Articles techniques et présentations

Foam is a multiscale material composed of many millimetric cells. Altogether, the cells can easily be shaped into almost any object of the metric scale, provided that a mould is available to let the initial mixture expand appropriately. While some mechanical properties such as foam density can analytically be calculated from the bulk material and the void ratio, others cannot. Even the Young modulus and Poisson ratio of an isotropic foam are out of reach for analytical analysis: in this work, it will be demonstrated that mixing laws fail at correctly predicting their values. Indeed, the structural properties depend strongly on the micro-structure of the foam. In this work, periodic homogenization as described in Viry et al. [1] is applied to investigate the foam properties. The foam unit cell selected is based on Weaire and Phelan solids [2] that represent a periodical structure very close to foam structure. Indeed, the Weaire and Phelan pair of solids show two import properties: together, (a) they map the 3D space, and at the time of the study, (b) they are the periodical volumes verifying (a) that show the minimal surface to volume ratio. This latter property is mimicking accurately the energy minimization process involved in cell shape forming process. Thanks to the periodic homogenization method, the Young modulus and Poisson ratio are computed and applied to modelling a car seat under load. This allows for determining the seat shape under load. Moreover, periodic homogenization includes a relocation method, which is used to investigate the structural integrity of the cell wall and estimate the evolution of the foam properties over time. Therefore, such method is a powerful tool to study the replacement of traditional polymer-based composites and foams by environmentally respectful alternatives.