PETN Rate Stick and Cylinder Expansion Test Assemblies at the 3 mm Scale

The explosive pentaerythritol tetranitrate (PETN) is commonly used for detonators, detonating fuses, and booster assemblies. It has a spatially small reaction zone (measured in microns) that is advantageous for these applications and supports detonation function at very small scales. However, the small reaction zone and scale of typical applications requires performance testing at small scales to generate data for model calibration. Here we discuss the construction and fielding of 3-mm-diameter rate sticks and cylinder expansion (CYLEX) tests for PETN with a density of 1.65 g/cc. These small tests utilized similar assembly and diagnostic techniques as the larger versions typically fielded for other explosives except in the details of how they were implemented. Specifically, the rate sticks were constructed from 3 mm pellets bonded together in a precision fixture, and utilized ionization wires or a streak camera measurement to record the detonation velocity. A mirror destruct technique was also utilized to measure the front curvature (the first such measurements for the explosive). For the CYLEX test, the standard confiner dimensions (which are designed for a 25.4 mm charge diameter) were scaled to the 3 mm charge diameter, and rather than using shorting wires to measure detonation velocity, PDV was used to measure both detonation velocity and confiner motion. To manufacture the confiner, a combination of electron discharge machining (EDM) and conventional machining was used. In spite of the small scale of these tests and diagnostic differences, all tests yielded full data return. Most notably, given the thin wall of the CYLEX test (0.3 mm), wall expansion records did not exhibit any sign of early wall failure. The corresponding products equation of state model reduction is found to scale consistently with prior PETN results at other densities and test spatial scales.