Three-dimensional burning crack dynamics in constrained spherical explosive: visualization analysis and cavity-coupled pressure modeling

Accurate characterization of three-dimensional burning crack propagation remains pivotal yet challenging for energetic material safety, as conventional diagnostics and models inadequately resolve coupled crack-pressure dynamics in confined explosives. This study combines a novel spherical confinement system (with/without sapphire windows) with synchronized high-speed imaging and 3D reconstruction to overcome optical limitations in opaque explosives. Experimental analysis of centrally ignited HMX-based PBX-1 reveals: (1) burning cracks propagate radially with equatorial acceleration and polar deceleration, (2) systematic formation of 3–4 dominant crack branches across geometries, and (3) pressure evolution exhibiting gradual accumulation (subsurface cracking) followed by exponential growth (surface burn-through), with decay governed by cavity expansion. Building on Hill's framework, we develop a model incorporating cavity volume and fracture toughness criteria, validated against PBX explosive (95% HMX-based) experiments. The model demonstrates improved prediction of pressure trends compared to prior approaches, particularly in resolving laminar-phase accumulation and crack-induced surge transitions. Results establish structural cavity volume as a critical modulator of measured pressure and reveal direction-dependent crack kinematics as fundamental features of constrained combustion. This work provides experimentally validated insights into mechanisms of reaction pressure development and burning cracks pathways during constrained PBX explosive combustion.