Schlieren imaging offers a better understanding of blast initiation

Specialised Imaging Ltd. has released a new application note describing how its SIM-8 ultra-high speed framing camera has been used to show the full development of a blast initation 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 is achievable with hot wire detonators. With the development of such detonation systems, diagnostic techniques capable of accurately characterising detonator functionality are required.

The application note describes how a spark source was placed behind the event to 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 (50ns exposures, 250ns 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 ultra fast 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 (> 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 almost infinite control over gain and exposure allowing researchers total freedom to capture images of even the most difficult transient phenomena.

Specialised Imaging Ltd. is a knowledgeable, dynamic company focused upon design, manufacture, service and supply of ultra high-speed imaging systems and components for industrial, defence and scientific applications.
For further information on this application please contact Specialised Imaging Ltd on telephone +44 (0) 1442 827 728 or email