Rosa Penna

Nano-beams under torsion: a stress-driven nonlocal approach

Purpose This study aims to model scale effects in nano-beams under torsion. Design/methodology/approach The elastostatic problem of a nano-beam is formulated by a novel stress-driven nonlocal approach. Findings Unlike the standard strain-driven nonlocal methodology, the proposed stress-driven nonlocal model is mathematically and mechanically consistent. The contributed results are useful for the design of modern devices at nanoscale. Originality/value The innovative stress-driven integral nonlocal model, recently proposed in literature for inflected nano-beams, is formulated in the present submission to study size-dependent torsional behavior of nano-beams.

Investigations for Thermal and Electrical Conductivity of ABS-Graphene Blended Prototypes

The thermoplastic materials such as acrylonitrile-butadiene-styrene (ABS) and Nylon have large applications in three-dimensional printing of functional/non-functional prototypes. Usually these polymer-based prototypes are lacking in thermal and electrical conductivity. Graphene (Gr) has attracted impressive enthusiasm in the recent past due to its natural mechanical, thermal, and electrical properties. This paper presents the step by step procedure (as a case study) for development of an in-house ABS-Gr blended composite feedstock filament for fused deposition modelling (FDM) applications. The feedstock filament has been prepared by two different methods (mechanical and chemical mixing). For mechanical mixing, a twin screw extrusion (TSE) process has been used, and for chemical mixing, the composite of Gr in an ABS matrix has been set by chemical dissolution, followed by mechanical blending through TSE. Finally, the electrical and thermal conductivity of functional prototypes prepared from composite feedstock filaments have been optimized.

A Note on Torsion of Nonlocal Composite Nanobeams

The Eringen elastic constitutive relation is used in this paper in order to assess small-scale effects in nanobeams. Structural behavior is studied for functionally graded materials in the cross-sectional plane and torsional loading conditions. The governing boundary value problem has been formulated in a mixed framework. Torsional rotations and equilibrated moments are evaluated by solving a first-order differential equation of elastic equilibrium with boundary conditions of kinematic-type. Benchmarks examples are briefly discussed, enlightening thus effectiveness of the proposed methodology.

On Bending of Bernoulli-Euler Nanobeams for Nonlocal Composite Materials

Evaluation of size effects in functionally graded elastic nanobeams is carried out by making recourse to the nonlocal continuum mechanics. The Bernoulli-Euler kinematic assumption and the Eringen nonlocal constitutive law are assumed in the formulation of the elastic equilibrium problem. An innovative methodology, characterized by a lowering in the order of governing differential equation, is adopted in the present manuscript in order to solve the boundary value problem of a nanobeam under flexure. Unlike standard treatments, a second-order differential equation of nonlocal equilibrium elastic is integrated in terms of transverse displacements and equilibrated bending moments. Benchmark examples are developed, thus providing the nonlocality effect in nanocantilever and clampled-simply supported nanobeams for selected values of the Eringen scale parameter.

ACCURATE NUMERICAL METHODS FOR STUDYING THE NONLINEAR WAVE-DYNAMICS OF TENSEGRITY METAMATERIALS

This paper presents presents an effective numerical approach to the nonlinear dynamics of columns of tensegrity prisms subject to impulsive compressive loading. The equations of motions of the analyzed structures are formulated in vector form, by modeling the cables as deformable members and the bars as rigid bodies. The given numerical results investigate the wave dynamics of tensegrity columns, with focus on the propagation of compression solitary waves with variable size and amplitude throughout the system, as a function of the applied impact velocity and the state of prestress of the structure. The engineering potential of the examined structures as tunable acoustic actuators is discussed. 3911 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 3911-3922

ADVANCED NUMERICAL MODELS FOR THE ANALYSIS OF UNREINFORCED AND STRENGTHENED MASONRY VAULTS

Masonry buildings realized in the last centuries are a significant part of the international architectural heritage. The optimal design of the retrofit interventions of these buildings represents a priority and requires the evaluation of their mechanical behavior under static and dynamic loads. Several mechanical models capable to study masonry structures are available in literature and are based on Heyman limit analysis approach. These models cannot be easily adopted within FEM codes. Within this context, a Genetic Algorithm is implemented within a refinement adaptive finite element model to computational mesh of shell surfaces. The proposed model researches a ‘safe’ thrust surface of a masonry vault within a design domain, by minimizing the average value of the principal tensile stresses carried by the unreinforced portion of the material (fitness function). The design domain coincides with either the vault volume, in the case of unreinforced masonry members, or an external region of the vault in correspondence with the reinforced portions, in the case of the vault strengthened with either Fiber Reinforced Polymer or Fabric Reinforced Cementitious composites. The proposed methodology allows evaluating the structural safety of masonry vault and defining an optimal design of reinforcement pattern. 5056 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 5056-5069

2D LATTICE STRUCTURES - A PARAMETRIC ANALYSIS

As discussed in a number of papers, both the static and the dynamic response of square lattice materials are strongly affected by the inner microstructure. It is worth noting that results obtained without considering this influence are totally misleading, especially if non-uniform changes in terms of stresses and strains are concerned at the local scale. Within this context, the present work focuses on a parametric analysis aimed at evaluating the influence of the main mechanical properties of RUC on the dynamic response of a 2D square lattice, thus extending previous results towards the condition of a possible different nonuniform mass density distribution over the RUC configuration. The existence of the band gaps within the low frequency region is searched as well as the position and width of the existing gaps are evaluated by means of a numerical strategy already developed and tested. 4986 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 4986-4999