In-situ tomography on damage evolution of solid propellant under dynamic loading

Structural damages in solid propellants can lead to combustion anomalies and affect ballistic performance. Utilizing synchrotron radiation X-ray computed tomography technology and an in-situ mechanical loading test system, the macro-meso structures of nitrate ester plasticized polyether (NEPE) solid propellant were observed in-situ at compressive rates of 0.1, 1.0, and 5.0 mm/s. The compressive process employed an intermittent loading mode. With loading paused each time the preset displacement was reached to enable scanning imaging, thereby capturing the state of the propellant at specific phases during compression. Following the in-situ imaging experiment, the tomographic images of the samples were processed through projection correction and phase recovery using PITRE and PITRE_BM software, followed by image bit-depth conversion to obtain 8-bit 2D grayscale slices. Through 3D reconstruction, the typical damages and evolutionary behaviors of the solid propellant were analyzed, exploring the macroscopic deformation as well as the distribution and propagation patterns of internal micro-cracks. Results indicate that most micro-cracks nucleate and grow at the interface between filled particles and the matrix, with meso-pore evolution being rate-dependent. Unlike the continuous damage growth under tensile loading, the nucleation, growth, and closure of pores occur simultaneously during compression. Under high-rate uniaxial compressive loading, the solid propellant exhibits characteristic trumpet-shaped deformation, with spatially distributed cracks primarily located around the propellant. Macroscopic surface damage results from micro-crack propagation between near-surface particles and the matrix, with crack propagation related to the spatial location of filled particles. Transversal and axial crack propagation modes exist under dynamic compressive loading, with the transition from vertically to horizontally oriented cracks in the matrix leading to crack closure.