Detecting micro-displacement phenomenon in viscoelastic materials using 3D digital image correlation

One of the most interesting things about working with digital image correlation is that sometimes unexpected phenomena emerge when you least expect it.

This video, outlining a recent test conducted at a local shooting range, demonstrates persuasively the potential of the VIC-3D 10 DIC system for identifying micro-displacements in viscoelastic materials. While analyzing the data generated when a 9mm round was fired into a 6x6x16 block of ballistic gelatin, Correlated Solutions engineers noticed a clear wave propagating through the gel. What was unusual in this case was that the wave PRECEDED the impact of the bullet.

Our initial speculation, based on the lack of a similar wave when different bullets were tested, is that in a lucky coincidence of target distance, bullet speed, and the extremely precise measurement capability of VIC-3D 10, we were able to capture a displacement phenomenon caused by the pressure wave which emerged from the initial firing of the pistol and isolate it from the impact of the bullet. Have a look at the video and let us know what you think!

Here are a few more details.

The test utilized a conventional stereo DIC setup. After a speckle pattern was applied to the gel and the table was secured, the system was calibrated using a 28mm Correlated Solutions laser-marked calibration target. A pair of Photron Fastcam Nova S16s – equipped with 80-200 F2.8 lenses – were focused and set to trigger in the VIC-Snap software using an external trigger switch. When the appropriate safety procedures were in place, a MAGTECH FMJ, 115g, 9mm round was fired at 1250 ft/s into the gel from approximately 15 feet. The cameras were center-triggered at the sound of the shot, and they both captured images - 768 x 496 pixels in size - at 30,000 frames per second. In total, the cameras captured and stored more than 330,000 image pairs during the test of which 3000 pairs were saved and used for the DIC analysis in VIC-3D 10.

We are confident that this level of precision measurement will be valuable to engineers working with a wide range of cutting-edge materials. To find out more about this test or to explore how industry leading optical measurement systems from Correlated Solutions can impact your research, contact one of our sales engineers today.