Albert Turon

University of Girona | UDG · Department of Mechanic Engineering and Industrial Construction

The main objective of this paper is to present a delamination benchmark test concept for composite materials that develop non-self-similar delamination in characterization specimens. The non-self-similar delamination is induced by rotating the loading blocks. The simplicity of the test allows for analyzing the loading mode history by concatenating...

Impact simulations for damage resistance analysis are computationally intensive due to contact algorithms and advanced damage models. Both methods, which are the main ingredients in an impact event, require refined meshes at the contact zone to obtain accurate predictions of the contact force and damage onset and propagation through the material. T...

Through the application of innovative production processes, thermoplastic composites might help the aviation industry become more sustainable. However, there is currently not much experimental understanding on the fatigue behaviour, and validated analysis methodologies on thermoplastic composites are rather limited. In this work, the fatigue onset...

In this work, a robust method for determining the input fatigue parameters of a fatigue cohesive zone model recently developed by Dávila is presented. The method is based on surrogate modelling and multi objective optimization. Experimental data from delamination tests is used for the parameter determination, highlighting the phenomenological natur...

Impact simulations for damage resistance analysis are computationally intensive due to contact algorithms and advanced damage models. Both methods, which are the main ingredients in an impact event, require refined meshes at the contact zone to obtain accurate predictions of the contact force and damage onset and propagation through the material. T...

Application of advanced composite materials to aircraft primary structures is continuously growing, and projects like Airbus A350XWB in the field of commercial aircrafts or Airbus H160 in the field of civil rotorcrafts are new references of how far composite technology can be implemented. During the last decades, considerable research efforts in th...

The work presented in this paper investigates the ability of continuum damage models to accurately predict matrix failure and ply splitting. Two continuum damage model approaches are implemented that use different stress–strain measures. The first approach is based on small-strain increments and the Cauchy stress, while the second approach account...

A new 3D elastoplastic damage model is proposed to predict the plastic deformation and the progressive failure of unidirectional laminated composite materials at the meso-scale level. A non-associated flow rule is employed to properly define the volumetric plastic strains. The damage evolution laws are defined to account for the failure mechanisms...

Thermoplastic composites can enable the development of new manufacturing techniques to make the aviation industry more sustainable while at the same time greatly benefit cost-efficient and high-volume production. One of the thermoplastic composite materials that can enable this transition is AS4/PEKK-FC. In this work, the interlaminar properties of...

This paper investigates the effect of environmental conditions on the cohesive law of composite bonded joints under mode I and mode II loadings. An inverse method recently developed by the authors has been used to extract the cohesive stress-separation relation from the experimental load–displacement curve without considering a predefined shape of...

The capability of joining two thermoplastic composite parts by welding is a key technology to reduce the weight and cost of assembled parts and enables high volume manufacturing of future aeronautical structures made of thermoplastic composite materials. However, there is not much experimental understanding of the mechanisms involving welded joint...

We performed in-situ tensile tests on two carbon fibre/epoxy composites with continuous scanning using synchrotron computed tomography (CT). Both composites were cross-ply laminates, and two specimens were tested for each composite. The voxel size was sufficiently small to recognize individual fibres and fibre breaks. For each test, 16-19 volumes w...

Longitudinal tensile failure of unidirectional fibre-reinforced composites remains difficult to predict accurately. The key underlying mechanism is the tensile failure of individual fibres. This paper objectively measured the relevant input data and performed a detailed experimental validation of blind predictions of six state-of-the-art models usi...

The effect of environmental conditions on the fracture behaviour of two types of adhesively bonded joints (wet-aged and non-aged) is experimentally studied under mode II loading. End Loaded Split tests were performed at various temperatures (-55°C, room temperature (RT) and 80°C) on non-aged and aged specimens. The non-aged specimens were stored in...

While fibre hybrid composites result in hybrid effects and improved ductility compared to non-hybrid laminates, it is unclear how material size influences hybrid properties (i.e. the so-called ‘size effect’). This paper addresses this phenomenon in a carbon–carbon hybrid composite by means of micromechanical modelling using a progressive failure mo...

Mesoscale modelling of delamination has been extensively addressed in the literature. Actually, most common nonlinear finite element codes incorporate different technologies to predict delamination. These technologies are either based on the direct application of fracture mechanics or using the cohesive zone model concept. In this chapter, both app...

This paper follows on from part III (Llobet et al., 2020) where a mesoscale continuum damage mechanics (CDM) model for composite laminates under static and fatigue loads has been presented. An experimental investigation on the damage occurrence and the strength of carbon/epoxy notched laminates subjected to static, tension-tension fatigue and resid...

Many models for prediction of longitudinal tensile failure of unidirectional (UD) composites have been developed in the last decades. These models require significant assumptions and simplifications, but their consequences for the predictions are often not clearly understood. This paper therefore presents a blind benchmark of seven different models...

The influence of different harsh environmental conditions on the fracture behaviour of secondary bonded adhesive joints is experimentally investigated using mode I DCB tests. Two types of adhesively bonded joints under wet-aged and non-aged conditions were tested at three temperatures: −55 °C, room temperature and 80 °C. The wet-aged specimens were...

Aeronautical industries address the structural reliability of designs by defining design allowables that account for any uncertainties. The Composite Materials Handbook-17 proposes A/B-basis values as design allowables. In this study, a new methodology to estimate the design allowables of the Compression After Impact (CAI) strength is presented. Th...

The resistance to fracture of a bonded joint is usually evaluated through the experimental characterisation of its fracture toughness. Different test procedures and data reduction methods are available in the literature, such as the ISO-25217 test standard. The need for crack length measurement has led to inaccurate results when large adhesive thic...

In the quest to improve the compression after impact (CAI) strength of thin laminates, ply-hybrid laminates (where plies of different thicknesses are mixed) have been used in a previous study to mitigate the fibre failure and, consequently, improve the CAI strength. In the same study, hybrid laminates were proposed following qualitative design rule...

Transverse intralaminar cracks in layers with perpendicular orientation referred to the main loading direction have a significant affection on the apparent ultimate strength of the corresponding composite laminate. This effect stems from the fact that such transverse cracks generally promote the occurrence of other failure mechanisms leading to the...

The progressive damage analysis of fiber-reinforced composite materials is a challenging task, especially when complicated cracking scenarios arise due to the onset and progression of several damage mechanisms. From a modeling point of view, a particularly complex failure scenario is the interaction between intralaminar and interlaminar cracks. Thi...

The usual way to evaluate the fracture toughness of bonded joints is via experimental characterization of the critical strain energy release rate. Different test procedures and data reduction methods for mode I fracture characterization can be found in the literature, such as ISO-25217, where crack length measurement is required. However, obtaining...

This paper aims to discuss the effect mode II type tests have on the cohesive law of bonded joints. For this reason, an objective inverse method has been developed to extract the cohesive law for experimental load-displacement data using an analytical procedure to represent the fracture process zone of mode II tests. The method is implemented on th...

A progressive failure model including dynamic effects and thermal residual stresses able to simulate the failure and damage development of hybrid unidirectional polymer composites under fibre tensile loading is presented. The model is used to study the influence dynamic effects and thermal residual stresses have on the development of clusters of fi...

Cohesive Zone Models (CZM) are widely used for modeling bonded joints. The main difficulty concerning the use of CZM is the obtention of the interface cohesive law. To measure the cohesive law of bonded joints, experimental methods have been developed which are tedious and expensive because they require the use of additional measurement techniques...

Most of the existing methods for fatigue-driven delamination are limited to two-dimensional (2D) applications or their predictive capabilities have not been validated in three-dimensional (3D) problems. This work presents a new cohesive zone-based computational method for simulating fatigue-driven delamination in the analysis of 3D structures witho...

The stiffness and strength of a bonded joint mainly depend on the geometry of the assembly and the constitutive behaviour of its constituent parts (adherends, adhesives and interfaces). The adhesive itself may sustain a significant hydrostatic contribution to fluctuation along the bonded area, strongly influencing the local joint stiffness and stre...

Most of the existing methods for fatigue-driven delamination are limited to two-dimensional (2D) applications or their predictive capabilities have not been validated in three-dimensional (3D) problems. This work presents a new cohesive zone-based computational method for simulating fatigue-driven delamination in the analysis of 3D structures witho...

Computing mode-decomposed energy release rates in arbitrarily shaped delaminations involving large fracture process zones has not been previously investigated. The J -integral is a suitable method for calculating this, because its domain-independence can be employed to reduce the integration domain to a cohesive interface, and reduce it to a line i...

A spring element model that takes into account the dynamic effects associated with fibre failure in composite materials is presented. The model is implemented in a parallel environment to allow a better performance in the prediction of the complex mechanisms associated with longitudinal tensile failure. The model is used to identify the changes in...

This data repository provides the processed data obtained from the benchmark simulation using the method presented in the article entitled "A simulation method for fatigue-driven delamination in layered structures involving non-negligible fracture process zones and arbitrarily shaped crack fronts" by the same authors. The method is based on a cohes...

A cyclic cohesive zone model is developed which is capable of predicting fatigue driven delamination under thermo–mechanical loading conditions. The model is an extension of an exponential traction–separation law describing the quasi–static constitutive behavior of the interface. Mixed–mode loading conditions are accounted for using an interaction...

Models for simulating interlaminar crack growth in composites under static and fatigue loads are rarely validated with experimental data different from simple standard tests where the crack front propagates with a uniform shape. The underlying reason for not making use of more realistic experimental data, where the crack front shape changes during...

The development of predictive numerical methods, which accurately represent the progressive failure of long fiber composite materials, is nowadays required for the achievement of optimized mechanical responses in terms of load bearing capacities of modern composite structures. In this investigation, two characteristic failure mechanisms of long fib...

A new numerically-based method suitable for determining the total strain energy release rate (SERR) involved in two-dimensional (2D) Mode I-dominated delamination under opening loads in FRP laminates is presented. The method is based on the mutual dependence of the load vs opening displacement curves slope exhibited after the full development of th...

This paper presents an analytical model to predict the stress redistribution around broken fibres in hybrid polymer composites. The model is used under the framework of a progressive failure approach to study the load redistribution around breaks in hybrid composites. The outcomes of the model are validated by comparing it with a spring element mod...

The design of composite structures relies on the accurate determination of design allowables, which are statistically based material parameters that take into account manufacturing, geometrical and microstructure variability. The accurate determination of these design parameters requires extensive experimental testing, which makes the certification...

Thin-ply composite laminates are currently receiving researchers’ attention due to their specific advantages in delaying or even suppressing some damage mechanisms such as matrix cracks. Lower load capacity during impact event is one of the main factors against thin-ply laminates use. This paper presents novel thin-ply laminate design with improved...

This data repository provides the processed data to reproduce the findings presented in the article entitled "A benchmark test for validating 3D simulation methods for delamination growth under quasi-static and fatigue loading" by the same authors. In this work, a comprehensive benchmark case consisting of a double cantilever beam (DCB)-like specim...

An in-depth analysis of the stress fields that surround a broken fibre in fibre reinforced composites is performed and the effects of different material properties are analysed. The stress fields obtained using a spring element model with a random distribution are compared with analytical formulations present in the literature, within a progressive...

This work presents a novel procedure to characterize the crack growth rate curve under fatigue mixed mode I + II loading conditions with only one specimen. The procedure is based on applying a variable cyclic displacement during a Mixed Mode Bending (MMB) test together with a real time monitoring of the specimen’s compliance. The method introduces...

The identification of the delamination propagation direction in three-dimensional structures with arbitrarily shaped fronts is needed in many applications. In the cohesive element framework, the propagation direction may be computed as the normal direction to a numerical damage isoline. The damage isoline tracking requires to exchange information b...

A numerical investigation was carried out in order to simulate experimental results previously obtained concerning two-dimensional (2D) in-plane crack propagation in laminated glass fiber-reinforced polymer (GFRP) plates. The laminated plates were designed with an embedded circular pre-crack and subjected to quasi-static out-of-plane loads. In orde...

A 3D constitutive damage model is proposed for predicting the progressive failure of laminated composite materials at mesoscopic length scale. The damage initiation and growth functions are based on the experimental phenomenology. The damage evolution laws are defined ensuring the energy regularization thanks to the crack band model. The crack clos...

This paper presents a three-dimensional Progressive Failure Model based on the chain of bundles able to represent the stiffness loss in unidirectional composite materials loaded in the fibre direction. A representative volume element with a random distribution of fibres with their own radius is considered. Complete stress distributions around fibre...

This chapter describes the main topics related to the use of cohesive elements in the simulation of delamination in polymer composite materials. The kinematic and constitutive idealizations used in cohesive zone models, as well as the numerical implementation of cohesive zone models in the context of the finite element methods is discussed. Guideli...

An efficient computational model to simulate tensile failure of both hybrid and non-hybrid composite materials is proposed. This model is based on the spring element model, which is extended to a random 2D fibre packing. The proposed model is used to study the local stress fields around a broken fibre as well as the failure process in composite mat...

While analytical fiber fragmentation models following the global load-sharing (GLS) assumption efficiently reproduce the stress strain curves of unidirectional composites loaded in the direction of the reinforcement when the number of breaks is moderate, they completely fail to predict tensile strength. In this paper, we propose that failure takes...

The cohesive zone model approach in conjunction with a damage formulation, has been used by many authors to simulate delamination using finite element codes. However, some models available in the literature have not been validated correctly under mixed-mode loading conditions. An incorrect selection of the parameters of the model can result in inac...

A Cyclic Cohesive Zone Model is developed which is an extension of an exponential traction–separation law describing the quasi–static constitutive behavior of the interface. Damage degradation under fatigue loading is accounted in a cycle–by–cycle analysis. A Paris’ law type formulation is utilized to model fatigue damage which is based on physical...

A new analytical model to predict progressive failure in a double cantilever beam (DCB) bonded joint is proposed. The model is based on the Winkler elastic foundation theory and coupled with a damage model based on the cohesive zone approach. The elastic behaviour of the adhesive layer is accounted for defining a new general stiffness foundation fu...

The analysis of damage progression in Non-Crimp-Fabric (NCF) composite laminates subjected to out-of-plane loading is complicated due to the number of damage mechanisms and the involved sequence, but it is even more complex when the plies are thin. Damage development results from the interaction of different failure mechanisms such as matrix cracki...

New benchmark studies of six different computational methods for simulating fatigue-driven delamination cracks in composite laminated structures under cyclic loading are presented. All the studied methods are based on cohesive zone models and are aimed at high-cycle fatigue simulation. The benchmark studies describe and compare the traction-separat...

Crack growth rate curves provide information about the delamination resistance of composite materials under cyclic loading. The existing methodologies for mode II fatigue testing using three-point bending end-notched flexure (3-ENF) under constant cyclic displacement conditions yield discontinuous delamination growth rate curves, therefore requirin...

Modeling adhesive joints by means of cohesive models relies on the definition of cohesive laws. Although cohesive laws are known to be dependent on the loading mode, there is a lack of experimental evidences to describe this dependence. At the same time, the adherend and adhesive thicknesses are known to affect the fracture toughness of the bond, b...

A new general analytical model based on elastic foundation beam theory is proposed for adhesively bonded double cantilever beam (DCB) specimens. The new model accounts for any stress state (from plane stress to plane strain) in the adhesive and therefore, the model is able to predict the mechanical response of a DCB specimens whatever the adhesive...

The use of recycled aggregate concrete (RAC) contributes to reducing energy and natural resource consumption in the construction industry. However, incorporating recycled concrete aggregates (RCA) into the concrete production process usually causes some difficulties in controlling fresh and hardened concrete properties. One of the properties suscep...

Three different models with increased complexity to study the effects of hybridization on the tensile failure of hybrid composites are proposed. The first model is a model for dry bundles of fibres based on the statistics of fibre strength. The second is a model for composite materials based on the multiple fragmentation phenomenon. Lastly, a micro...

A new cohesive element formulation is proposed for modeling the initial elastic response, softening, and failure of finite-thickness adhesives. By decoupling the penalty stiffness of the cohesive zone model formulation and the physical adhesive modulus, the new formulation ensures proper dissipation of fracture energy for opening and shear loading...

Polymer-based laminated composite materials can fail by delamination. Cohesive zone development occurs during delamination, where dissipation mechanisms take place. Within a numerical framework, a fine discretization is needed along the cohesive zone length to accurately capture the non-linear stress distribution. Knowing the cohesive zone length b...

Delaminations at the free-edges of a laminated composite under tension can be triggered by transverse cracks or by high interlaminar stresses. The capability for predicting these phenomena when the ply thickness is reduced (thin-ply laminates) is particularly challenging because damage mechanisms are delayed or even suppressed. In this work, an exi...

This chapter discusses the methodologies used to analyse fatigue-induced damage of bonded joints between composite components under mode I cyclic loads. It first reviews the existing types of bonded joints used in manufacturing or repair procedures. Then, the chapter presents some general considerations related to mode I testing of adhesive joints,...

This chapter presents the formulation for an extension of quasi-static cohesive zone models to simulate fatigue-driven delaminations. The basis for the fatigue formulation is to link the evolution of the damage variable to the crack growth rate da/dN that can be measured in experiments. The model relates damage accumulation to the number of load cy...

The analysis of large-scale fracture processes, such as those involved in the fracture of adhesive joints, falls outside the scope of Linear Elastic Fracture Mechanics (LEFM). However, experimental data produced in testing adhesive joints are usually reduced with LEFM methods. The consequent error has not yet been evaluated. In this work, an experi...

Flexible adhesive joints, with adhesives of very low elastic modulus and very large failure deformation, are of special interest in industrial applications. Nevertheless, there is a lack of effective models for predicting their behaviour for structural applications. Existing methods developed for stiff compressible adhesives are not able to accurat...