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October 2014 - February 2015

## Publications

Publications (130)

This paper presents the preliminary results of an experimental programme on the tensile performance of flax-TRM systems subjected to accelerated ageing. Composites consisting of two layers of flax textiles embedded in a lime-based mortar were conditioned in water for 1000 h and 2000 h at controlled temperatures of 23oC and 40oC. Bare textiles were...

The present work is devoted to prove that unstable crack propagation events do not comply with quasi-static hypotheses and thus should be modelled by dynamic approaches. Comprehensive supporting evidence is provided on the basis of three different analyses conducted on multi-ligament unstable fracture conditions, including a simplified Spring-Mass...

The present work aims at investigating crack shielding and size effect related to a cracked slab under tensile loading. For this purpose, experimental tests are carried out on PMMA cracked samples. Three different geometries are taken into account, presenting one, two or three parallel edge cracks, and assuming their distance equal to their initial...

This study introduces a novel approach to analyze the stress and displacement fields around blunt notches in bi-material media, focusing on mode III loading conditions. The eigenfunction expansion method is used to derive a simplified yet accurate solution, satisfying the boundary conditions for bi-material blunt V-notches. The robustness of the pr...

In this paper, the coupled Finite Fracture Mechanics criterion is extended to assess the finite fatigue life of orthotropic notched laminated composites. The approach is validated through a comprehensive experimental program conducted on laminated composites under tension-tension cyclic loading conditions with two distinct lay-ups. For a given load...

With the main purpose of obtaining lightweight and durable structures, bonding techniques have improved significantly in several industries. Depending on the type of structure, joining different components with different materials may require different joint geometries, which may perform better or worse. Still, only the bond performance of a very l...

This work presents a coupled approach, based on Finite Fracture Mechanics (FFM), to preliminarily investigate hydraulic fracturing of rocks. The novelty of the criterion relies on the assumption of a finite crack extension and on the simultaneous fulfillment of a stress requirement and the energy balance. Two material constants are involved, namely...

The phenomenon of brittle crack onset stemming from a circular hole in an infinite plate subjected to remote biaxial loading is herein investigated. A thorough analysis on the influence of the loading biaxiality reveals the existence of a wide casuistry in the sign and trend distributions of the stress field and Stress Intensity Factor, thus render...

A novel model is proposed to assess the fatigue lifetime of notched components under uniaxial loading conditions in the medium/high-cycle fatigue regime. It is based on the Finite Fracture Mechanics approach, previously proposed in static and fatigue limit frameworks, according to which failure occurs when a stress and an energy condition are simul...

The present work aims at investigating the failure size effect of a spheroidal void in an infinite linear elastic solid under remote tension by means of the coupled Finite Fracture Mechanics (FFM) approach. The opening stress field and the stress intensity factor (SIF) of an annular crack surrounding the cavity —necessary for the FFM implementation...

The coupled criterion of Finite Fracture Mechanics (FFM) has already been successfully applied to assess the brittle failure initiation in cracked and notched structures subjected to quasi-static loading conditions. The FFM originality lies in addressing failure onset through the simultaneous fulfilment of a stress requirement and the energy balanc...

In the present paper we review and compare several analytical models describing the single-lap shear test, which is the most common test to determine the bonding behaviour between a strengthening FRP plates and the concrete substrate. The models are one-dimensional and formulated under the assumption that debonding occurs as a pure mode II cracking...

Finite Fracture Mechanics and Cohesive Crack Model can effectively predict the strength of plain, cracked or notched structural components, overcoming the classical drawbacks of Linear Elastic Fracture Mechanics. Aim of the present work is to investigate size effects by expressing each model as a unified system of two equations, describing a stress...

The brittle failure behavior of a solid containing a Penny-shaped crack and subjected to mode I loading conditions is investigated. The analysis is performed in a semi-analytical way by implementing different approaches: the coupled criterion of Finite Fracture Mechanics (FFM) and the Cohesive Zone Model (CZM). Results are compared in terms of the...

The development of robust failure criteria suitable for predicting crack initiation under both quasi-static and dynamic loading conditions has always garnered attention in the scientific community due to its positive impact in the trustworthiness of the failure predictions for critical structural applications. In this sense, the present work applie...

Two nonlocal approaches are applied to the borehole geometry, i.e. a circular hole in an infinite elastic medium subjected to internal pressure. The former approach lays in the framework of Gradient Elasticity (GE), which results nonlocal in the strict sense, being based on a nonlocal constitutive relationship. Changing the stress field as the geom...

External bonding of composite reinforcements has become an accepted method for strengthening the existing structures, e.g., FRCM to concrete. In the present manuscript, the shear lag model is combined with two different bond-slip laws to investigate the mechanics of debonding of composite-to-substrate joints by considering the residual strength. Bo...

Interfacial debonding in fiber-reinforced composites is a common problem, especially in external strengthening techniques. This investigation aims to determine the load during debonding, and discusses two practical design parameters for direct shear tests, which are commonly used to assess the mechanics of debonding. In this study, three different...

The decrease of the apparent uniaxial tensile strength resulting from a single flawless spherical cavity in an infinite linear elastic continuum under uniaxial tension is investigated. To this end, a new generalized semianalytical expression for the stress intensity factor of an annular crack surrounding the spherical cavity under different loading...

Two nonlocal approaches are applied to the borehole geometry, herein simply modelled as a circular hole in an infinite elastic medium, subjected to remote biaxial loading and/or internal pressure. The former approach lies within the framework of Gradient Elasticity (GE). Its characteristic is nonlocal in the elastic material behaviour and local in...

Mixed mode crack initiation in PMMA specimens containing square holes is investigated experimentally by uniaxial tensile tests. The crack deflection with respect to the V-notch bisector and the failure load both increase for decreasing hole sizes, to which correspond higher mode mixities. In order to catch this behavior from a theoretical point of...

In the present contribution, the coupled stress-energy criterion of Finite Fracture Mechanics (FFM) is applied to assess the fatigue limit of structures weakened by sharp V- and U-notches and subjected to mode I loading conditions. The FFM is a critical-distance-based approach whose implementation requires the knowledge of two material properties,...

The apparent weakening of a uniaxially tensioned infinite domain that contains a single spherical void and is anywhere else filled with a homogeneous and linear elastic material is investigated through two Finite Fracture Mechanics approaches. Resultant charts depicting the respectively predicted relation of the weakening ratio with the void’s radi...

A new numerical procedure for predicting interface failures between solids is developed. The procedure is based on the Linear Elastic-(Perfectly) Brittle Interface Model (LEBIM) combined with the Coupled Criterion of the Finite Fracture Mechanics (CCFFM). Although in the present investigation this procedure is implemented in a 2D BEM code, a genera...

The fatigue limit of structures containing V- and U-notches is assessed through the coupled stress-energy criterion of Finite Fracture Mechanics (FFM). The analysis is limited to mode I loading conditions. The FFM criterion is a critical-distance-based approach whose implementation requires the knowledge of two material properties, namely the plain...

The paper investigates the fatigue feature sensitivity, considering the two standard cases of a center-through thickness sharp crack and a circular notch by the coupled criterion of Finite Fracture Mechanics (FFM). Similarly to other criteria based on a critical distance, the FFM approach involves two parameters: the plain specimen fatigue limit, a...

In this brief note, we provide the failure stress of a solid containing a penny-shaped crack by means of Finite Fracture Mechanics. The solution is analytical up to the numerical root of the equation providing the finite crack growth increment. Results are discussed and compared with the ones provided by Linear Elastic Fracture Mechanics, by Theory...

An analytical procedure predicting a debond (interface crack) onset and growth in an adhesive joint between two beams or plates is developed and applied to a specific configuration often used in reinforcement tests in civil engineering. The procedure is based on Timoshenko beam theory and Linear Elastic-(Perfectly) Brittle Interface Model (LEBIM) c...

The paper investigates the fatigue crack/notch sensitivity by the coupled criterion of Finite Fracture Mechanics (FFM). The approach involves two parameters: the plain specimen fatigue limit, and the threshold value of the stress intensity factor range for fatigue crack growth. Useful analytical relationships are presented. The accuracy of FFM is v...

The brittle crack initiation from a circular hole in an infinite slab subjected to remote biaxial loading is investigated by means of the coupled finite fracture mechanics criterion, focussing on the behaviour of the average energy release rate. The work then analyzes the stability/instability of crack growth, following the terminology put forward...

The present work represents the prosecution of a previous paper [Short cracks and V-notches: Finite Fracture Mechanics vs. Cohesive Crack Model (2016). P. Cornetti, A. Sapora, A. Carpinteri. Engineering Fracture Mechanics 168:2–12] aiming to corroborate the use of Finite Fracture Mechanics by showing that its failure load estimates are very close t...

The brittle crack initiation from a circular hole in an infinite slab under uniaxial remote tensile load is investigated. The analysis consists of two parts. The former is focused on the difference between symmetric and asymmetric crack propagation. Different criteria in the framework of the Theory of Critical Distances are implemented, and the pot...

After more than one century since the well-known work by Kirsch (1898) on the stress field around a circular hole subjected to remote tensile load, the problem of the related size effects has recently come back to the scientific attention. Indeed, some relevant discrepancies have been detected between experimental results obtained by means of ad-ho...

Brittle fracture tests are carried out on Brazilian disk specimens containing a circular hole. The experimental campaign involves two different polymeric materials, Polymethyl-methacrylate (PMMA) and general-purpose Polystyrene (GPPS), respectively. Keeping fixed the disk diameter, five different hole sizes are tested for each material sample, thus...

In this paper we focus on the prediction of mode-I debonding for a double cantilever beam (DCB). Among the various modeling approaches available, the Cohesive Crack Model (CCM) and Finite Fracture Mechanics (FFM) are selected for the analytical investigation, due to their ability to reconcile the stress- and energy-based approaches. The specimen is...

Around 1970 quenching AISI 4340 steel from 1200 °C was discovered to lead to much higher fracture toughness, in the as quenched state, than by conventional austenitizing at 870 °C. Further researches have ascertained that the apparent toughness increase is limited to fracture toughness tests, whereas Charpy-V impact tests do not show any betterment...

The aim of the present paper is to study the interaction between two aligned fibres embedded in a large matrix. Special attention is taken to the influence of the presence of a second fibre on the fibre-matrix interface failure. The Linear Elastic Brittle Interface Model (LEBIM) is used to model the fibre-matrix interface behaviour. In LEBIM, an un...

When dealing with mixed-mode brittle fracture of cracked elements, T-stress affects both the stress field and the energy balance. This problem is investigated here through the coupled Finite Fracture Mechanics (FFM) criterion by varying mode mixity of the main crack. Results are presented in terms of the critical stress intensity factors (SIF) and...

T-stress effects on crack deflection in notched brittle materials are investigated by means of an average stress approach. It is shown that the crack advance always reveals to be straight if the T contribution is negligible. On the contrary, if T is different from zero, the trajectory tends to curve: the higher is |T|, the larger is the curvature p...

One-dimensional diffusion problems in bounded porous media characterized by the presence of nonlocal interactions are investigated by assuming a Darcy's constitutive equation of convolution integral type. A power law attenuation function is implemented: Analogies and differences of the flow-rate-pressure law with respect to other nonlocal and fract...

A three-parameter fractional model, composed by a springpot in series with a dapshpot, was employed to describe the rheological behaviour of a set of polymer-modified bituminous binders obtained by combining a single-base bitumen with different types of syrene-butadiene-styrene copolymers at different concentrations. Experimental strain-time curves...

In recent years, Finite Fracture Mechanics has proven to be an effective tool to estimate the strength of mechanical components, allowing fast strength predictions suitable for preliminary sizing and optimization of structures. In the present paper, we intend to corroborate the Finite Fracture Mechanics approach by showing that failure load estimat...

The combination of brittleness in materials and stress concentrations may lead to premature fracture of structural components. To improve the modelling capability more and more sophisticated methods have to be employed. To the purpose a Finite Fracture Mechanics (FFM) criterion based on the contemporaneous fulfilment of a stress requirement and the...

Around 1970 it was discovered that quenching AISI 4340 steel from 1200 °C leads to much higher fracture toughness, in the as quenched state, than by conventional austenitizing at 870 °C. Further researches have ascertained that the apparent toughness increase is limited to fracture toughness tests (KIC), whereas Charpy-V impact tests do not show an...

A fracture criterion able to predict the failure loads producing crack onset and propagation along weak interfaces between solids is presented. The procedure is based on the Linear Elastic-(Perfectly) Brittle Interface Model (LEBIM) combined with a Finite Fracture Mechanics (FFM) approach. The procedure imposes the simultaneous fulfillment of two c...

The coupled Finite Fracture Mechanics (FFM) criterion is applied to investigate brittle fracture in rounded V-notched samples under mode I loading. The approach is based on the contemporaneous fulfilment of a stress requirement and the energy balance, the latter being implemented on the basis of a recently proposed analytical expression for the str...

Fitting of experimental creep-recovery curves obtained from rheological tests carried out on viscoelastic materials can reveal difficulties when handled by classical rheological theories, which generally provide exponential-type functions requiring a great number of parameters to be determined. Fractional calculus may represent a natural framework...

An analytical expression for the Stress Intensity Factor (SIF) related to a crack emanating from a blunted V-notch root is put forward. Different notch amplitudes, ranging from 0° to 180°, and different crack length to root radius ratios, ranging from 0 to 10, are taken into account. The analysis is limited to mode I loading conditions, as long as...

A method for the prediction of crack onset and propagation along an interface in a fibre-reinforced composite system is devel- oped. The method is based on the Linear Elastic-(Perfectly) Brittle Interface Model (LEBIM) and a coupled stress and energy criterion of the Finite Fracture Mechanics (FFM). Models similar to LEBIM, also called weak or impe...

Fractional calculus is the mathematical subject dealing with integrals and derivatives of noninteger order. Although its age approaches that of classical calculus, its applications in mechanics are relatively recent and mainly related to fractional damping. Investigations using fractional spatial derivatives are even newer. In the present paper spa...

This paper focuses on the prediction of edge debonding for a beam retrofitted with a Fiber-Reinforced Polymer plate. This failure mechanism, also known as plate-end debonding, stems from the concentration of interfacial stresses arising at the termination of the strengthening plate. Early models of edge debonding adopted failure criteria based on i...

An analytical expression for the stress intensity factor related to a crack stemming from a blunted V-notch tip is put forward. The analysis is limited to mode I loading conditions, as long as the crack length is sufficiently small with respect to the notch depth. The proposed formula improves significantly the predictions of a recently introduced...

We apply the Finite Fracture Mechanics criterion to address the problem of a V-notched structure subjected to mode II loading, i.e., we provide a way to determine the direction and the load at which a crack propagates from the notch tip and express the critical conditions in terms of the generalized stress intensity factor. Weight functions for V-n...

In recent years, Finite Fracture Mechanics has proven to be an effective tool to predict the strength of mechanical components. Since the proposed method rests on a linear elastic solution, it allows fast strength predictions suitable for preliminary sizing and optimization of plain or composite structures. While several contributions in the Scient...

In this paper, the nonlocal diffusion in one-dimensional continua is investigated by means of a fractional
calculus approach. The problem is set on finite spatial domains and it is faced numerically by means of
fractional finite differences, both for what concerns the transient and the steady-state regimes. Nonlinear
deviations from classical solut...

Aim of the present paper is twofold. On one hand, we apply the Finite Fracture Mechanics criterion to address the problem of a V-notched structure subjected to a mixed-mode loading, i.e. we provide a way to determine the direction and the load at which a crack propagates from the notch tip. On the other hand, we make use of the formalism recently i...

In the present paper, the wave propagation in one-dimensional elastic continua, characterized by nonlocal interactions modeled by fractional calculus, is investigated. Spatial derivatives of non-integer order 1 < α < 2 are involved in the governing equation, which is solved by fractional finite differences. The influence of long-range interactions...

This paper focuses on the prediction of edge debonding for a concrete beam retrofitted with a fiber-reinforced polymer plate. This failure mechanism, also known in the literature as plateend debonding, stems from the concentration of interfacial stresses arising at the termination of the strengthening plate. Early models of edge debonding adopted f...

In the present paper we analyze the competition between different failure mechanisms in fiber reinforced polymer (FRP) strengthened beams. Attention is focused on a three-point bending test of a concrete specimen reinforced by a FRP strip at the bottom. We analyze the competition between the growth of a flexural crack in the concrete beam along its...

In asserting structural safety it is of paramount importance to be able to evaluate the loading capacity of notched components, where stresses concentrate and can trigger cracks leading to a catastrophic failure or to a shortening of the assessed life of the structure. Restricting the analysis to brittle materials, we apply the Finite Fracture Mech...

Finite Fracture Mechanics (FFM) criterion is formalized to predict the critical failure
loads of brittle U-notched specimens, subjected to mode I loading. The criterion, recently
applied to V-notched structures, requires the contemporaneous fulfilment of stress
requirements and energy conditions for fracture to propagate: the stress field ahead of...

In the present paper we provide a method to determine the load causing delamination along an interface in a composite structure. The method is based on the elastic interface model, according to which the interface is equivalent to a bed of linear elastic springs, and on Finite Fracture Mechanics, a crack propagation criterion recently proposed for...

Finite Fracture Mechanics (FFM) is applied to investigate the brittle failure behavior of rounded V-notched elements subjected to mode I loading. According to the criterion, fracture does not propagate continuously, but by finite crack extensions, whose value is determined by the contemporaneous fulfilment of a stress requirement and an energy bala...

Among rehabilitation strategies, bonding of Fibre Reinforced Polymers (FRP) plates is becoming more and more popular, especially for what concerns concrete structures. The performance of the interface between FRP and concrete is one of the key factors affecting the behaviour of the strengthened structure. Up to now, closed-form analytical solutions...

If the attenuation function of strain is expressed as a power law, the formalism of fractional calculus may be used to handle
Eringen nonlocal elastic model. Aim of the present paper is to provide a mechanical interpretation to this nonlocal fractional
elastic model by showing that it is equivalent to a discrete, point-spring model. A one-dimension...

In this work, the anisotropic linear elastic properties of two-phase composite materials, made up of square inclusions embedded in a matrix, are investigated. The inclusions present a fractal hierarchical distribution and are supposed to have the same Poisson's ratio as the matrix but a different Young's modulus. The effective elastic moduli of the...

The determination of the failure load for brittle or quasi-brittle specimens containing a re-entrant corner has been faced by several authors, whose approaches are available in the Scientific Literature. However, up to now, little attention has been paid to the presence of a minimum, i.e. an angle at which the critical load attains its minimum valu...

In this paper the results of a series of three-point bending experimental tests for specimens made of polystyrene and containing re-entrant corners are firstly presented. Tests involved different notch angles, different notch depths and finally different dimensions of the samples. Because of the structural brittleness, the generalized stress intens...

Fracture in brittle material specimens with V-notches is satisfactorily described assuming as governing parameter the generalized (or notch) stress intensity factor, whose anomalous physical dimensions depend on the notch opening angle. Its critical value, i.e. the generalized toughness, can then be linked to the material strength and toughness acc...

Several enriched continuum mechanics theories have been proposed by the scientific community in order to develop models capable of describing microstructural effects. The aim of the present paper is to revisit and compare two of these models, whose common denominator is the use of fractional calculus operators. The former was proposed to investigat...

The application of the external reinforcement makes rather complex the scenario of the possible failure modes in reinforced concrete beams retrofitted with FRP. The far more commonly observed failure modes are: (i) edge debonding of the FRP sheet, (ii) intermediate crack induced debonding and (iii) beam failure due to diagonal (shear) crack propaga...

In the present paper we analyse the edge debonding failure of a beam strengthened by a fibre reinforced polymer. As well known from the literature, a stress concentration is found at the edge of the reinforcement which triggers the debonding of the fibre reinforced polymer strip when the load reaches a certain critical threshold. Two failure criter...

In this paper the results of a series of experimental tests upon three-point bending specimens
made of polystyrene and containing re-entrant corners are firstly described. Tests involved different notch
angles, different notch depths and finally different sizes of the samples. All the specimens broke at the
defect, as expected because of the materi...