Nadia Achour

Bio: Nadia Achour is an academic researcher from Arts et Métiers ParisTech. The author has contributed to research in topics: Tangent modulus & Viscoplasticity. The author has an hindex of 1, co-authored 2 publications receiving 17 citations.

Modélisation multi-échelles en viscoplasticité endommageable de composites thermoplastiques renforcés par des fibres discontinues

Abstract: Un nouveau modele multi-echelles en regime viscoplastique endommageable est developpe pour un composite a matrice polypropylene renforce par des fibres de verre courtes. Base sur l’approche en champs moyens de Mori Tanaka, il integre une matrice viscoplastique modelisee par un modele phenomenologique nomme par ses auteurs DSGZ et des fibres de verres modelisees par un comportement elastique lineaire. Le modele multi-echelles permet d’integrer la microstructure du composite prealablement caracterisee par la microtomographie aux rayons X. L’introduction de la matrice viscoplastique dans le modele de Mori Tanaka est rendu possible grâce a une implementation par integration implicite du modele qui permet d’obtenir le module tangent necessaire au mod ele d’homogeneisation. L’endommagement du materiau est integre a travers du mecanisme de decohesion de l’interface fibre/ matrice. Ce mecanisme d’endommagement est modelise par une loi cumulative de type Weibull. La dependance a la vitesse de deformation du composite observee lors des essais dynamiques est integree au moyen de la prise en compte de la viscosite de la matrice. Les parametres du modele sont identifies par une methode inverse sur la base d’essais de traction a differentes vitesses et pour differentes orientations d’eprouvettes. Le modele developpe a ete valide par comparaison avec des essais de traction.

Hierarchical micromechanical modeling of the viscoelastic behavior coupled to damage in SMC and SMC-hybrid composites

Abstract: The aim of this paper is to study, through a multiscale analysis, the viscoelastic behavior of glass reinforced sheet molding compound (SMC) composites and SMC-hybrid composites mixing two types of bundle reinforcement: glass and carbon fibers. SMC exhibit more than two distinct characteristic length scales, so that a sequence of scale transitions is required to obtain the overall behavior of the composite. An analytical procedure is used consisting of properly selected well-established micromechanical methods like the Mori-Tanaka (MTM) and the composite cylinders (CCM) accounting for each scale transition. After selecting a representative volume element (RVE) for each scale, the material response of any given length scale is described on the basis of the homogenized behavior of the next finer one. This hierarchical approach is appropriately extended to the viscoelastic domain to account for the time dependent overall response of the SMC composite material. The anisotropic damage has been introduced through a micromechanical model considering matrix penny-shape microcrack density inside bundles. The capabilities of the hierarchical modeling are illustrated with various parametric studies and simulation of experimental data for glass-based SMC composites.

Multi-scale experimental investigation of the viscous nature of damage in Advanced Sheet Molding Compound (A-SMC) submitted to high strain rates

Abstract: This paper aims to present an experimental multi-scale analysis of quasi-static and high strain rate damage behavior of a new formulation of SMC composite (Advanced SMC). In order to study its capability to absorb energy through damage accumulation, Randomly Oriented (RO) and High oriented (HO) A-SMC composites damage has been investigated at both microscopic and macroscopic scales. A specific device has been developed in order to perform Interrupted Dynamic Tensile Tests (IDTT) which allows analyzing the evolution of the microscopic damage mechanisms occurring during rapid tensile tests. Several damage micro-mechanisms have been pointed out. The relative influences of these micro-damage events and their interactions have been related to the macroscopic damage behavior through the definition of microscopic and macroscopic damage indicators. Damage threshold and kinetic have been quantified at various strain rate for different microstructures and loading cases (RO, HO-0° and HO-90°). It has been shown at both scales that increasing strain rate leads to an onset of damage initiation together with a reduction of the damage accumulation kinetic. Moreover, the influence of the fiber orientation has been studied in order to emphasize the anisotropic strain rate effect at the fiber-matrix interface scale. The latter was related to the influence of the microstructure of A-SMC composites. Finally, on the basis of the whole experimental results, the microscopic origin of the viscous nature of the damage behavior of A-SMCs composites have been discussed and related to the influence of the strain rate and microstructure.