On the account of a cohesive interface for modeling the behavior until break of highly filled elastomers

The nonlinear behavior and failure of highly filled elastomers are significantly impacted by the volume fraction, the size and nature of fillers and the matrix stiffness. Original experimental data obtained on glass beads reinforced acrylates and on propellants allow illustrating and discussing the main effects generally observed. In order to better understand the effects of the microstructure and constitutive parameters on the behavior and failure of highly filled elastomers, a composite model, represented by a 2D periodic cell with randomly dispersed particles, with an account of a cohesive zone at the filler/matrix interface is used. Finite element simulations with finite strain provide insight on the stress-strain responses dependence to the model parameters and allow defining a failure criterion perceived by the appearance of a critical fibrillar microstructure

A numerical study of the influence of polydispersity on the behaviour until break of a reinforced hyperelastic material with a cohesive interface

Solid propellants manufacturers commonly monitor the granulometries of the explosive fllers they introduce in the material to pack high fller volume fraction and thus obtain satisfactory energetic performance. However, to our knowledge, the effect of a mix of small and large particles in the micrometric size range in flled elastomers has not yet been fully understood. This work aims at producing a better understanding of the underlying mechanisms that take place in a bidisperse flled elastomer composite under uniaxial loading by using finite element simulations. An original process for creating bidisperse microstructures is proposed and analyzed. The key role of the fller/matrix interface is emphasized through the use of a cohesive zone model. Plane- strain simulations in uniaxial tension of such cells with different fractions of large and small particles are performed

Stress-strain response and volume change of a highly filled rubbery composite: experimental measurements and numerical simulations

The stress-strain response of a rubbery polymer network highly filled with micrometric glass beads was measured at low strain rate in uniaxial tension. The volume change of the glass bead filled material upon stretching was recorded by video extensometry and X-ray tomography scans were used to identify the type of damage within the composite material. The modeling used a cohesive-zone model from the literature depending on the polymer/glass adhesion energy that was measured by peeling polymer strips from a glass plate. Nonlinear finite element simulations were performed on representative three-dimensional microstructures defined by periodic cubic unit cells containing randomly dispersed spherical particles}. Good reproductions of both the composite response and the volume change were obtained prior to the appearance of inner cracks

Effects of small particles on the mechanical behavior and on the local damage of highly filled elastomers

The mechanical behavior and damage of highly filled elastomers such as propellants is studied experimentally. A model material made of a polyacrylate matrix filled with glass beads and energetic binders filled with ammonium perchlorate and HMX have been formulated. The focus is on materials containing micrometric size particles. The size of fillers was varied from a few microns to hundreds of microns in order to study the impact of the size of particles. The materials stress-strain responses and the volume changes during uniaxial tensile tests have been recorded. Microtomographic slices of strained samples have been obtained in order to look at the type of damage sustained by the acrylate/glass bead materials. It appears that in the presence of large particles, composites showing early prominent crack benefits from the addition of small particles, whereas composites showing well dispersed matrix/particle decohesion without large cracks show no change of behavior when small particles are added.financement DG

Propellant cohesive fracture during the peel test of a propellant/liner structure

The integrity of propellant/liner structures in rocket motors is critical to ensure controlled combustion of the engine. In an effort to improve the bonding between the liner and the propellant, it is necessary to characterize it well. Therefore, a propellant–liner structure, bounded thanks to co-curing, has been submitted to a peel test while recording the macroscopic fracture energy and the local displacement field on the propellant-free surface. The experimental setup includes two cameras in order to record the displacement field on the propellant-free surface. Upon loading, the peel force stabilizes quickly due to a cohesive fracture in the propellant, providing access to the fracture energy. While the crack propagates through the propellant, it is observed that only a small localized area is submitted to strain, and most of the structure remains unstrained

Stress-strain response and volume change of a highly filled rubbery composite: Experimental measurements and numerical simulations

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