Frédéric Dau

Rubber Impact on 3D Textile Composites

A low velocity impact study of aircraft tire rubber on 3D textile-reinforced composite plates was performed experimentally and numerically. In contrast to regular unidirectional composite laminates, no delaminations occur in such a 3D textile composite. Yarn decohesions, matrix cracks and yarn ruptures have been identified as the major damage mechanisms under impact load. An increase in the number of 3D warp yarns is proposed to improve the impact damage resistance. The characteristic of a rubber impact is the high amount of elastic energy stored in the impactor during impact, which was more than 90% of the initial kinetic energy. This large geometrical deformation of the rubber during impact leads to a less localised loading of the target structure and poses great challenges for the numerical modelling. A hyperelastic Mooney-Rivlin constitutive law was used in Abaqus/Explicit based on a step-by-step validation with static rubber compression tests and low velocity impact tests on aluminium plates. Simulation models of the textile weave were developed on the meso- and macro-scale. The final correlation between impact simulation results on 3D textile-reinforced composite plates and impact test data was promising, highlighting the potential of such numerical simulation tools.

Discrete-Continuum Coupling Method to Simulate Highly Dynamic Multi-Scale Problems: Simulation of Laser-Induced Damage in Silica Glass

Complex behavior models (plasticity, crack, visco-elascticity) are facing several theoretical difficulties in determining the behavior law at the continuous (macroscopic) scale. When homogenization fails to give the right behavior law, a solution is to simulate the material at a mesoscale using the discrete element model (DEM) in order to directly simulate a set of discrete properties that are responsible for the macroscopic behavior. Originally, the discrete element model was developed for granular material.

A multiscale separated representation to compute the mechanical behavior of composites with periodic microstructure

The requirements for advanced numerical computations are very high when studying the multiscale behavior of heterogeneous structures such as composites. For the description of local phenomena taking place on the microscopic scale, the computation must involve a fine discretization of the structure. This condition leads to problems with a high number of degrees of freedom that lead to prohibitive computational costs when using classical numerical methods such as the finite element method (FEM). To overcome these problems, this paper presents a new domain decomposition method based on the proper generalized decomposition (PGD) to predict the behavior of periodic composite structures. Several numerical tests are presented. The PGD results are compared with those obtained using the classical finite element method. A very good agreement is observed.

Experimental Investigation and Discrete Element Modelling of Composite Hollow Spheres Subjected to Dynamic Fracture

This paper deals with the characterization and the numerical modelling of the collapse of composite hollow spherical structures developed to absorb energy during high velocity impacts. The structure is composed of hollow spheres (  mm) made of epoxy resin and mineral powder. First of all, quasi-static and dynamic (  mm·min−1 to  m·s−1) compression tests are conducted at room temperature on a single sphere to study energy dissipation mechanisms. Fracture of the material appears to be predominant. A numerical model based on the discrete element method is investigated to simulate the single sphere crushing. The stress-strain-time relationship of the material based on the Ree-Eyring law is numerically implemented. The DEM modelling takes naturally into account the dynamic fracture and the crack path computed is close to the one observed experimentally in uniaxial compression. Eventually, high velocity impacts (  m·s−1) of a hollow sphere on a rigid surface are conducted with an air cannon. The numerical results are in good agreement with the experimental data and demonstrate the ability of the present model to correctly describe the mechanical behavior of brittle materials at high strain rate.

Évaluation de la dispersion des propriétés mécaniques d’un matériau composite par sous-échantillonnage

Dans cet article est presentee une technique de sous-echantillonnage et d’homogeneisation destinee a rendre compte des variabilites de comportement dans les materiaux composites a l’echelle mesoscopique. Ces variabilites sont mises a profit dans des modelisations multi-echelles. La technique proposee est mise en oeuvre pour caracteriser le comportement transverse des plis unidirectionnels dans un composite a matrice organique (CMO) stratifie. Une modelisation par la methode des elements finis (MEF) de la microstructure est realisee a l’echelle microscopique a partir d’une micrographie transverse d’un pli. Une partie de cette micrographie representative du materiau (echantillon) est etudiee avec l’hypothese de deformations planes. Une procedure d’homogeneisation de sous-domaines de l’echantillon est developpee en post-traitement d’un calcul EF reduit a trois cas de chargement elementaires pour obtenir les proprietes effectives du sous-domaine ou sous-echantillon. Seules les proprietes elastiques sont considerees a ce stade des travaux. Plusieurs scenarios de sous-echantillonnage sont realises en faisant varier la taille et les positions des sous-domaines, selon un schema spatial regulier, pour generer des distributions statistiques de proprietes elastiques. L’identification de ces distributions a montre un effet d’inference statistique au schema spatial. Des sous-echantillonnages spatialement aleatoires sont realises pour preciser son influence sur les fonctions de distributions.