Experimental and theoretical study of detonation phenomena in additive-manufactured high explosive structures

Abstract

The detonative performance of a High Explosive (HE) is closely related to charge geometry but traditional HE manufacturing constrains geometries to those that can be produced by pressing and conventional automated machining processes. Additive Manufacturing (AM) has recently been utilized to expand the HE design space and fabricate directionally-sensitive and “switchable” charges. However, the mechanisms for directional sensitivity and switchability are not thoroughly understood and the detonative performance of switchable charges has not been quantified. This research studies detonation phenomena in HE parts printed with octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)-based ink. Precursor Shock Wave (PSW) propagation was recorded in channels at velocities near 11 − 13 km/s and shock polar calculations suggest that the PSW is supported by a piston of detonation products moving ahead of the detonation wave. The PSW pre-compresses HE strands to pressures only slightly higher than those used to press similar HEs and the results cast doubt on dead-pressing as the mechanism for detonation directionality in stranded AM HE structures. Flash x-ray results could not verify the existence of detonation product pistons in internal channel regions but late reactions occurred in channel regions behind the detonation front and increased the pressure by 29-33% relative to the bulk structure. The performance of fluid-filled AM HE lattices was evaluated by analysis of detonation velocity and mechanical work done by the HE (the Gurney energy). The Gurney energy of an unfilled AM HE structure was 98% lower than that of an equivalent water-filled structure as the unfilled structure failed to sustain detonation. Higher density fill fluids reduced the detonation velocity by 13.4%. A combination of homogeneous and heterogeneous detonation mechanisms are suspected to exist in fluid-filled AM HE lattices. Reactive burn modeling should be used in future research to study detonation directionality in structures and additional experimental work is needed to minimize inter-strand gap spacings and maximize Gurney energy in switchable AM HE lattices.