Abstract:
In the field of explosive science, the existence of the ‘hot-spot’ is generally accepted
as essential to any theory on shock initiation. Continuum-based shock initiation
models only account for ‘hot-spots’ implicitly, and the majority of these models
use pressure-dependent reaction rates. The development of a simple but physically
realistic model to predict desensitisation (double shock) effects within the confines
of an existing pressure-based model is described and simulations compared with
experimental data with mixed results. The need to invoke a separate desensitisation
model for double shocks demonstrates that reaction rates are not substantially
dependent on local pressure.
The newly developed continuum, entropy-dependent, CREST model has been
implemented and validated in a number of hydrocodes. However, the move to
entropy-based reaction rates introduces a number of computational problems not
associated with pressure-based models. These problems are described, in particular,
an entropy-dependent model over-predicts the rate of energy release in an explosive
adjacent an impact surface, and requires a finer mesh than a pressure-dependent
model to achieve mesh converged results. The CREST model, fitted only to onedimensional
data of the shock to detonation transition, is shown to be able to accurately
simulate two-dimensional detonation propagation data. This gives confidence
in the predictive capability of the model.
To account for ‘hot-spots’ explicitly, a simple model to describe ‘hot-spot’ initiation
has been developed. The simple model is presented where ‘hot-spots’ are
formed as a result of elastic-viscoplastic stresses generated in the solid explosive
during pore collapse. Results from the model compare well with corresponding results
from direct numerical simulations, and both are consistent with observations
and commonly held ideas regarding the shock initiation and sensitivity of heterogeneous
solid explosives. The results also indicate that viscoplastic ‘hot-spot’ models
described in the literature are built on an invalid assumption.
