A paper from Specialised Imaging describes how the Thiot Ingenierie Shock Physics Laboratory (Puybrun, France) is using its SIM-8 ultra high-speed framing camera.
The lab is using it to study high-velocity impacts of aluminium spheres against an aluminium target at velocities in excess of 4000m/s.
Beyond military applications, considerable interest has been shown by the air and space industries on basic research into hypervelocity impact behaviour of materials.
Applications for such research include enhancing the survivability of aircraft to in-flight explosions and in protecting valuable space satellites from damage from stellar debris.
To model a hypervelocity impact, Thiot Ingenierie undertook to accurately record a 3mm ball with a velocity in excess of 4000m/s - just before, at and after impact.
To allow the necessary accurate measurements of the projectiles just before impact it was determined that exposure times of 20 nanoseconds or less were required to reduce motion blur to less than the size of a pixel.
Consequential to such short exposure times was also the problem of producing adequate light levels to fully define the edges and the corners of the projectile.
Data shown in the application note was produced by a SIM-8 ultra high-speed imaging camera programmed for 200,000 frames per second with 20ns exposures.
The 3mm projectile was fired from a fixed two-stage light gas gun.
The event was backlit using a SI-AD500 flash lamp to provide adequate illumination for the complete event.
The high-resolution images from the SIM-8 clearly show the cloud of ejecta thrown backwards on impact and also demonstrate that even though the projectile disintegrates on impact, the fragments maintain the original projectile shape ahead of the main fragment cloud.
The test also showed that the remaining fragments do not have enough energy to penetrate a second aluminium plate when two thin layers were used instead of one thicker layer.
Unlike many traditional ultra-fast framing cameras the optical design of the SIM-8 provides the choice of up to eight 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 (>50lp/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.
