Determining the Reaction Zone Length in Shock Initiated PETN

Pentaerythritol tetranitrate (PETN) is a secondary explosive used in electrical detonators in the form of a pressed powder. The reaction zone length of PETN is smaller than that of most other explosives, therefore there is a lack of data due to insufficient resolution of existing methods. Furthermore, most prior work has been on steady state behaviour, so the transition regime before steady state is particularly poorly understood. The research described in this thesis was undertaken in order to characterise the reaction zone length and wave curvature during the evolution from initiation to steady state. The investigation was focused on a detonator setting, so confined cylindrical pellets of a similar scale were used here. To separate the effect of the chemical reaction from the mechanical response to shock, plate impact experiments were performed on an inert simulant: a fine icing sugar with comparable particle size. The shock velocity and rise time were found to exhibit dependence on the thickness of the bed, suggesting that these effects may also play a role in PETN prior to development of detonation. A fibre launched laser flyer detonator system was constructed to allow repeatable shock initiation of the target samples with a high throughput. This apparatus could produce a highly tuneable shock without much of the electrical noise present with electrical detonators. High-rate capacitive sensing was applied as a technique for measuring detonation properties in small columns of PETN. Development of the diagnostic incorporated design of the sensor itself, event synchronisation handling and noise reduction. A custom-made data processing algorithm was used to extract useful information from the sensor signal. This technology was found to have the temporal and spatial resolution required, as well as being cheaper and easier to implement than competing methods. Experiments using this diagnostic were performed to measure the reaction zone length and curvature for a range of densities and sample sizes. The data could also be used to calculate detonation velocity and 'lost time'. An important part of these experiments was the creation of consistent target samples. A hydrocode incorporating the CREST reactive model was written to numerically model the detonation and provide a predictive capability. The results of the experiments were used to set the values of the parameters in the simulation.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2022

Author dc:creator

• Edgeley, James

Advisor dc:contributor.advisor

• Braithwaite, Chris

• Capacitive Sensing
• Detonation
• Explosive
• PETN
• Reaction Zone

Licence

• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

Author Identifier

0000-0003-4319-9374

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/342850