Experimental investigation of the fragmentation of metallic rings under dynamical radial expansion

Under explosive loading, thin-cased structures made of ductile material, e.g. air-launched warheads, undergo radial expansion until fragmentation occurs. The knowledge of the fragment population (mass, number, velocity, angle of ejection) helps to estimate the extent of lethality area. In literature, some theoretical, experimental and numerical studies consider simplified configurations such as ring expansion in order to get a better insight in the processes governing fragmentation. In this line, a new experimental set-up, namely the plate-impact-driven fragmentation test (PIDRET), has been developed for expanding ring using a single-stage gas gun. A steel projectile launched by the gas gun impacts a thin polymer disk circled by a metallic ring. Compressed against a thick anvil, the polymer disk flows radially putting under pressure the ring inner surface. The ring expands then homogeneously, reaching a hoop strain rate value close to 10⁴ s^-1, until fragmentation. Ultra-high-speed cameras and photon Doppler velocimetry (PDV) probes are used as time and space resolved diagnostics. Tests carried out on rings made of different metals and alloys evidence the strong dependence of the expansion kinematics and fragmentation process on the nature and state of the material.