Schleiren imaging gives a better understanding of blast initiation

July 22, 2009
If you plan not only to have a blast, but to try to understand it too, Specialised Imaging (Tring, England) can help. The company has released a new application note describing how its SIM-8 ultrahigh-speed framing camera has been used to show the full development of a blast-initiation event.

If you plan not only to have a blast, but to try to understand it too, Specialised Imaging (Tring, England) can help. The company has released a new application note describing how its SIM-8 ultrahigh-speed framing camera has been used to show the full development of a blast-initiation event.

The development of short-duration electrical-pulse detonators such as the exploding bridge wire and exploding-foil initiator allows initiation of secondary explosives to be done with a higher level of safety, repeatability, and reliability than can be done with traditional hot-wire detonators. However, with the development of these new detonation systems, diagnostic techniques capable of accurately characterizing detonator functionality are required.

The application note describes how a spark source was placed behind the event to produce, with the SIM-8, a pseudo-schlieren imaging system able to see through the bright flash produced by an exploding-foil (or slapper plate) blast initiator, which normally obscures the ejection of the disc and fragments. Framing data (50 ns exposures at a 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.

Unlike many traditional ultrafast framing cameras, the 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, inherent in other designs, are eliminated and the high spatial resolution (greater than 36 lp/mm) is the same from frame to frame and in both axes. Individual ultrahigh-resolution intensified CCD detectors, controlled by state-of-the-art electronics, offer continuous control over gain and exposure, giving researchers the freedom to capture images of even the most difficult transient phenomena.

A copy of Application Note 8 may be downloaded from http://www.specialised-imaging.com/application_notes.htm.

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.

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