Roberto Alessi

Roberto Alessi
Università di Pisa | UNIPI · Department of Civil and Industrial Engineering

PhD

About

28
Publications
16,466
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1,264
Citations
Additional affiliations
May 2017 - present
Sapienza University of Rome
Position
  • PostDoc Position
June 2015 - May 2016
Sapienza University of Rome
Position
  • PostDoc Position

Publications

Publications (28)
Article
Full-text available
This paper presents a novel variational phase-field model for different fracture processes in fully saturated porous media. As a key feature, the model employs a micromechanics-based theory for the description of brittle-tensile and compressive–ductile fracture. As such, the field variables are linked to physical mechanisms at the microcrack level,...
Article
Full-text available
This paper presents a framework for modeling failure in quasi-brittle geomaterials under different loading conditions. A micromechanics-based model is proposed in which the field variables are linked to physical mechanisms at the microcrack level: damage is related to the growth of microcracks, while plasticity is related to the frictional sliding...
Preprint
Full-text available
This paper presents a framework for modeling failure in quasi-brittle geomaterials under different loading conditions. A micromechanics-based model is proposed in which the field variables are linked to physical mechanisms at the microcrack level: damage is related to the growth of microcracks, while plasticity is related to the frictional sliding...
Article
Full-text available
This paper presents a modeling framework to describe the driving mechanisms of cyclic failure in brittle and ductile materials, including cyclic plasticity and fatigue crack growth. A variational model is devised using the energetic formulation for rate-independent systems, coupling a phase-field description of fatigue fracture to a cyclic plastici...
Article
Full-text available
In this work, the energetic formulation for rate-independent dissipative materials is extended to consider non-associative plasticity models. In associative models, the fulfilment of the principle of maximum dissipation naturally leads to a variational formulation of the evolution problem. This is no longer true for non-associative models, which ar...
Article
Full-text available
Composites made of reinforcing short fibers embedded into brittle matrices, like, e.g., fiber-reinforced concretes, exhibit enhanced strength and ductility properties. Their failure process induced by tensile loadings involves hardening and softening stages as a result of matrix multiple micro-cracking, due to stress bridging of fibers across matri...
Article
A novel variational framework to model the fatigue behavior of brittle materials based on a phase-field approach to fracture is presented. The standard regularized free energy functional is modified introducing a fatigue degradation function that effectively reduces the fracture toughness as a proper history variable accumulates. This macroscopic a...
Preprint
Full-text available
This paper presents a modeling framework to describe the driving mechanisms of cyclic failure in brittle and ductile materials, including cyclic plasticity and fatigue crack growth. A variational model is devised using the energetic formulation for rate-independent systems, coupling a phase-field description of fatigue fracture to a cyclic plastici...
Article
The phase-field approach regularizes the variational theory of fracture by approximating cracks with a smeared damage field. In this work, the attention is focused on those formulations approximating mode II fractures (shear fractures). In these models, only the deviatoric part of the strain elastic energy, penalized by the phase-field, drives the...
Article
Full-text available
A powerful numerical instrument, which reproduces the complex failure mechanisms of hybrid laminates under in-plane loading conditions, is developed within the framework of phase-field modelling. The ruptures, strongly influenced by geometrical and mechanical properties of the plies and affected by the state of stress, are arranged as delamination...
Article
Full-text available
We study the existence of quasistatic evolutions for a family of gradient damage models which take into account fatigue, that is the process of weakening in a material due to repeated applied loads. The main feature of these models is the fact that damage is favoured in regions where the cumulation of the elastic strain (or other relevant variables...
Preprint
Full-text available
A novel variational framework to model the fatigue behavior of brittle materials based on a phase-field approach to fracture is presented. The standard regularized free energy functional is modified introducing a fatigue degradation function that effectively reduces the fracture toughness as a proper history variable accumulates. This macroscopic a...
Preprint
Full-text available
We study the existence of quasistatic evolutions for a family of gradient damage models which take into account fatigue, that is the process of weakening in a material due to repeated applied loads. The main feature of these models is the fact that damage is favoured in regions where the cumulation of the elastic strain (or other relevant variables...
Article
Full-text available
The present paper aims at modeling complex fracture phenomena where different damaging mechanisms are involved. For this purpose, the standard one-variable phase-field/gradient damage model, able to regularize Griffith’s isotropic brittle fracture problem, is extended to describe different degradation mechanisms through several distinct damage vari...
Chapter
Full-text available
In the last few years, several authors have proposed different phase-field models aimed at describing ductile fracture phenomena. Most of these models fall within the class of variational approaches to fracture proposed by Francfort and Marigo [13]. For the case of brittle materials, the key concept due to Griffith consists in viewing crack growth...
Article
Full-text available
We propose a new variational fatigue phase-field model. The basic idea of the model is to let the fracture energy decrease as a suitably defined accumulated strain measure increases, which is obtained by introducing a dissipation potential which explicitly depends on the strain history. This amounts to a phenomenological description of a multitude...
Article
Full-text available
In this paper, the complex failure process of unidirectional hybrid laminates under uniaxial loading condition is reproduced and investigated by a one-dimensional phase-field model. The key ingredients of the approach, describing the mechanical response of a hybrid composite made of two different layers, are: (i) a phase-field method, based on a va...
Article
Full-text available
The challenging and innovative idea of realizing a table totally made of fiber-reinforced concrete is explored through an interdisciplinary research activity, where contributions coming from different fields (design, material science, experimental testing, numerical modeling) are combined. The paper describes the different phases of the study, star...
Article
Full-text available
Plasticity and damage are two fundamental phenomena in nonlinear solid mechanics associated to the development of inelastic deformations and the reduction of the material stiffness. Alessi et al. [5] have recently shown, through a variational framework, that coupling a gradient-damage model with plasticity can lead to macroscopic behaviours assimil...
Article
Full-text available
This work aims to discuss, in the simplest way, some open issues concerning the energetic formulation for the modeling of rate-independent processes by means of a simple one-dimensional example. Early and unphysical jumps are avoided taking advantage of a time reparametrization and enforcing an energy imbalance during time-discontinuous transitions...
Article
We propose a finite-deformation lattice model for carbon nanotubes (CNTs), in which an energetic cost is assigned to changes in bond lengths, bond angles, and dihedral angles, while atomic interactions are governed by a Reactive Empirical Bond-Order potential. For the first time, we consider the effect of severe traction and pressure applied simult...
Article
Full-text available
The hybridisation of fibres reinforced laminates, i.e., the combined use of two or more families of fibres, is an effective technique to achieve a pseudo-ductile response and overcome the inherent brittleness which limits the wider use of composite materials. In this paper, a one-dimensional analytical model for unidirectional hybrid laminates is d...
Article
Full-text available
This paper presents a variational framework for the three-dimensional macroscopic modelling of superelastic shape memory alloys in an isothermal setting. Phase transformation is accounted through a unique second order tensorial internal variable, acting as the transformation strain. Postulating the total strain energy density as the sum of a free e...
Article
Localization of the phase transformations in Shape Memory Alloys (SMA) wires are well known. Several experimental and theoretical studies appeared in the last years. In this work the problem is addressed by means of a variational approach within the framework of the modeling of rate-independent materials by the specification of a non-local free ene...
Article
Full-text available
In the framework of rate-independent systems, a family of elastic-plastic-damage models is proposed through a variational formulation. Since the goal is to account for softening behaviors until the total failure, the dissipated energy contains a gradient damage term in order to limit localization effects. The resulting model owns a great flexibilit...
Article
Full-text available
A variational formulation is proposed for a family of elastic-plastic-damage models within the framework of rate-independent materials. That consists first in defining the total energy which contains, in particular, a gradient damage term and a term which represents the plastic dissipation but depends also on damage. Then, the evolution law is dedu...
Thesis
Full-text available
In the framework of rate-independent systems, an elastic-plastic-damage model, aimed at the description of ductile fracture processes, is proposed and investigated through a variational formulation. A cohesive, or ductile, crack occurs when the displacement field suffers a discontinuity whilst still being associated to a non-vanishing tensile stres...
Article
This work deals with a study of the vibrational properties of carbon nanotube-reinforced composites by employing an equivalent continuum model based on the Eshelby–Mori–Tanaka approach. The theory allows the calculation of the effective constitutive law of the elastic isotropic medium (matrix) with dispersed elastic inhomogeneities (carbon nanotube...

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