Rheological Properties of DNAN/HMX Melt-cast Explosives : Maximum Packing Density Calculation and Modified Viscosity Model

The study of suspensions with high solid content and low viscosity has become a very active topic for melt-cast explosives, for both research and industry. Previous studies have described how the viscosity of high-solid-content suspensions can be decreased by optimizing the grade ratio, that is, increasing the particle packing density. This paper numerically simulates the maximum packing density (Φm) for different grade ratios at which the suspension viscosity approaches infinity, using the overlapping discrete element cluster method. According to this method, the shape of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) particles was modeled as a group of overlapping, rigidly connected hard spheres. The results showed that the numerical simulation value can be used as the real value of Φm for any grade ratio in engineering applications. The rheological properties of 2,4-dinitroanisole (DNAN)/HMX suspensions with various grade ratios of three HMX samples with different d50 values were investigated using a rotational viscometer over a range of mass solids content (ϕ = 20-75 wt.%) in the shear rate range of 0.1-100 s⁻¹. An empirical model incorporating the reduced solid content (Φ, equal to ϕ divided by Φm) and shear rate (γ) was modified to predict the relative viscosity of DNAN/HMX suspensions. This modified model has a strong correlation with the experimental data and can be used to accurately predict the viscosity of DNAN/HMX suspensions. In addition, the applicability of different classical models to DNAN/HMX suspensions is discussed.