Vladislav Mantič

Universidad de Sevilla | US · School of Engineering, Department of Continuum Mechanics and Theory of Structures

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...

Abstract: A numerical procedure predicting crack onset and growth in brittle materials is developed using the Coupled Criterion of Finite Fracture Mechanics (CCFFM) [1] which assumes crack advances by finite steps and requires both stress and energy conditions are fulfilled. Crack advances are bridged by a continuous distribution of springs, simila...

Durante la realización de ensayos de fatiga a tracción en laminados cross-ply con láminas ultradelgadas, se han observado fallos poco convencionales antes o durante los primeros ciclos de carga. Dichos fallos consisten en la aparición de despegues longitudinales (paralelos a la dirección longitudinal de las fibras de las capas de 0º) en la capa de...

In the present work the Coupled Criterion of Finite Fracture Mechanics (CCFFM) is used to predict crack onset or growth by finite increments on a linear elastic interface. The predictions of the interface failure by two alternative approaches of the CCFFM applied to the Linear Elastic Brittle Interface Model (LEBIM): the widely used method based on...

A computational code based on a semianalytic procedure for the determination of the characteristic exponents and the singular stress and displacement fields in multi-material corners is developed. Linear elastic anisotropic materials under generalized plane strain state are considered. This code is a universal computational tool able to analyse bot...

Problems of stress singularities in single or multi-material corners have been addressed by many authors over the years. Most of the authors presented closed-form corner-eigenequations for special cases, and often there is no easy way to check if the solution is correct. In this work, we present a general computational tool that can solve many diff...

A comparison of the interface fracture energy in the adhesive joints PMMA/PMMA bonded by epoxy and PMMA/epoxy is presented. The work focuses on the question of how similar is the fracture energy in these joints, including its dependence on the fracture mode mixity. Series of tests for Brazilian disk specimens subjected to compressive loading were c...

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This paper explores the possibility of using the Gurtin-Murdoch theory of material surface for modeling mechanical processes in nanomaterials reinforced by two-dimensional flexible and extensible nanoplatelets. In accordance with the theory, reinforcement is modeled by a vanishing thickness prestressed membrane embedded in an isotropic elastic matr...

Crack onset in PMMA holed plates subjected to tensile stresses is studied experimentally and by the coupled stress and energy criterion of the Finite Fracture Mechanics (CCFFM). The elastic, strength and fracture properties of PMMA are determined by the standard tests, a clearly nonlinear stress-strain relation being identified in the tensile tests...

A new analytical solution in the form of asymptotic series is proposed and studied for Mode III crack problems with spring boundary conditions, which are, in the mathematically-oriented literature, referred to as Robin boundary conditions. Under the assumption of antiplane shear loading, the corresponding elastic problem reduces to the Laplace equa...

The prediction of failure mechanisms in fibre-reinforced composite materials is of great importance for the design of composite engineering applications. With the aim of providing a tool able to predict and explain the initiation and propagation of damage in unidirectional fiber reinforced composites, in this contribution we develop a micromechanic...

The phenomenon of arrest of an unstably-growing crack due to a curved weak interface is investigated. The weak interface can produce the deviation of the crack path, trapping the crack at the interface, leading to stable crack growth for certain interface geometries. This idea could be used as a technical solution for a new type of crack arrester,...

The antiplane problem of an infinite isotropic elastic medium subjected to a far-field load and containing a zero thickness layer of arbitrary shape described by the Gurtin-Murdoch model is considered. It is shown that, under the antiplane assumptions, the governing equations of the complete Gurtin-Murdoch model are inconsistent for non-zero surfac...

A new analytical procedure is developed for the deduction of the asymptotic series of the singular solutions in displacements and stresses near the vertex of the linear elastic isotropic corners with the Dirichlet–Robin (fixed-spring) and Neumann–Robin (free-spring) boundary conditions. Under the assumption of antiplane shear loading, the correspon...

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...

This work presents three examples of standard test configurations, involving composite materials, where the presence of stress singularities induced by adhesive joints causes premature failures leading to underestimated strength values. Slight modifications of the local geometry, removing or reducing, in these critical points, the order of the stre...

The phenomenon of arrest of an unstably-growing crack due to a curved weak interface is investigated. The weak interface can produce the deviation of the crack path, trapping the crack at the interface, leading to stable crack growth for certain interface geometries. This evidence could be exploited as a technical solution for a new type of crack a...

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...

This work studies how the direction of crack propagation affects the translaminar fracture toughness in composites. In particular, this work focuses on propagation mode-I toughness. The two extreme cases are analyzed: crack propagating in the direction either parallel or perpendicular to the fibers (always without breaking fibers). To evaluate the...

Even well-established non-linear FEM codes may present convergence issues when solving highly unstable problems, e.g. fracture mechanics problems, especially in the presence of a pronounced snap-back behaviour. In composites, at lamina level, the debonds occurring between the fibres and matrix, lead to multiple-crack configurations. Each individual...

Interface models for triggering damage events have been extensively used in many engineering applications due to their inherent versatility and relatively simple numerical implementations. Usually, the non-linear behavior of interfaces and thin adhesive joints between solids has been modeled using Cohesive Zone Models (CZMs) although other alternat...

A unified methodology to solve problems of frictionless unilateral contact as well as adhesive contact between linear elastic solids is presented. This methodology is based on energetic principles and is casted to a minimization problem of the total potential energy. Appropriate boundary integral forms of the energy are defined and the quadratic pr...

Transverse cracking of off-axis plies is typically the first step of some failure mechanisms in long fiber reinforced laminated composites. It is well known that the off-axis ply thickness affects strongly the strain level which this ply is able to withstand without cracking. Experimental evidences show that this critical strain level increases str...

A procedure based on the Linear Elastic Brittle Interface Model (LEBIM) combined with the Coupled Criterion of Finite Fracture Mechanics (CCFFM) is successfully implemented in a 2D Boundary Element Method (BEM) code. In the original LEBIM formulation, the values of the interface strength, fracture toughness and stiffness are dependent on each other...

A model to predict transverse cracking in cross-ply laminates in the presence of residual thermal stresses is developed here. This model is based on the coupled criterion of the finite fracture mechanics. This criterion has been successfully used for different materials, structures and scales to predict crack initiation. It is based on two main hyp...

Transverse cracking, i.e. matrix cracking in the off-axis plies of the laminate, is widely recognized as the first damage mode to appear in continuous fibre-reinforced composite laminates subjected to in-plane loading. Since transverse cracking has a great influence on the subsequent damage steps such as delaminations or oblique cracks, it is impor...

One of the reasons for the application of composites to mobile structures is their capacity to absorb energy under impact. As their components have a very reduced interval of deformation till breakage, the mechanism of absorption of energy cannot be based on plasticity but on the capacity of generating free surfaces inside the material, the debondi...

A recently proposed criterion is used to study the behavior of debonds produced at a fiber–matrix interface. The criterion is based on the Linear Elastic–(Perfectly) Brittle Interface Model (LEBIM) combined with a Finite Fracture Mechanics (FFM) approach, where the stress and energy criteria are suitably coupled. Special attention is given to the d...

Micromechanics has been widely used in the link in between an actual non-homogeneous composite ply involving fibre and matrix and an equivalent homogeneous ply with non-isotropic behaviour, connecting stiffness and strength properties of the equivalent lamina with the properties of fibre and matrix. The authors believe that beyond this, Micromechan...

A Galerkin boundary integral formulation for 3D axisymmetric Stokes flow is presented. The singular integrals are evaluated by splitting the complicated Green’s function kernels into a singular term that can be integrated analytically, plus a term for which Gauss quadrature provides sufficient accuracy. As in a previous axisymmetric Laplace impleme...

Onset and growth of debonds at fibre–matrix interfaces in a bundle of fibres subjected to transverse loads are studied numerically. In particular, the crack path formed by debonded neighbour fibres is analysed. The Linear Elastic–Brittle Interface Model (LEBIM) is used to model the fibre–matrix interface behaviour. This simple model of a Long Fibre...

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...

A new quasi-static and energy based formulation of an interface damage model which provides interface traction-relative displacement laws like in traditional trilinear (with bilinear softening) or generally multilinear cohesive zone models frequently used by engineers is presented. This cohesive type response of the interface may represent the beha...

Macro-scale delamination and micro-scale fibre-matrix debonding events may notably affect the mechanical performance of fibrous composite elements. This paper presents a 2D Finite Element (FE)-based formulation of interface of a small but finite thickness relying on the so-called Linear Elastic-Brittle Interface Model (LEBIM) to be applied for simu...

This chapter reviews mathematical approaches to inelastic processes on the surfaces of elastic bodies. We mostly consider a quasistatic and rate-independent evolution at small strains. Various concepts of solutions are introduced and applied (including their comparison), e.g., to elastic-brittle delamination, cohesive contact problems, and to delam...

The objective of this chapter is the study of the interfiber–matrix failure under tension. The initial micromechanical stages of this damage mechanism are identified and studied. The boundary elements method is employed and interfacial fracture mechanics concepts are used for the analysis of the results. Two complementary studies are also presented...

In the present chapter, the failure prediction of composite joints is addressed in the framework of failure induced by the presence of singular stress states at the multi-material corners appearing at the end of the overlap region. A comprehensive description of the singular stress characterization at multi-material corners of composite materials i...

The propagation of fiber–matrix interfacial debonding under axial loading is analyzed, using the single-fiber fragmentation test as a reference, in order to determine fiber–matrix failure properties. A data reduction technique is presented in which the fiber–matrix Mode II interfacial fracture toughness is obtained from the measurements of the aver...

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...

The quasistatic normal-compliance contact problem of isotropic homogeneous linear visco-elastic bodies with Coulomb friction at small strains in Kelvin-Voigt rheology is considered. The discretization is made by a semi-implicit formula in time and the Symmetric Galerkin Boundary Element Method (SGBEM) in space, assuming that the ratio of the viscos...

The first damage mode to appear in continuous fibre-reinforced composite laminates subjected to in-plane loading is usually transverse cracking, i.e. matrix cracking in the off-axis plies of the laminate. Since the density of transverse cracks has a great influence on the subsequent failure steps like delaminations, it is important to be able to pr...

Understanding matrix failure in LFRP composites is one of the main challenges when developing failure criteria for these materials. This work aims to study the influence of the secondary transverse load on the crack initiation at micro-scale. Four non-classical approaches of fracture mechanics are used to model the onset of fibre-matrix interface d...

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...

Transverse cracking in cross-ply laminates is a key failure mechanism which needs to be understood in order to predict the failure initiation in these laminates. A new 2D model has recently been presented (García et al., Int J Solids Struct 51, pp. 3844-3856, 2014) for predicting the first crack onsets in cross-ply laminates under tensile loading,...

A numerical study of the onset and growth of debonds at fibre-matrix interfaces, for a fibre bundle under far field biaxial transverse loads, is presented. The behaviour of the fibre-matrix interface cracks was studied by means of a Linear Elastic-Brittle Interface Model (LEBIM). The simplified, but representative, model of an actual unidirectional...

The contact problem with Coulomb friction together with a simple Kelvin-Voigt viscoelastic model is studied. The numerical solution is obtained using a time discretization by a semi-implicit formula, the visco-elastic solids in contact being discretized by Symmetric Galerkin Boundary Element Method (SGBEM). The resulting minimization problem with a...

The determination of the tensile and shear strengths of homogeneous materials can be easily performed by standard tensile and shear (e.g. Iosipescu) tests. Nevertheless, when the determination of these strengths involves a bimaterial interface, the standard samples present bimaterial corner configurations at their free-edges which generate singular...

In the present work, the coupled stress and energy criterion of Finite Fracture Mechanics (FFM) is applied to investigate negative T-stress effects related to mixed-mode brittle fracture of cracked elements. Only two material parameters are involved in the analysis, the tensile strength and the fracture toughness, which are independent of the mode-...

Two models for quasistatic adhesive unilateral contact delaminating in mixed fracture mode, i.e. distinguishing the less-dissipative Mode I (opening) from the more-dissipative Mode II (shearing), and allowing rigorous mathematical and numerical analysis, are studied. One model, referred to as Associative Plasticity-based Rate-Independent Model (APR...

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...

A new linear elastic and perfectly brittle interface model for mixed mode is presented and analysed. In this model, the interface is represented by a continuous distribution of springs which simulates the presence of a thin elastic layer. The constitutive law for the continuous distribution of normal and tangential initially-linear-elastic springs...

The Conferences on Boundary Element and Meshless Techniques are devoted to fostering the continued involvement of the research community in identifying new problem areas, mathematical procedures, innovative applications, and novel solution techniques in both boundary element methods (BEM) and boundary integral equation methods (BIEM). Previous succ...

Composite to metal adhesively bonded joints generates critical points where geometry and material properties change abruptly. These points (multimaterial corners) are potential locations for failure initiation. There exist proposals predicting the initiation of failure at these multimaterial corners using a Fracture Mechanics approach, in which the...

The quasistatic rate-independent evolution of a delamination at small strains in the so-called mixed mode, i.e.~distinguishing opening (Mode I) from shearing (Mode II) is rigorously analyzed in the context of a concept of stress-driven local solutions. The model has separately convex stored energy and is associative, namely the 1-homogeneous potent...

The controversy about the symmetry of the debond onset at the fibre-matrix interface in single-fibre specimens under transverse tension is studied here applying the coupled stress and energy criterion of the finite fracture mechanics. This criterion enables to compare the two different post-failure configurations found in the literature studying th...

A theoretical model is developed to predict debond onset in spherical-particle-reinforced composites subjected to uniaxial tension. The coupled stress and incremental energy criterion of the finite fracture mechanics is applied employing an axisymmetric boundary element method code, which is highly accurate in the analysis of interface cracks in pr...

The problem of crack initiation at the interface of a spherical inclusion embedded in an infinite matrix subjected to a remote tension is studied by the means of the coupled criterion of the finite fracture mechanics. This allows us to predict the critical tension necessary to initiate the crack at the interface as a function of the elastic propert...

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...

A quasi-static rate-independent model of delamination of linearly elastic bodies at small strains, sensitive to mode of delamination, using interfacial damage and interfacial plasticity as two internal parameters, is further developed with the aim to extract representations typically employed in engineering interface-models, i.e. fracture envelope...

Crack initiation in the inner ply of symmetric [0/90]s[0/90]s laminates under tension is studied applying the coupled stress and energy criterion proposed by Leguillon (Eur. J. Mech. A/Solids 21, 2002) in the framework of the finite fracture mechanics. This criterion assumes that a crack of a finite extension appears abruptly when the stress criter...

The objective of this paper is the study of the inter-fibre/matrix failure under biaxial loading. In particular the influence at micromechanical scale of the presence of a secondary transverse load (tension or compression) perpendicular to the transverse tension nominally responsible for the failure is studied for all phases of the mechanism of dam...

The present study is focused on the fatigue failure initiation at bimaterial corners by means of a configuration based on the Brazilian disc specimens. These specimens were previously used for the generalized fracture toughness determination and prediction of failure in adhesive joints, carried out under static compressive loading. Under static loa...

The present authors and coworkers have recently developed a new physically and mathematically well justified and efficient ap proach for interface crack onset and propagation, implemented in finite and boundary element method (FEM and BEM) codes and applied to several problems of engineering interest. This approach borrows concepts from damage mechan...

Relations between different solutions of an interface crack in a neighborhood of the crack tip given by the open model, frictionless and frictional contact models of interface cracks are analyzed numerically for a penny-shaped interface crack subjected to remote tension. A new analytic expression for the size of the near-tip contact zone in presenc...

A simple, yet efficient procedure to solve quasistatic problems of special linear visco-elastic solids at small strains with equal rheological response in all tensorial components, utilizing boundary element method (BEM), is introduced. This procedure is based on the implicit discretisation in time (the so-called Rothe method) combined with a simpl...

The strength of open-hole composite laminate specimens under tension is studied. In particular, the influence of the stress concentrator size and specimen geometry on the crack onset and consequently on the final open-hole strength is analyzed. A model based on the Finite Fracture Mechanics (FFM) including the coupled stress-energy criterion is app...

The influence of a secondary transverse load (tension or compression), perpendicular to the transverse compression nominally responsible for the failure, on the inter-fibre failure is studied at micromechanical level. The problem is analysed by means of the Boundary Element Method and under the light of Interfacial Fracture Mechanics. The results o...

The instability behaviour associated to a crack onset and propagation along the fibre-matrix interface in a composite system under remote transverse loads is studied by a means of the linear elastic - (perfectly) brittle interface model (LEBIM). LEBIM has proved to model adequately the behaviour of this interface represented by a continuous distrib...

A FEM study of debond onset and growth at fibre-matrix interfaces in a single fibre and in a group of ten fibres subjected to remote transverse load is presented. The debond is modelled using the Linear Elastic Brittle Interface Model (LEBIM) which is implemented in the commercial FEM code Abaqus using a user subroutine UMAT. In both cases studied,...

Computational methods developed to predict crack onset and growth in composites are briefly reviewed first. Assuming crack advances by (possibly) finite steps, which is the basic assumption of Finite Fracture Mechanics (FFM), in opposite to the hypothesis of crack advance by infinitesimal steps adopted in classical Linear Elastic Fracture Mechanics...

Fracture of open hole polymer plates in tension is addressed by the coupled stress-energy criterion of Finite Fracture Mechanics, using Finite Element simulations with different material models. Although the final objective is to understand the behaviour of stretched open hole polymer matrix plates, in the present work, linear elastic and nonlinear...

The fiber-size effects on the value of the homogenized transverse stress leading to the onset of crack initiation at the fiber-matrix interface predicted by the cohesive zone model and by the finite fracture mechanics theory are herein compared and discussed. The results show a good agreement except for the limit cases corresponding to small or ver...

Composite to metal adhesively bonded joints generates critical points where geometry and material properties change abruptly. These points (multimaterial corners) are potential locations for failure initiation. There exist proposals predicting the initiation of failure at these multimaterial corners using a Fracture Mechanics approach, in which the...

A test is developed to compare the transverse fracture toughness of a crack growing along the longitudinal and transverse directions of long-fiber-reinforced laminates. The test proposed is based on a three point bending (TPB) test. The starter crack will be generated inserting a non-adhesive nylon film prior to the curing process. Once the specime...

A new numerical model able to predict interface damage considering Coulomb friction contact between debonded surfaces is developed and implemented. A comparison of two variants of this model is presented from the mathematical and engineering point of view, the linear elastic-brittle interface model anda cohesive interface model, both combined with...

The crack onset and propagation at the fibre-matrix interface in a composite under tensile/compressive remote biaxial transverse loads is studied by a new linear elastic - (perfectly) brittle interface model. In this model the interface is represented by a continuous distribution of springs which simulates the presence of a thin elastic layer. The...

An adhesive unilateral contact of elastic bodies with a small viscosity in the linear Kelvin-Voigt rheology at small strains is scrutinized. The flow-rule for debonding the adhesive is considered rate-independent and unidirectional, and inertia is neglected. The asymptotics for the viscosity approaching zero towards purely elastic material involves...

The quasistatic rate-independent evolution of delamination in the so-called mixed-mode, i.e. distinguishing opening (mode I) from shearing (mode II), devised in [45], is described in detail and rigorously analysed as far as existence of the so-called energetic solutions concerns. The model formulated at small strains uses a delamination parameter o...

The problem of fiber-matrix debonding due to transverse loading is revisited. Predictions of the critical load for the debond onset obtained by a Cohesive Zone Model combined with contact mechanics and by a Finite Fracture Mechanics model based on a coupled stress and energy criterion are compared. Both models predict a strong nonlinear dependence...