A Liquid Stratification Model to Predict Failure in Thermally Damaged EBW Detonators

Abstract

In previous work, commercially available downward facing exploding bridgewire detonators (EBWs) were exposed to elevated temperatures. These detonators were then initiated using a firing set which discharged a high amplitude short duration electrical pulse into a thin gold bridgewire. Responses of the detonators were measured using photonic doppler velocimetry (PDV) and high-speed photography. A time delay of 2 μs between EBW initiation and first movement of an output flyer separated operable detonators from inoperable detonators or duds. In the current work, we propose a simple method to determine detonator operability from the calculated state of the detonator at the time the firing set is initiated. The failure criterion is based on the gap distance between the exploding bridgewire (EBW) and the adjacent initiating explosive within the detonator which is low-density pentaerythritol tetranitrate (PETN) that melts between 413-415 K (140-142 °C). The gap forms as PETN melts and flows to the bottom of the input pellet. Melting of PETN is modeled thermodynamically as an energy sink using a normal distribution spread over a temperature range between the onset temperature of 413 K and the ending temperature of 415 K. The extent of the melt is determined from the average temperature of the PETN. The PETN liquid is assumed to occupy the interstitial gas volume in the lower part of the input pellet. The vacated volume from the relocated liquid forms the gap between the EBW and the PETN. The remaining sandwiched layer consists of solid PETN particles and gas filling interstitial volume. We predict that a threshold gap between 17-27 μm separates properly functioning detonators from duds.

Preparation and properties of a new high-energy metal (W) film/aluminum nitride system energy exchanger electrothermal pyrogenant

“…In recent years, the application environment of pyrotechnic devices has become extreme and complex gradually, with higher requirements for their high safety and reliability. [10][11][12][13] However, electric pyrotechnic devices are linear energy exchangers, and most of them are prone to generating induced currents in complex electromagnetic environments to react to unexpected electromagnetic stimuli, heating the energy exchanger and causing accidental ignition or damage to the energy exchanger by thermal chemicals, 14 affecting its performance. Therefore, the damage mechanism is the same as the normal ignition mechanism, which means that if safety needs to be improved, the safety current (maximum non-ignition current) must be increased to passivate it, which will inevitably reduce reliability.…”