Damage and hotspot formation simulation for impact-shear loaded PBXs using combined microcrack and microvoid model

A physically-based damage-hotspot formation framework incorporating multiple stress-state motivated evolution-modes of microcracks and microvoids is developed to study the overall damage behavior of polymer-bonded explosives (PBXs). Localized heating sub-models of shear-crack friction and void collapse hotspot mechanisms are described to predict impact-shear ignition of PBXs. Several features of microdefect evolution under a combined shear and compression loading are predicted as follows. (i) Crack growth causes an elasticity deterioration and softening response; (ii) void distortion begins at the yield point and ends at the softening point; (iii) the softening stage will be interrupted if the increasing lateral pressure is sufficiently large to inhibit crack growth; and (iv) void collapse occurs if the lateral pressure continually increases to a critical high value. Simulated results of a punched PBX charge show that shear-crack friction heating plays a critical role in ignition under low-velocity impact (<400 m/s). Under high-velocity impact (>400 m/s), the heating due to void collapse dominates ignition because the timescale to void hotspot formation (~1 μs) is considerably shorter than that of crack hotspots (~10 μs).