| dc.description.abstract | This thesis concerns crack growth phenomena in rubber. It is widely known
that a relationship exists between the magnitude of the stored energy release rate
available to drive a crack, called the tearing energy (7'), and the resultant crack
growth rate. For rubbers this basic relationship is said to be a characteristic of the
material. The magnitude of T is related to both the visco-elastic losses and the crack
tip diameter (d) However the actual size of d and its relationship with the viscoelastic
losses is not clear. This thesis examines the crack growth behaviour in relation
to d and the visco-elastic losses for a wide range of rubbers, whose visco-elastic
properties are altered either by swelling in a liquid, altering the test temperature or
the cross-link density and by the incorporation of fillers. Static, constant T, crack
growth tests were carried out. These revealed that two different crack growth
processes exist. For the fast crack growth process, T is determined by variations in
the visco-elastic losses alone. For the slow crack growth process, T is determined by
variations in both the visco-elastic losses and d. It is proposed here that the factors,
which alter d, are associated with cavitation ahead of the crack tip for unfilled
materials and with strength anisotropy for carbon black filled materials.
In cyclic crack growth tests, the crack growth per cycle, dc/dn, can be
considered to result from the sum of time and cyclic dependent crack growth
components. For the first time, the detailed magnitudes of the contribution of each of
these components to dc/dn have been determined, for a wide range of materials and
mechanisms responsible for this behaviour are postulated. Also crack growth tests,
both static and cyclic, were extended to very large extensions. Lastly this
investigation revealed that the tensile strength for both ciystallising and noncrystallising
rubber can be predicted using the tearing energy concept for a variety of
loading regimes. | en_US |
