Predicting density effects on the shock initiation of heterogenous high explosives

Variations in the density of a heterogenous high explosive affects shock initiation behavior. This occurs due to the associated variations in the microstructure (porosity, surface area, etc.), which affect the hot-spot initiation process. In this work, we quantitatively explored the effect of density variation using a physics-informed reactive flow model, the so-called Physically-Informed Scaled Uniform Reactive Flow model (πSURF). In previous work, we have used the model to gain insight into the role of porosity, pore size distribution and initial temperature in explosive performance. The model allows us to calculate the fraction of the porosity/specific surface area ignited for a given shock strength which drives the overall reaction rate. We can therefore see the effect of density variation by calculating the change in the number density of critical hot spots, or alternatively, the shock-activated specific surface area. Here, we explore the model predictions for the explosive PBX 9501 at densities of 1.826, 1.830 and 1.837 g/cc in the form distance-to-detonation and compare the results to experimental data. We found a favorable comparison. The physically-based model structure provides clearer and more quantitative insight into the mechanism of the influence of density on shock sensitivity.