Simulation of dynamic delamination and mode I energy dissipation

Delamination initiation and propagation of aeronautic composites is an active field of research. In this paper we present a methodology for critical energy release rate correlation of numerical simulation and experimental data. Experiments of mode I critical energy release rate were carried out at quasi static and pseudo dynamic loading rates. Cohesive finite elements are used to predict the propagation of delamination in a carbon fiber and epoxy resin composite material. A bilinear material model is implemented via user defined cohesive material subroutine in LS-DYNA. The influence of mode I energy release rate in mixed mode loading, due to a low velocity impact, is also investigate

Dynamic delamination of aeronautic structural composites by using cohesive finite elements

Cohesive finite elements are used to model impact induced delamination prediction of T800/21M unidirectional laminated composite. DCB, ELS and MMB tests are used to identify cohesive element parameters. Results from experiments and numerical prediction of impact induced delamination by commercially available code LS-DYNA are compared

Damage location method for thin composites structures - application to an aircraft door

Piezoelectric sensors are widely used for Structure Health Monitoring (SHM) technique due to their high-frequency capability. In particular, electromechanical impedance (EMI) techniques give simple and low cost solutions for detecting damage in composite structures. For example, damage indicators computed from EMI deviations between the pristine structure and the damaged structure can be compared to a threshold in order to point damage. When it is question of damage localization, the simple analysis of the electromechanical impedance fails to furnish enough information. We propose a method based both on EMI damage indicators and on the acoustic attenuation level to locate damage. One of the main advantages of our method, so called data driven method, is that only experimental data are used as inputs for our algorithms. It does not rely on any model

Modelling aeronautical composite laminates behaviour under impact using a saturation damage and delamination continuous material model

We show that the behavior of T700/M21s and T800/M21s composite panels are affected by the influence of strain rates together with local shear and crush punch or global flexural strengths of the structure. A deterministic continuous composite material model has been developed as a LS-DYNA user defined material model for unidirectional composites on the basis of the Matzenmiller model widely used for woven composites. Initiation and evolution up to saturation and fracture are implemented for various and coupled damage mechanisms including delamination. Quasi-static and dynamic characterization tests laminates have been carried out on balanced angle ply [±θ] and used for calibration of numerical values. Impact induced damage from experiment's measures and numerical predictions are compared for T800/M21S aeronautical samples impacted at 15J

Smart EMI monitoring of thin composite structures

This paper presents a structural health monitoring (SHM) method for in-situ damage detection and localization in carbon fibre reinforced plates (CFRP). The detection is achieved using the electromechanical impedance (EMI) technique employing piezoelectric transducers as high-frequency modal sensors. Numerical simulations based on the finite element method are carried out so as to simulate more than a hundred damage scenarios. Damage metrics are then used to quantify and detect changes between the electromechanical impedance spectrum of a pristine and damaged structure. The localization process relies on artificial neural networks (ANN) whose inputs are derived from a principal component analysis of the damage metrics. It is shown that the resulting ANN can be used as a tool to predict the in-plane position of a single damage in a laminated composite plate

Damage localization map using electromechanical impedance spectrums and inverse distance weighting interpolation: Experimental validation on thin composite structures

Piezoelectric sensors are widely used for structure health monitoring technique. In particular, electromechanical impedance techniques give simple and low-cost solutions for detecting damage in composite structures. The purpose of the method proposed in this article is to generate a damage localization map based on both indicators computed from electromechanical impedance spectrums and inverse distance weighting interpolation. The weights for the interpolation have a physical sense and are computed according to an exponential law of the measured attenuation of acoustic waves. One of the main advantages of the method, so-called data-driven method, is that only experimental data are used as inputs for our algorithm. It does not rely on any model. The proposed method has been validated on both one-dimensional and two-dimensional composite structures

Smart monitoring of aeronautical composites plates based on electromechanical impedance measurements and artificial neural networks

This paper presents a structural health monitoring (SHM) method for in situ damage detection and localization in carbon fiber reinforced plates (CFRPs). The detection is achieved using the electromechanical impedance (EMI) technique employing piezoelectric transducers as high-frequency modal sensors. Numerical simulations based on the finite element method are carried out so as to simulate more than a hundred damage scenarios. Damage metrics are then used to quantify and detect changes between the electromechanical impedance spectrum of a pristine and damaged structure. The localization process relies on artificial neural networks (ANNs) whose inputs are derived from a principal component analysis of the damage metrics. It is shown that the resulting ANN can be used as a tool to predict the in-plane position of a single damage in a laminated composite plate

Elasto-Plastic Analysis of Bonded Joints with Macro-Elements

The Finite Element (FE) method could be able to address the stress analysis of bonded joints. Nevertheless, analyses based on FE models are mainly computationally cost expensive and it would be profitable to develop simplified approaches, enabling extensive parametric studies. Firstly, a 1D-bar and 1D-beam simplified models for the bonded joint stress analysis, assuming a linear elastic adhesive material, are presented. These models derive from an approach, inspired by the finite element (FE) method using a formulation based on a 4-node macro-element, which is able to simulate an entire bonded overlap. Moreover, a linear shear stress variation in the adherend thickness is included in the formulation. Secondly, a numerical procedure is then presented to introduce into both models an elasto-plastic adhesive material behavior, while keeping the previous linear elastic formulation. Finally, assuming an elastic perfectly plastic adhesive material behavior, the results produced by simplified models are compared with the results predicted by FE using 1D-bar, plane stress and 3D models. Good agreements are shown

Délaminage de matériaux composites à fibres de carbone et à matrices organiques : étude numérique et expérimentale, suivi par émission acoustique

Ces travaux concernent la tolérance aux dommages de type défauts d’impacts, de composites à matrices thermodurcissables (T300/914) et thermoplastique (AS4/PEEK). Afin de simuler des défauts d’impacts, des pastilles de téflon ont été insérées entre les couches des composites stratifiés, lors de la fabrication. L’objectif est donc de modéliser la tenue en compression de plaques stratifiées introduisant ces défauts. Après une parte bibliographique, le premier chapitre s’attache à identifier des modèles d’endommagements couplés à la pseudo-plasticité des résines pour les deux matériaux étudiés. Un modèle d’endommagement modifié a été implémenté dans SAMCEF® et des corrélations essais calculs sont présentées. Il apparaît que le comportement de l’AS4/PEEK est bien meilleur que celui du T300/914 ; la matrice PEEK ayant de meilleur caractéristiques mécaniques. La deuxième partie présente un ensemble de résultats de mécanique de la rupture (essais en mode I et II) sur éprouvette DCB t ENF, permettant de déterminer les énergies critiques de délaminage. L’influence de l’orientation des plis de part et d’autres de la préfissure permet de déterminer les énergies critiques de délaminage pour des interfaces désorientées. Deux méthodes numériques de calculs des taux de restitution d’énergie ont été développées et implémentées dans SAMCEF en linéaire et non linéaire : - La méthode VCE (Virtual Crack Extension) - La méthode VCC (Virtual Crack Closure) Ces deux méthodes ont été utilisées pour les corrélations essais-calculs sur les éprouvettes de mécanique de la rupture sur des modèles éléments finis 3D afin de déterminer la répartition des taux de restitution d’énergie le long du front de fissure. Concernant la propagation de délaminage, là encore le composite AS4/PEEK est bien plus tenace : les taux de restitution d’énergie critique en mode I et II sont 10 fois supérieurs à ceux du T300/914. Enfin, les résultats des deux chapitres précédents ont permis de développer des modèles de prévision de la tenue en compression de plaques stratifiés introduisant des délaminages. Les modèles sont non linéaires géométriques (flambement locale) et matériau (endommagement + plasticité + rupture des plis) et permettent par calculs des taux de restitution d’énergie le long du front de fissure et par utilisation d’un critère de propagation de délaminage en mode mixte, de prévoir l’apparition des délaminages en compression. Ces modèles ont permis de montrer notamment que l’apparition de macro-fissures dans les plis situés aux dessus des délaminages, guide la direction de propagation du délaminage

Contribution to the study of cylindrical adhesive joining

This paper presents a study of the stress analysis in cylindrical assemblies. For the present study we use a cylindrical assembly of two tubes. We write all the components of the stress field function of the Ϭ⁽¹⁾zz (z) stress in the first tube and then we introduce these components into the potential energy formulation. Our method is a variational method applied on the potential energy of deformation. The model can predict the intensity and the distributions of stresses in the assembly. We can also analyse the influence of some geometrical or material parameters on the stress field