A Plexiglas panel was being evaluated during the course of a projectile impact. In addition to the obvious need for high speed, it was necessary to measure very large strains and displacements without interfering with the impact event.
Challenges
The Plexiglas panel underwent large and rapid displacements during the impact event. This made it very difficult to obtain accurate measurements. Any sensor in contact with the panel would undergo violent accelerations, which could damage the sensor and would certainly affect the movement of the panel. It was also desirable to measure strains at the leading edges of rapidly growing cracks. The exact location of the cracks was impossible to predict, and conventional methods could not provide such measurements even if the crack path had been predictable.
Solution
Correlated Solutions provided a high speed Vic-3D 2009 system for monitoring the panel. Images were captured at a rate of 10,000 frames per second. These images were then automatically processed to provide strain and displacement data for the entire surface of the panel. The displacement data clearly showed the peak values as well as primary and higher-order oscillations of the panel subsequent to the impact. It was also possible to measure strains during crack propagation and permanent deformations resulting from the impact.
Notice in the strain plots to the right that the peaks in the shear strain in the panel during impact form a star-like pattern. Upon visual investigation it was determined that the peak strain locations corresponded with the locations of crack formations in the panel. This gave researchers a valuable insight into the crack formation process caused by high-speed impact and allowed for important revisions to their analytical model of the event.
Links
Click here to go to the Vic-3D 2009 product page for more information about this technology.