The Response of Energetic Materials under Focusing Shock Waves

Energetic materials (EMs) like cyclotrimethylene trinitramine (RDX) are known for their mechanical-driven decomposition. Their usage has been demonstrated in engineering, construction, and armament applications. We use a tabletop setup to shape a laser pulse into configurable ring patterns in an absorbing 50-um polysulfone layer to launch a 2D-confined focusing shock wave that converges towards a micron-sized EM crystal. The halfway pressure reaches a few dozen GPa, estimated by the shock speed between the ring and target. The shock-induced responses are recorded by in-situ single-frame femtosecond (fs) imaging and multi-frame ultrahigh-speed camera. In addition, various ring configurations (i.e., full, split, and half rings) are explored, evaluating different states of stresses to the resultant transient and permanent responses of insulted EM crystal. We also demonstrate EM responses under repetitive shock waves over 3000 times using a nondestructive multiple-ring system. Lastly, we employ fs-laser machining to purposely induce void, generating a hot spot to accelerate crystal decomposition. The resultant permanent changes in chemical and physical properties are investigated by Raman spectroscopy and scanning electron microscopy. Our observation provides new insight into the dynamic responses of randomly oriented EM crystals subjected to geometrically distorted shock waves that are present in real-world polymer-bonded explosives.