Olivier Allix

Interlaminar interface modelling for the prediction of delamination

Abstract Delamination is a phenomenon which involves complex degradations of layers and interlaminar connections. In order to take these degradations into account, a laminate is modelled as a stacking sequence of homogeneous layers and interlaminar interfaces. The aim of this article is to focus on the interface modelling and first identification. The interface is a three-dimensional medium the thickness of which is negligible compared to the in-plane dimensions. Therefore it can be modelled as a two-dimensional entity which ensures displacement and traction transfer from one ply to another. The interface depends on the angle between the fibre directions of two adjacent layers. In the first instance it is assumed to be elastic and damageable. The main interest of this model is that, using only a few intrinsic characteristics of the interface, it is possible to predict the tendency of a structure to delaminate. One of the main difficulties is to identify these characteristics. This approach allows a clear connection between fracture mechanics and damage mechanics. This modelling has been used for the predicting of delamination initiation and growth in the case of static loadings without buckling.

Damage analysis of interlaminar fracture specimens

Abstract Interlaminar fracture specimens are widely used for studying the interlaminar toughness of composite laminates. The goal of this paper is to analyse delamination specimens within the framework of a damage meso-modelling of composite laminates. In this type of modelling a laminate is described as a stacking sequence of homogeneous layers and interlaminar interfaces. The interface is assumed to be damageable in order to model the delamination phenomena. In the case of the propagation of a pre-existing crack, the main parameters for the interface model identification are the critical energy release rates. Delamination specimens are here modelled as two beams connected by a damageable interface. By means of a Finite Element Scheme used in connection with a Riks-like algorithm, comparisons between numerical simulation and experiments have been performed for a wide class of specimens (D.C.B., E.N.F., E.L.S.). The results show the interest of the proposed modelling, which allows a complete simulation of delamination using of relatively little experimental data.

Modeling and simulation of crack propagation in mixed-modes interlaminar fracture specimens

A study of mixed-mode crack propagation in bending-based interlaminar fracture specimens is here presented. A numerical scheme to simulate full crack propagation is proposed which makes use of interface laws relating interlaminar stresses to displacement discontinuities along the plane of crack propagation. The relation between interface laws and mixed-mode failure loci in terms of critical energies is discussed and clarified. Numerical simulations are presented and compared with analytical and experimental results.

A mesomodel for localisation and damage computation in laminates

The basic aspects of a material mesomodel dedicated to composite laminates and capable of simulating complete fracture phenomena are discussed. Attention is focused herein on damage computation and, in particular, on the description of localisation phenomena. Both quasi-static and dynamic loadings are considered.

Identification and forecast of delamination in composite laminates by an interlaminar interface model

Abstract For the forecasting of delamination initiation and propagation, a previously defined meso-scale damage model of composite laminates is used. At the meso scale, the laminate is described as an assembly of damageable layers and interlaminar interfaces. The aim of this work is to identify precisely the interlaminar interface model for ±θ interfaces, with θ = 0 °, 22.5 ° and 45 ° being the relative directions of the fibres of adjacent plies. This identification is based on initiation and propagation delamination tests. Our analysis of the conventional propagation tests makes use of the links existing between the critical-energy release rates and some of the models parameters. In taking into account the part of the energy dissipated inside the layers, the interfaces can be classified into two categories: the 0 °/0 ° interfaces of brittle behaviour, and the interfaces at disorientated angles whose criticalenergy release rate is greater. Standard edge-delamination tension tests are also conducted and analysed in order to identify the other parameters of the interface damage model.

Geometrical and interfacial non-linearities in the analysis of delamination in composites

The subject of this paper is the study of interactions between delamination and geometrical nonlinearities. This problem generally addressed by means of Fracture Mechanics, is here treated by modelling interfacial degradation through irreversible, softening interface constitutive laws. Geometrical nonlinearities are associated to large displacements of thin layers which are assumed to be hyperelastic. A general formulation is presented and then specialised to the case of rectilinear laminated beams. Numerical aspects concerning finite element implementation are discussed together with a local control algorithm for the treatment of unstable paths. Numerical examples showing the effect of interaction between geometrical and material nonlinearities are presented.

Delamination analysis by damage mechanics: Some applications

Delamination is a phenomenon which involves complex degradation of both layers and inter-laminar connections. To take into account these degradations, the composite laminate is modeled at a meso scale as a stacking of homogeneous layers connected by interfaces. Layers and interfaces may be damaged. Both onset of delamination and its propagation on a short distance are predicted. Two applications are presented, the numerical simulations are compared with experimental results: (i) delamination in the vicinity of a straight edge of a specimen under tension or compression, (ii) delamination near the hole of a perforated plate under tension.

A delay damage mesomodel of laminates under dynamic loading: basic aspects and identification issues

This paper deals with the modeling of damage in laminates under dynamic loading. In the first part, the basic aspects of the model, which were developed in previous studies, are described. In the second part, we focus on current developments concerning the identification of the model using dynamic experiments. Since the applications are related to the design of composite crash absorbers, particular attention is given to the dissipation of energy.

Damage Mechanisms Modeling for Ceramic Composites

For ceramic composites, continuum damage mechanics models are built, which include information coming from both the micro and macro scales. These models are constitutive relations which, when included in a structural analysis code, are able to predict the damage state of the studied structure at any time and at any point until final fracture.

Some aspects of interlaminar degradation in composites

The subject of this paper is the use of interface models for the study of interlaminar degradation in composite materials. In the presentation the interface is considered as an independent material surfacic entity with its own constitutive characteristics. The main point which is discussed concerns the identification of interface material models.