Francesco Freddi

Mortar joints influence in debonding of masonry element strengthened with FRP

The effects of mortars joints in masonry substrate reinforced with FRP is investigated from the numerical point of view. The analysis has been conducted by means of a new interface model specifically developed to reproduce the debonding process occurring between an elastic thin body in adhesion with a cohesive support material, as concrete or masonry. The model accounts for mode I and mode II of failure, considering the effect of the in-plane deformation of the interface, i.e. the possible elongation or confinement of the material constituting the interface. Numerical results are compared with experimental evidences showing the good performances of the proposed model in investigating the transferring phenomena in heterogeneous interfaces and, in particular, in studying the influence of the presence of mortar joints in the masonry texture in the debonding process.

Phase-field modelling of failure in hybrid laminates

Abstract 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 variational formulation of brittle fracture with regularised approximation of discontinuities for the two layers, (ii) cohesive law for the adhesive interface that connects the layers and (iii) robust and consolidated numerical strategy for the solution of the non-linear discretised problem. Explicit and well detailed simulations are shown for four peculiar failure mechanisms and the outcomes validated against experimental results available in literature. The model is able to discriminate among these different failure mechanisms according to the geometrical and mechanical properties of the hybrid composite. Both delamination of the adhesive interface is followed and crack patterns within the materials are fully determined. Finally, the proposed approach opens new perspective studies in higher dimension settings.

Mechanical behaviour of surface layer fibreglass-reinforced flexible pavements

The work presented in this paper aims at providing a better understanding of the mechanical response of surface layer fibreglass-reinforced flexible pavements. The surface reinforcement technique consists of installing a fibreglass grid in between the levelling layer (placed on the base course to seal and level the pre-existing distresses) and the wearing course (or overlay). Flexural fracture tests were performed on two-layered reinforced asphalt specimens composed of both levelling and wearing courses to simulate a real overlay structure. Three fibreglass grids characterised by different mechanical and/or geometrical properties were employed. Strain localisation and damage distribution were investigated using an in-house digital image correlation system capable of achieving highly accurate 2D full-field strain maps of the specimens during loading. Finally, an analytical model was developed on purpose to reproduce the mechanical response of the asphalt mixture-interlayer system.

Durability of bonded assemblies: A predictive theory coupling bulk and interfacial damage mechanisms

ABSTRACT An advanced model coupling bulk and interfacial damages is proposed in order to predict the durability of adhesively bonded joints. The underlying theory, based on the principle of virtual power, is briefly presented in the first part of the paper. The second part is devoted to the validation the cited theory. The model is first implemented to describe the damage behavior of bonded assemblies subjected to either homogeneous tension or shear loading conditions. In each case, the theoretical simulations are compared to experimental data obtained in the same configuration. Such comparisons yield objective indications on the validity of the model.

A nonlinear model for marble sulphation including surface rugosity: theoretical and numerical results

We consider an evolution system describing the phenomenon of marble sulphation of a monument, accounting of the surface rugosity. We first prove a local in time well posedness result. Then, stronger assumptions on the data allow us to establish the existence of a global in time solution. Finally, we perform some numerical simulations that illustrate the main feature of the proposed model.