| dc.description.abstract | This study aims to understand the behaviour of a novel elastomer where hollow
microspheres are used as a particulate filler. The behaviour of elastomers filled with
rigid particles, is fairly well understood, where the stiffness increases as the amount of
filler material is increased, alternatively, foamed elastomers which are usually produced
with either closed cells or open cells, have been shown to become softer as the volume
of the voids are increased. When traditional foam materials are compressed they exhibit
non-linear behaviour in three distinct phases, the cell walls firstly bend, then they
buckle and this is followed by densification.
To understand the overall physical behaviour of the material, tensile tests of the
elastomer material were conducted using unfilled materials and filled with a range of
the hollow sphere filler volume fractions. Compression tests were also conducted on
small cylinders, again using unfilled and filled rubbers with a range of filler volume
fractions. The physical tests showed that increasing the filler volume fraction increased
the reinforcing effect at low strains with an associated increase in stiffness, but the
material then became increasingly less stiff at higher strains. To understand the
behaviour of the bulk material, the mechanical behaviour of single hollow spheres under
strain were investigated, both as a standalone material and then also embedded in an
elastomer.
To examine the mechanical behaviour of a single hollow plastic sphere a single
microsphere was compressed using nano-indentation, the tests were then replicated at a
larger scale using model table tennis balls. FEA software was used to model the
behaviour of both types of hollow sphere, as well as a wide range of other spheres to
better understand their buckling behaviour, to help predict the behaviour of
microspheres with different ratios of wall thickness to diameters.
To examine the behaviour of hollow spheres in a rubber matrix, simple
cylindrical unit cells were made with a single hollow plastic sphere embedded within
them. These model cylinders were produced with a translucent elastomer containing a
single table tennis ball. Their behaviour in compression and in tension and that of a
single hollow plastic sphere embedded in an elastomer was also modelled using FEA
software, the effects of debonding and buckling were determined for small and large
strains and were used to examine the more complex behaviour of the filled composite.
A comparison between the measured behaviour and the various models indicates that
the bulk behaviour of the microsphere filled elastomers is primarily determined by a
progressive dewetting process of the rubber away from the microsphere in tension and
by buckling phenomena of the hollow spheres in compression. | en_US |
