We produce cellular material based on the formulation of model emulsions whose drop size and composition may be continuously tuned. The obtained solid foams are characterized by narrow cell and pore size distributions in direct relation with the emulsion structure. The mechanical properties are examined, by varying independently the cell size and the foam density, and compared to theoretical predictions. Surprisingly, at constant density, Young's modulus depends on the cell size. We believe that this observation results from the heterogeneous nature of the solid material constituting the cell walls and propose a mean-field approach that allows describing the experimental data. We discuss the possible origin of the heterogeneity and suggest that the presence of an excess of surfactant close to the interface results in a softer polymer layer near the surface and a harder layer in the bulk.

International audienceIn this article, the Discrete Element Method (DEM) is taking advantage for the damage modeling of a composite material. At this stage of work, a Representative Elementary Volume (REV) of an unidirectional composite material modeled in 3D is considered to prove the relevance of the approach. The interest to introduce the Discrete Elements (DE) on the scale of constituents (fiber and matrix) is to be able to report local mechanisms of degradation such as the matrix micro-fissuring, the fiber/matrix debonding and the break of fiber, appropriate to this type of material. The short-term objective is to use this DEM modeling to treat locally the damages induced by an impact loading associated with a conventional Finite Element modeling beyond the damaged zone. First, the geometrical modelings of the fiber and the matrix are presented. The phase of calibration of the DE model intrinsic parameters governing the fiber and matrix behavior and the fiber/matrix interface is afterward retailed. At this stage, each constituent is assumed to be brittle elastic. Then, simulations of longitudinal and transversal tensions but also of in plane and out of plane shearing are performed on the REV using DEM. The results are discussed and compared with those known for the literature. The capacity of the present DEM to capture the crack paths is particularly highlighted

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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. a b s t r a c tFoams, and particularly the polypropylene foam, are more and more often used in the area of injury protection and passive safety for its energy absorption capacity. This multi-scale material is constituted of mesoscopic beads with a large variability of the material properties. To study the effects of these mesoscopic heterogeneities on both the macroscopic and the local behaviors, numerical simulations on virtual volumes of foam under dynamic loading have been performed. The influence of the organized system of heterogeneities has also been studied in the cases of a random distribution and a multi-layered volume. Experimental dynamic compressive tests have been performed on multi-layered volumes of foam and compared with the results of the Finite Element Method.

No standardised device is available yet to measure contact forces continuously during transverse impacts caused by a projectile on a metal plate or a thin-walled structure. This study describes the design and validation phases of an instrumented projectile (mass = 1 kg) that can be used to achieve such measurements. The impact force, indeed, is computed from the strain data collected by some strain gauges glued on to a projectile part, which remains elastic during shock. Under numerically defined conditions, the projectile geometry makes it possible to record signals that are not disturbed by the reflections of the compressive and tensile strength waves appearing inside the projectile during and after shock. Gauge signal post-filtering is then virtually useless. The strain gauge-instrumented projectile sensitivity is used to study the effects of small clamping pressure variations during the transverse impact study on shipbuilding steel plates. A second application deals with the impact of an automotive steel dome initially drawn with a bulge test apparatus.