High-speed imaging improves understanding of blast initiation
JULY 29, 2009--The development of new detonation systems requires diagnostic imaging techniques capable of accurately characterizing detonator functionality. Using a SIM-8 ultra-high speed framing camera, Specialised Imaging (Tring, UK; www.specialised-imaging.com) has demonstrated such a system.
Applied to short-duration electrical-pulse detonators such as the exploding bridge wire and exploding foil initiator, it would allow initiation of secondary explosives to be done with a higher level of safety, repeatability and reliability than is achievable with hot wire detonators.
A spark source was placed behind the event to produce, a pseudo-schlieren imaging system able to see through the bright flash produced by an exploding foil (or slapper plate) blast initiator that normally obscures the ejection of the disc and fragments. Framing data (50-ns exposures, 250-ns separation) is presented that clearly shows the shock waves from the blast as well as the ejected fragments.
The device slapper plate itself can be clearly seen in the later exposures being ejected vertically. The shockwave from the slapper plate is shown to have a very narrow mach angle which may be used to measure its velocity.
Tthe optical design of the SIM-8 provides the choice of up to 8 separate optical channels without compromising performance or image quality. Effects such as parallax and shading are eliminated and the high spatial resolution (> 36 lp/mm) is the same from frame to frame and in both axes.
Individual ultra-high resolution intensified CCD detectors, controlled by state-of-the-art electronics, offer control over gain and exposure, allowing researchers freedom to capture images of difficult transient phenomena.
A copy of the application note describing this demonstration (No. 8) may be downloaded from http://www.specialised-imaging.com/application_notes.htm.
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-- Posted by Conard Holton, Vision Systems Design, www.vision-systems.com