Giulio Alfano

• PhD - Structural Engineering
• Reader (Senior Associate Professor) at Brunel University London

A thermodynamic derivation is presented for a fractional rate-dependent cohesive zone model recently proposed by the authors to combine damage and linear viscoelasticity. In this setting, the assumptions behind the initially proposed damage evolution law are revisited. In particular, in the original model damage evolution is driven only by the ener...

A cohesive zone model is formulated to describe the mechanics of initiation and propagation of cracks and the associated asperity degradation and nonlinear dilation along structural interfaces of quasi-brittle materials, such as concrete, rocks and masonry, subjected to monotonic or cyclic loading. Using a two-scale approach, a cohesive-law is dete...

This paper presents a novel formulation of a hereditary cohesive zone model able to effectively capture rate-dependent crack propagation along a defined interface, over a wide range of applied loading rates and with a single set of seven input parameters only, as testified by the remarkable agreement with experimental results in the case of a doubl...

It is widely accepted that for many buckling problems of plates and shells in the plastic range the flow theory of plasticity leads to a significant overestimation of the buckling stress while the deformation theory provides much more accurate predictions and is therefore generally recommended for use in practical applications. The present work aim...

This paper presents a novel rate-dependent cohesive-zone model combining damage and visco-elasticity and based on two fundamental assumptions. Firstly we postulate the existence of an intrinsic (i.e. rate-independent) fracture energy. Secondly, within a thermodynamically consistent damage-mechanics framework we assume that the evolution of the dama...

Ductile fracture in metals has been intensively studied over at least 8 decades and a number of relatively well established methods have been developed to characterise the fracture resistance of metal components in terms of critical fracture toughness parameter(s). The most widely used ‘fitness-for-service’ industry standards concerning evaluation...

Storing CO2 in deep saline aquifers is a key strategy for carbon capture and storage, an essential technology in the global effort to mitigate greenhouse gas emissions. Several mathematical and computational models have been proposed to simulate CO2 storage in geological formations [1-3]. These models aim to comprehensively capture the intricate in...

For adhesive joints, several authors questioned the applicability of LEFM when the combination between the ductility of the adhesive, the stiffness of the adherents and the fracture mode leads to a relatively large process zone during crack propagation. For such cases, nonlinear fracture mechanics (NLFM) and the use of the critical value, 𝐽𝑐, of th...

We present an experimental and numerical study of the rate dependence of the mode-I failure of adhesive joints, focussing on aluminium plates bonded with Araldite® 2015. For the experimental part, we tested 24 double-cantilever beams (DCB) at six different prescribed speeds, from 0.1 to 5000 mm/min. The numerical simulations use a previously propos...

Powell–Sabin B-splines, which are based on triangles, are employed in the framework of the extended finite element method (XFEM) for fracture analysis. This avoids the necessity of remeshing in discrete fracture models and increases the solution accuracy around the crack tip. Powell–Sabin B-splines are C1-continuous throughout the whole domain. The...

This paper addresses the experimental and numerical characterisation of the structural interface between titanium alloy Ti6Al4V plain bars and Normal (NWC) and Light-Weight Concrete (LWC) mixtures. Results of pull-out tests on ϕ 8 and ϕ 16 mm rebars from NWC and LWC batches and SEM analyses show that, although the employed rebars are plain, the deb...

In this work we develop a complete analytical solution for a double cantilever beam (DCB) where the arms are modelled as Timoshenko beams, and a bi-linear cohesive-zone model (CZM) is embedded at the interface. The solution is given for two types of DCB; one with prescribed rotations (with steady-state crack propagation) and one with prescribed dis...

We study a double-cantilever beam (DCB), in which either the crack-mouth opening displacement or the end rotations are prescribed, in the linear-elastic-fracture-mechanics (LEFM) limit of an infinitely stiff and brittle interface. We present a novel, yet extremely simple, derivation of the closed-form solution of this problem when the arms are mode...

In this work we focus on the mode-I quasi-static crack propagation in adhesive joints or composite laminates. For this problems a number of different standards have been approved. The most widely used are based on the double cantilever beam (DCB) test and on linear elastic fracture mechanics (LEFM) but differ in some aspects of the testing procedur...

In this work we focus on the mode-I quasi-static crack propagation in adhesive joints or composite laminates. For this problems a number of different standards have been approved. The most widely used are based on the double cantilever beam (DCB) test and on linear elastic fracture mechanics (LEFM) but differ in some aspects of the testing procedur...

In this work we focus on the mode-I quasi-static crack propagation in adhesive joints or composite laminates. For this problems a number of different standards have been approved [1]. The most widely used are based on the double cantilever beam (DCB) test and on linear elastic fracture mechanics (LEFM) but differ in some aspects of the testing proc...

Rate dependence of crack propagation is important in many cases of great interest for engineering applications. A rate-dependent cohesive-zone model (CZM) which well captures rate-dependent crack growth along rubber interfaces has been developed in the framework of fractional-calculus based viscoelasticity [1]. Postulating the existence of a rate-i...

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This chapter investigates the so-called "plastic buckling paradox," which states that the deformation theory of plasticity tends to provide values of the buckling loads which are in better agreement with experimental results than those given by the flow theory of plasticity. The paradox lies in the fact that the latter is physically more sound beca...

Experimental tests of multi-pass lined pipe welding are reported and a computational procedure for the determination of the history of temperature, strains and residual stresses is presented in this paper and validated against the experimental test results. The effect of the manufacturing process of the lined pipe on the thermo-mechanical analysis...

We focus on the mode-I quasi-static crack propagation in adhesive joints or composite laminates, where inelastic behaviour is due to damage on a relatively thin interface that can be effectively modelled with a cohesive-zone model (CZM). We studied the difference between the critical energy release rate, Gc , introduced in linear elastic fracture m...

An experimental and numerical investigation on the mechanical response of a lined pipe (compound pipe) under a dynamic impact is presented. The influence of the impact energy has been studied in terms of the depth of the dent formed, and of the strains and residual stresses. To this end, a three-dimensional explicit dynamic non-linear finite elemen...

This paper presents the latest advances in the development of multiplane cohesive-zone models that are able to account for damage, friction and interlocking, including in particular their extension to a general three-dimensional (3D) case. Starting from the work proposed in a recent article by some of the authors, a simplified micromechanical formu...

This paper investigates numerical thermal fields and residual stresses induced by single-pass weld overlay (lap-weld) and girth welding (butt-weld) in lined pipe using Tungsten Inert Gas (TIG) welding. A distributed power density of the moving heat source based on Goldak’s ellipsoid heat flux distribution is used in a Finite Element (FE) simulation...

Welded lined cylindrical structures such as boilers, pressure vessels and transportation pipes are widely used in the oil and gas industries because an inexpensive outer layer is protected from corrosion by a thinner expensive layer, which is made of a corrosion resistant alloy (CRA). Welding in the lined pipe is of two different types, where the f...

Layered structures are widely used in different engineering applications as well as in nature due to their optimised functional and structural performance. Delamination, which occurs when a crack initiates and/or propagates along the interface between two layers, is one of the most prevalent and severe failure modes in these types of structures. In...

Multi-plane Cohesive-Zone Models (M-CZMs), based on the concept of Representative Multiplane Element (RME), provide an intermediate option between macroscale CZMs and full multiscale approaches for the analysis, within the mechanics of generalized continua, of mixed-mode fracture over micro-structured interfaces where initiation and propagation is...

Experimental tests and detailed finite element analyses were carried out on a model of flexible riser to evaluate the capability of the finite element method to predict its nonlinear structural response. The riser consists of four layers, which include two cylindrical polycarbonate tubes and two steel helical layers. One helical layer represents th...

Three–dimensional nonlinear finite–element models have been developed to investigate the loading–unloading–reloading behaviour of two reinforced–concrete beams under four–point bending using explicit dynamics in ABAQUS. The damaged–plasticity model proposed by Lubliner and collaborators was employed for the plain concrete, and elastic–perfectly pla...

The paper presents a nonlinear heat-transfer and mechanical finite-element (FE) analyses of a two-pass welding process of two segments of lined pipe made of a SUS304 stainless steel liner and a C-Mn steel pipe. The two passes consist of the single-pass overlay welding (inner lap weld) of the liner with the C-Mn steel pipe for each segment and the s...

Slojeviti kompozitni nosači imaju široku primjenu u raznim granama industrije i inženjertsva, ali se također i često susreću u prirodi. Karakteristični način sloma takvih nosača najčešće je delaminacija ili raslojavanje. Iako se često delaminacija može proučavati koristeći relativno jednostavne principe linearno-elastične mehanike loma u sprezi s E...

Delamination is one of the one most important problems for layered structures, which are widely used in industry (e.g. composite laminates) and also often present in nature (e.g. layered biological tissue). In this work delamination is studied using cohesive-zone models (CZMs) where a discontinuous displacement field and a non-linear traction-separ...

The present work describes a number of cohesive zone models (CZMs) developed over the last decade; the models are derived from a simplified approach to the micro-mechanics of the fracture process. The models are able to separately consider damage and frictional dissipation; moreover, the most recent proposed models account also for intelocking and...

The paper investigates the elastoplastic buckling of thin circular shells subjected to nonproportional loading consisting of axial tensile stress and external pressure. The governing equations of buckling for cylindrical shells derived by Flugge serve as the basis of analysis. To capture the elastic/plastic behavior, two plasticity theories are con...

This paper presents a highly efficient small-scale, detailed finite-element modelling method for flexible risers which can be effectively implemented in a fully-nested (FE2) multiscale analysis based on computational homogenisation. By exploiting cyclic symmetry and applying periodic boundary conditions, only a small fraction of a flexible pipe is...

In this paper the implementation of two types of boundaries, periodic and fixed in-plane boundaries, for a detailed finite-element model of flexible risers is discussed. By using three-dimensional elements, all layer components are individually modelled and a surface-to-surface frictional contact model is used to simulate their interaction. The app...

This paper presents an analytical model for the study of 2D linear-elastic non-prismatic beams. Its principal aim is to accurately predict both displacements and stresses using a simple procedure and few unknown variables. The approach adopted for the model derivation is the so-called dimensional reduction starting from the Hellinger–Reissner funct...

Many authors in the literature agreed that the flow theory of plasticity either fails to predict buckling or overestimates plastic buckling stresses and strains of plates and shells while the deformation theory succeeds in forecasting buckling and provides estimates that are more in line with the experimental results. Following a previous study by...

This paper presents a numerical investigation on the flexural behaviour of reinforced concrete beams under four-point bending. Three-dimensional nonlinear finite-elements models were developed using ABAQUS/Explicit. The 'Concrete Damaged Plasticity' model was used to model the concrete behaviour. Two different types of elements and meshes were empl...

A three-dimensional (3D) two-scale Cohesive Zone Model (CZM), which is based on a multiplane approach and couples damage with friction and interlocking, is presented for analyzing crack propagation in quasi-brittle materials along structural surfaces where formation of cracks is expected. The main idea of the 3D multiplane formulation herein exploi...

This paper presents the latest advances in the development of cohesive-zone models that are able to account for damage, friction and interlocking, including in particular their extension to a general three-dimensional (3D) case. Starting from the work proposed in a recent article by some of the authors, a simplified micromechanical formulation is u...

A large number of authors in the past have concluded that the flow theory of plasticity tends to overestimate significantly the buckling load for many problems of plates and shells in the plastic range, while the deformation theory generally provides much more accurate predictions and is consequently used in practical applications. Following previo...

Flexible risers which are used for transporting oil and gas between the seabed and surface in ultra-deep waters have a very complex internal structure. Therefore, accurate modeling of their behaviour is a great challenge for the oil and gas industry. Constitutive laws based on beam models which allow the large-scale dynamics of pipes to be related...

Unbonded flexible risers have become the main means of extracting hydro carbonates from deep waters. So, understanding the complex structural integrity of flexible risers has become a crucial issue for the offshore industry. In this paper, an experimental test and a detailed finite element analyses were carried out on a scaled down model of a flexi...

Cohesive-zone models have been widely used for the analysis of interface debonding. In this paper, three of these models are used to study a set of debonding problems. A comparative analysis of the three models is carried out; results are presented and discussed for numerical simulations referring to both single-mode and mixed-mode situations. The...

The present paper deals with the derivation of an interface model characterized by macroscopic fracture energies which are different in modes I and II, the macroscopic fracture energy being the total energy dissipated per unit of fracture area. It is first shown that thermo-dynamical consistency for a model governed by a single damage variable, com...

A numerical analysis of thermal phenomena occurring during lined-pipe welding is presented in this paper. Numerical models of surfaces and volumetric heat sources were used to predict the time evolution of the temperature field both in a corrosion-resistance-alloy (CRA) liner, made of SUS304 stainless steel (SS), and for the single-pass girth weldi...

A recently proposed cohesive-zone model which effectively combines damage, friction and mechanical interlocking has been revisited and further validated by numerically simulating the pull-out test, from a concrete block, of a ribbed steel bar in the post-yield deformation range. The simulated response is in good agreement with experimental measurem...

The structural behavior of precast concrete segmental bridges largely depends on the behavior of the joints between segments. The current practice of precast concrete segmental bridges is to use small keys that are usually unreinforced, normally dry, and distributed over the height of the web and the flange of concrete segments. In this study, a nu...

The paper describes a new non-linear finite-element formulation to analyse fatigue debonding or delamination, along predefined interfaces, which is multi-scale in time. At the small timescale level, cyclic loading and the related oscillating response are considered in an explicit way, whereas at the large timescale level, both the real loading acti...

A recently proposed cohesive-zone model which effectively combines damage, friction and mechanical interlocking has been revisited and further validated by numerically simulating the pull-out test, from a concrete block, of a ribbed steel bar in the post-yield deformation range. The simulated response is in good agreement with experimental measurem...

It has been long known that finding a thoroughly good agreement with experimental results for the buckling loads of circular cylinders in the plastic range constitutes a very difficult task, beyond the same as well challenging problem in the elastic range. This paper attempts to contribute to the understanding of this issue by discussing a few nume...

We present an extension of the computational homogenization theory to cases where different structural models are used at different scales and no energy potential can be defined at the small scale. We observe that volumetric averaging, which is not applicable in such cases unless similarities exist in the macro-scale and micro-scale models, is not...

Detailed stress analysis of unbonded flexible pipes has always been a challenging exercise which requires significant amount of computational resources and state of the art knowledge of flexible pipe modelling techniques. Lloyd’s Register EMEA and Brunel University have embarked on the development of a model which captures the response of the indiv...

Lifespan assessment of flexible risers involves the evaluation of fatigue parameters, requiring accurate predictions of stresses and their variation in pipe components. For predicting the effect of complex three-dimensional nonlinear dynamics on component stress histories, multi-scale methods can combine generality of application with computational...

An experimental investigation has been conducted with the aim to investigate on the midspan debonding failure of reinforced concrete (RC) beams retrofitted in flexure by means of the application of a fiber-reinforced polymer (FRP) lamina externally applied to concrete substratum. Experimental tests on a series of RC beams with different geometries...

A thermodynamics-based cohesive-zone interface formulation combining adhesion, friction and interlocking is illustrated. Interlocking is modeled exploiting a macroscopic description, which represents the geometry of the interface in the form of a periodic arrangement of distinct microplanes, denoted by Representative Interface Element (RIE). The in...

The purpose of this paper is to model the detailed effects of interactions that take place between components of un-bonded flexible risers, and to study the three-dimensional motion responses of risers when subjected to axial loads, bending moments, and internal and external pressures. A constitutive law for un-bonded flexible risers is proposed an...

A multi-scale framework for the analysis of flexible pipes and risers is presented, consisting of (1) a new corotational, elastoplastic beam element for flexible pipe modelling, (2) a representative volume element (RVE) consisting of a detailed shell-element model with interlaminar friction, and (3) a scale-linking scheme for a multiscale analysis...

Two-dimensional nonlinear finite-element analyses of reinforced concrete (RC) beams retrofitted with fiber reinforced polymers (FRP) have been carried out up to failure in order to correctly model the interaction between FRP and concrete substrate, which in general can influence the overall performance of a standard RC element. In order to model th...

This paper presents an analytical formulation and a finite element analysis of the behavior of multilayer unbonded flexible risers. The finite element model accurately incorporates all the fine details of the riser that were previously considered to be important but too difficult to simulate due to the significant associated computational cost. All...

In this paper a new constitutive model for flexible risers is proposed and a procedure for the identification of the related input parameters is developed using a multi-scale approach. The constitutive model is formulated in the framework of an Euler–Bernoulli beam model, with the addition of suitable pressure terms to the generalized stresses to a...

The results of a detailed, non-linear finite-element analysis of a small-scale (i.e. 1.7m long) six-layer unbonded flexible riser, accounting for interlayer contact and frictional slip, are used to calibrate a novel, simplified constitutive model for a 3D, non-linear Euler-Bernoulli beam model suitable for large scale analyses (hundreds of meters i...

We present work in developing and implementing a nonlinear constitutive model that accurately simulates the structural response of unbonded flexible pipes within a modified beam element formulation. This model can be calibrated against detailed finite element simulations, which are impractical for routine large-scale design and analysis, and can pr...

The paper describes a new method to analyse fatigue debonding or delamination, along predefined interfaces, which is multi-scale in time. At the large-scale level both the real loading actions and the related response in terms of displacement field are replaced with their 'minimum' and 'maximum' envelopes over time. The cycle-by-cycle analysis is o...

Recent developments on the numerical analysis of detailed finite element models of unbonded flexible risers using ABAQUS are presented. Several analytical methods are studied and combined together, and their results are compared with those obtained in the finite element model for two different tests, the second one involving cyclic loading. In the...

The gear noise problem that widely occurs in power transmission systems is typically characterised by one or more high amplitude acoustic signals. The noise originates from the vibration of the gear pair system caused by transmission error excitation that arises from tooth profile errors, misalignment and tooth deflections. This paper aims to furth...

The gear noise problem that widely occurs in power transmission systems is typically characterised by one or more high amplitude acoustic signals. The noise originates from the vibration of the gear pair system caused by transmission error excitation that arises from tooth profile errors, misalignment and tooth deflections. This paper aims to furth...

We present a numerical procedure, based upon a tangent approach, for evaluating the ultimate limit state (ULS) of reinforced concrete (RC) sections subject to axial force and biaxial bending. The RC sections are assumed to be of arbitrary polygonal shape and degree of connection; furthermore, it is possible to keep fixed a given amount of the total...

Aim of the work is the study of crack propagation in concrete constructions, such as dams, taking into account the water pressure effects and the damage–friction evolution with unilateral contact. With this aim, an interface model, based on the cohesive fracture, is developed. In particular, a damage–friction model based on a new multiscale approac...

A new method to combine interface damage and friction in a cohesive-zone model is proposed. Starting from the mesomechanical assumption, typically made in a damage-mechanics approach, whereby a representative elementary area of the interface can be additively decomposed into an undamaged and a fully damaged part, the main idea consists of assuming...