IMT Institutional Repository: No conditions. Results ordered -Date Deposited. 2019-10-14T18:35:31ZEPrintshttp://eprints.imtlucca.it/images/logowhite.pnghttp://eprints.imtlucca.it/2018-01-16T10:10:51Z2018-01-16T10:10:51Zhttp://eprints.imtlucca.it/id/eprint/3862This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/38622018-01-16T10:10:51ZMulti-parametric sensitivity analysis of the band structure for tetrachiral acoustic metamaterialsTetrachiral materials are characterized by a cellular microstructure made by a periodic pattern of stiff rings and flexible ligaments. Their mechanical behaviour can be described by a planar lattice of rigid massive bodies and elastic massless beams. The periodic cell dynamics is governed by a monoatomic structural model, conveniently reduced to the only active degrees-of-freedom. The paper presents an explicit parametric description of the band structure governing the free propagation of elastic waves. By virtue of multiparametric perturbation techniques, sensitivity analyses are performed to achieve an analytical asymptotic approximation of the dispersion functions. The parametric conditions for the existence of full band gaps in the low-frequency range are established. Furthermore, the band gap amplitude is analytically assessed in the admissible parameter range. In tetrachiral acoustic metamaterials, stop bands can be opened by the introduction of intra-ring resonators. Perturbation methods can efficiently deal with the consequent enlargement of the mechanical parameter space. Indeed high-accuracy parametric approximations are achieved for the band structure, enriched by the new optical branches related to the resonator frequencies. In particular, target stop bands in the metamaterial spectrum are analytically designed through the asymptotic solution of inverse spectral problems.Marco LepidiAndrea Bacigalupoandrea.bacigalupo@imtlucca.it2017-09-18T12:18:33Z2017-09-18T12:18:33Zhttp://eprints.imtlucca.it/id/eprint/3788This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/37882017-09-18T12:18:33ZAnalytical and computational methods for modeling mechanical filters against bloch wave propagationThe free propagation of elastic waves through periodic microstructured materials
can be studied by the analytical formulation of beam lattice models for the elementary cell, in
combination with the Floquet-Bloch theory. Within this framework, the present paper deals
with periodic tetrachiral materials characterized by a monoatomic cell. Alternative analytical
formulations can be developed by continualization-homogenization techniques in micropolar
equivalent continua, characterized by overall elastic and inertial tensors. Valid approaches
for the solution of the wave propagation problems are offered by perturbation methods, numerical
continuation techniques, and – finally – computational analyses, suited to account for
some mechanical updates or improvements that can hardly be included in synthetic formulations.
Based on these considerations, the dispersion curves achievable by different formulations
are compared and discussed. The major interest is focused on the spectral effects
determined by changes in the geometry, inertia, elasticity of the microstructural elements and,
finally, by variations in the cellular symmetry. Some attention is paid to the parameter combinations,
which might open band gaps in the low-frequency range, useful to filter undesired
dynamic signals for vibration shielding purposes.Francesca VadalàAndrea Bacigalupoandrea.bacigalupo@imtlucca.itMarco LepidiLuigi Gambarotta2017-01-30T10:33:52Z2017-01-30T11:33:18Zhttp://eprints.imtlucca.it/id/eprint/3647This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/36472017-01-30T10:33:52ZLattice orientation and crack size effect on the mechanical properties of GrapheneThe effect of lattice orientation and crack length on the mechanical properties of Graphene are studied based on molecular dynamics simulations. Bond breaking and crack initiation in an initial edge crack model with 13 different crack lengths, in 10 different lattice orientations of Graphene are examined. In all the lattice orientations, three recurrent fracture patterns are reported. The influence of the lattice orientation and crack length on yield stress and yield strain of Graphene is also investigated. The arm-chair fracture pattern is observed to possess the lowest yield properties. A sudden decrease in yield stress and yield strain can be noticed for crack sizes <10 nm. However, for larger crack sizes, a linear decrease in yield stress is observed, whereas a constant yield strain of ≈≈0.05 is noticed. Therefore, the yield strain of ≈≈0.05 can be considered as a critical strain value below which Graphene does not show failure. This information can be utilized as a lower bound for the design of nano-devices for various strain sensor applications. Furthermore, the yield data will be useful while developing the Graphene coating on Silicon surface in order to enhance the mechanical and electrical characteristics of solar cells and to arrest the growth of micro-cracks in Silicon cells.Pattabhi R. Budarapupattabhi.budarapu@imtlucca.itB. JavvajiV. K. SutrakarD. Roy MahapatraMarco Paggimarco.paggi@imtlucca.itG. ZiT. Rabczuk2016-03-14T14:23:16Z2016-03-14T14:23:16Zhttp://eprints.imtlucca.it/id/eprint/3229This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/32292016-03-14T14:23:16ZStroh formalism in analysis of skew-symmetric and symmetric weight functions for interfacial cracksThe focus of the article is on analysis of skew-symmetric weight matrix functions for interfacial cracks in two dimensional anisotropic solids. It is shown that the Stroh formalism proves to be an efficient approach to this challenging task. Conventionally, the weight functions, both symmetric and skew-symmetric, can be identified as a non-trivial singular solutions of the homogeneous boundary value problem for a solid with a crack. For a semi-infinite crack, the problem can be reduced to solving a matrix Wiener-Hopf functional equation. Instead, the Stroh matrix representation of displacements and tractions, combined with a Riemann-Hilbert formulation, is used to obtain an algebraic eigenvalue problem, that is solved in a closed form. The proposed general method is applied to the case of a quasi-static semi-infinite crack propagation between two dissimilar orthotropic media: explicit expressions for the weight matrix functions are evaluated and then used in the computation of complex stress intensity factor corresponding to an asymmetric load acting on the crack faces.Lorenzo Morinilorenzo.morini@imtlucca.itEnrico RadiAlexander MovchanNatalia Movchan2016-03-11T13:18:00Z2016-03-11T13:18:00Zhttp://eprints.imtlucca.it/id/eprint/3221This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/32212016-03-11T13:18:00ZOn fracture criteria for dynamic crack propagation in elastic materials with couple stressesThe focus of the article is on fracture criteria for dynamic crack propagation in elastic materials with microstructures. Steady-state propagation of a Mode III semi-infinite crack subject to loading applied on the crack surfaces is considered. The micropolar behavior of the material is described by the theory of couple-stress elasticity developed by Koiter. This constitutive model includes the characteristic lengths in bending and torsion, and thus it is able to account for the underlying microstructures of the material. Both translational and micro-rotational inertial terms are included in the balance equations, and the behavior of the solution near to the crack tip is investigated by means of an asymptotic analysis. The asymptotic fields are used to evaluate the dynamic J-integral for a couple-stress material, and the energy release rate is derived by the corresponding conservation law. The propagation stability is studied according to the energy-based Griffith criterion and the obtained results are compared to those derived by the application of the maximum total shear stress criterion.Lorenzo Morinilorenzo.morini@imtlucca.itAmdrea PiccolroazGennady MishurisEnrico Radi2016-03-11T12:10:25Z2016-05-04T09:55:02Zhttp://eprints.imtlucca.it/id/eprint/3214This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/32142016-03-11T12:10:25ZConservation integrals for two circular holes kept at different temperatures in a thermoelastic solidAbstract An explicit analytic solution for thermal stresses in an infinite thermoelastic medium with two circular cylindrical holes of different sizes kept at different constant temperatures, under steady-state heat flux is presented. The solution is obtained by using the most general representation of a biharmonic function in bipolar coordinates. The stress field is decomposed into the sum of a particular stress field induced by the steady-state temperature distribution and an auxiliary isothermal stress field required to satisfy the boundary conditions on the holes. The variations of the stress concentration factor on the surface of the holes are determined for varying geometry of the holes. The concept of the conservation integrals Jk, M and L is extended to steady state thermoelasticity and the integrals are proved to be path-independent. These integrals are calculated on closed contours encircling one or both holes. The geometries of a hole in a half-space and an eccentric annular cylinder are considered as particular cases.Enrico RadiLorenzo Morinilorenzo.morini@imtlucca.itI. Sevostianov2015-12-11T11:32:28Z2015-12-11T11:32:28Zhttp://eprints.imtlucca.it/id/eprint/2970This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/29702015-12-11T11:32:28ZSize-Scale Effects on the Friction Coefficient: From Weak Faults at the Planetary Scale to Superlubricity at the NanoscaleIn the present paper, two size-effect laws for the friction coefficient of rough surfaces are proposed and compared. The former is based on purely dimensional analysis arguments and is related to the fractality of the contact domains. This scaling law applies from the macro to the planetary scales, where contact is almost elastic. The latter, holding at the micro and nanoscales, is based on the adhesion theory of friction and assumes that the friction resistance is governed by the strong adhesive bonds at the asperities, caused by elasto-plastic deformations. Whereas the fractal scaling law suggests a friction coefficient decreasing with the size of the nominal contact area, the opposite trend is predicted by the adhesion theory. The application of these two scaling laws to Zircalloy (Zr-4), Stainless Steel (SS304) and Nickel (Ni200) permits to determine the scale range of validity of each scaling law and to show that they may coexist. Finally, it is found that the length scale which marks the transition between the two regimes is a function of the plasticity index proposed by Mikic.Marco Paggimarco.paggi@imtlucca.itAlberto Carpinteri2015-11-02T14:43:10Z2015-11-02T14:43:10Zhttp://eprints.imtlucca.it/id/eprint/2803This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/28032015-11-02T14:43:10ZAn Accurate Thermoviscoelastic Rheological Model for Ethylene Vinyl Acetate Based on Fractional CalculusThe thermoviscoelastic rheological properties of ethylene vinyl acetate (EVA) used to embed solar cells have to be accurately described to assess the deformation and the stress state of photovoltaic (PV) modules and their durability. In the present work, considering the stress as dependent on a noninteger derivative of the strain, a two-parameter model is proposed to approximate the power-law relation between the relaxation modulus and time for a given temperature level. Experimental validation with EVA uniaxial relaxation data at different constant temperatures proves the great advantage of the proposed approach over classical rheological models based on exponential solutions.Marco Paggimarco.paggi@imtlucca.itAlberto Sapora2013-11-25T10:49:20Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1941This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19412013-11-25T10:49:20ZLa forma del provino ed il problema del contatto nella valutazione della resistenza del calcestruzzoFerdinando IndelicatoMarco Paggimarco.paggi@imtlucca.it