Marina Fazzini

Shear Test on CFRP Full-Field Measurement and Finite Element Analysis

The purpose of this work is to study the Iosipescu shear test and more precisely its ability to characterize the shear modulus of a carbone/epoxy composite material. The parameters influencing this identification are the fibre orientation, the geometry of the notch and the boundary conditions. Initially these parameters were studied through the finite element analysis of the shear test. Then, the measurement of the shear strains was carried out by traditional methods of measurement (strain gauges) but also by optical methods. These optical methods: the digital image correlation and the electronic speckle pattern interferometry (ESPI); allow for various levels of loading, to reach a full-field measurement of the shear strain. This enabled us to study the strain distribution on the section between the two notches. The finite element model enabled us to study the parameters influencing the calculation of the shear modulus in comparison with strain gauges, image correlation and ESPI. This work makes it possible to conclude on optimal parameters for the Iosipescu test.

Identification of Materials Properties Using Displacement Field Measurement

The aim of this work is to identify parameters driving constitutive equations of materials with displacement field measurements carried out by image stereo-correlation during an unidirectional tensile test. We evaluate two identification techniques. The first one is the virtual fields method which consists in writing the principle of virtual work with particular virtual fields. It is generally used in the case of linear elasticity and it requires a perfect knowledge of the model in terms of boundary condition since the virtual fields used must be kinematically admissible. This method allows to determine parameters by a direct and fast calculation, without iterations. The second method is the finite element model updating method. It consists in finding constitutive parameters that achieve the best match between finite element analysis quantities and their experimental counterparts. This method is more adaptable than the virtual field method but it needs to spend more calculation time.

Flambement d’un panneau composite auto-raidi réalisé par infusion de résine : Étude numérique et expérimentale

Un panneau composite auto-raidi representatif d’un fuselage d’avion est etudie. Ce panneau est fabrique selon un procede d’infusion de resine LRI (Liquid Resin Infusion) qui permet d’integrer des structures dans deux directions des les premieres etapes de la fabrication. L’etude numerique par elements finis vise a mettre au point un essai de post-flambement. L’essai de post-flambement valide experimentalement des modeles numeriques vis-a-vis de la charge et du deplacement a rupture. Des systemes de mesure optique par stereo-correlation d’images sont utilises pour comparer les resultats numeriques et experimentaux des deplacements hors plan. Aussi, le phenomene de decohesion se produisant dans la zone de peau-raidisseurs est mis en evidence a l’echelle globale.

Digital image stereo-correlation applied to the identification of elastomers

As a complement to classic characterization in the identification of elastomers, full-field measurement methods such as image stereo correlation can undeniably contribute to the validation of elastomeric connection behaviour. Indeed, these measurements enable three-dimensional displacement and strains fields over the totality of the studied surface to be finely reached. Characterization tests in shearing on an elastomer were followed by image stereocorrelation up to high strain levels. The experimental results could thus be confronted with theoretical results using an Alexander hyperelastic behaviour law, which enabled the relevance of this law to be validated locally.