Multi-scale Foam Behaviour Characterisation
Author(s)
P. Viot & D. Bernard
Abstract
The mechanical behaviour of polymeric foams depends on several parameters
such as temperature, material density and strain rate. The identification of the
parameters characterizing this behaviour under dynamic loading requires the
design of special apparatus like a fly wheel, drop tower or Hopkinson bars,
allowing high compression speeds.
The foams studied here are multi-scale materials; the agglomerated beads
(mesoscopic scale, millimetric diameters) are composed of microscopic closed
cells (a few tens of microns). Constitutive materials of these foams are
polypropylene, polystyrene and cork. The response of the material to a dynamic
loading consists of three regions: an elastic phase, a plastic phase and
densification. The first part of this work deals with the identification of the
behaviour of these multi-scale foams as a function of density and strain rate. In
the second part, original observations of the physical phenomena initiated during
the yield plateau are presented and analysed. Buckling of bead and cell wall and
strong localisation of damage were studied using several devices and techniques
such as high speed cameras, SEM, and micro tomography.
Keywords: multi-scale foam, cellular material, dynamic loading.
1 Introduction
Polymer foams are used in many applications of passive safety for consumer
goods (packaging for electronic equipment…) or for consumers themselves
(helmets, knee pads…). It is usual to classify cellular materials in closed or
opened cell foams [1], but it is also important to distinguish between foams
which are constituted only of micro cells (commonly used in large plates for
thermal or sound isolation applications in civil engineering) and those composed
of fused beads (their size is millimetric and constitute the mesostructure) which
are themselves made of micro cells (figures 1 and 2).
Keywords
multi-scale foam, cellular material, dynamic loading.
Related Book
Other papers in this volume
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