Browsing by Author "Whitworth, N."

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    Mathematical and numerical modelling of shock initiation in heterogeneous solid explosives
    (Cranfield University, 2008-07-17T10:27:51Z) Whitworth, N.; Forth, S. A.
    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.