Obtaining cookoff data for explosives containing ammonium nitrate (AN) is difficult due to multiple polymorphic phase changes, low melting points, corrosive decomposition gases, catalytic reactions involving nickel or platinum thermocouples, and ignition failures in vented experiments. Despite these challenges, we have measured thermal ignition times for fertilizer grade AN (FGAN), pure technical grade AN (TGAN), AN with aluminum (ammonal), AN with fuel oil (ANFO), and AN with nitromethane (ANNM). The thermal ignition times for AN, ammonal, and ANFO were similar. In contrast, measured thermal ignition times for ANNM were much faster. The most reliable thermal ignition data were for AN and ANNM experiments that did not contain any internal thermocouples. A universal cookoff model (UCM) coupled to a micromechanics pressurization (MMP) model was used to accurately predict thermal ignition for these AN-containing explosives.

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This letter is an expanded response to the comments made on the paper “a generalization of the shock invariant relationship” presented at the ISEM 2024. The purpose of this short communication is to show that the generalized relationship can be obtained based on the velocity fluctuation correlation function approach as that based on select chemical kinetic equations. In the correlation approach the generalized relationship results from a particular choice of correlation function well known in the experimental study of solids comminution.

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