηχανική	el
heal.type	masterThesis
heal.classification	Μικρομηχανική	el
heal.classification	Micromechanics	en
heal.language	en
heal.access	free
heal.recordProvider	ntua	el
heal.publicationDate	2021-06-29
heal.abstract	Flexoelectricity is the phenomenon that allows some materials to convert mechanical strain gradients to electrical polarizations and vice versa. As flexoelectricity is a ferroelectric phenomenon, its applications are of maximum importance and should be studied thoroughly. The polarization magnitude is connected to the strain gradients and so situations that produce large strain gradients are interesting. The cracking seems to be very promising. The mode III crack is an anti-plane problem that can be solved also considering the flexoelectric effect. As known from classic elasticity, the anti-plane problem is a sub-case of 3D-elasticity. The mode III crack, is also a dynamic problem. By considering the contribution of the flexoelectric phenomenon to the total energy density, a solution of the anti-plane flexoelectric problem can be formed. A direct analogue is presented between the anti-plane flexoelectric problem and the anti-plane couple stress elasticity problem, which allows the distinction of the flexoelectric problem into three regions: the elliptic, the hyperbolic and the intermediate. The hyperbolic region is studied further. The characteristic lines, a method of solving hyperbolic equations, allows some simplifications of the differential equation and thus a full field analytical solution is presented. Mach cones are visible as the displacement is concerned. For this displacement, the polarization can be calculated. The crack tip and the end of the cohesive zone are the positions of maximum polarization and thus positions of possible electrical yielding (abrupt change of the polarization vector). Also, the polarization of a screw-like dislocation is calculated. In this case, the polarization is described with a “δ function” – like distribution. The anti-plane dynamic problem is responsible for the propagation of waves. Because of the microstructure (for the couple stress elasticity problem, or the flexoelectric properties on the normal anti-plane problem), those waves are dispersive, a fact that signifies the possibilities of a lot more applications. The dispersion is the next thing studied. The dispersion relations show great similarity with viscoelastic materials, as the flexoelectric metamaterials are concerned. Lastly, through another analogue between the anti-plane problems and the plate problems, numerical calculations are possible for a great number of cases. The analogue is modified in order to be able to solve also hyperbolic problems. This is the first time the Analogue Equation Method is used in a Finite Element Code. Through a standard Finite Element Method (FEM) code (ABAQUS), the Mach cone - like displacement is proved, in the hyperbolic problem. Also, the angle of the cones, is in agreement with the previous bibliographic suggestions and depends on the microstructure and the velocity of the problem.	en
heal.advisorName	Γιαννακόπουλος, Αντώνιος	el
heal.committeeMemberName	Γιαννακόπουλος, Αντώνιος	el
heal.committeeMemberName	Κουμούσης, Βλάσης	el
heal.committeeMemberName	Ζήσης, Αθανάσιος	el
heal.academicPublisherID	ntua
heal.numberOfPages	200 σ.	el
heal.fullTextAvailability	false