Peel-off case failure in thermal explosions observed by the deflagration cylinder test

We have discovered a previously unidentified thermal explosion mode using the Los Alamos deflagration cylinder test (DFCT). The DFCT is a “pipe bomb”-style test similar to the detonation cylinder test (DTCT), which has been used for many years to calibrate detonation product equations of state. The shot is heated in an oven to a uniform test temperature. The pre-heated high explosive (HE) is triggered by a hot wire initiator on one end. The tube is back-illuminated by a bright light source, and its combustion-driven deformation and subsequent break-up are observed by a high-speed framing camera. Like the DTCT, the DFCT tube wall motion provides the primary diagnostic. A variety of reactive responses are possible, including quasi-steady deflagration and deflagration-to-detonation transition. This paper focuses on the behavior of the HMX-based explosive PBX 9501 at 155 °C. Under this condition burning appeared to occur only at the HE/tube interface, causing the tube to peel away from the HE core. Peel-off propagated as a wave that traveled along the tube at ∼500 m/s. This failure mode resulted in vigorous case venting, but the response was otherwise benign. We derive a steady peel-off-wave model that reproduces the essential observed features for realistic PBX 9501 parameter values.