3D Digital Image Correlation (DIC) is an optical Computer Aided Engineering (CAE) method that makes use stereoscopic technology to track displacements and strains of a target surface over time. The surface is tracked by using a random surface pattern (commonly referred to as “speckling”).
Applying DIC to blast testing of armour
An explosion is a blindingly fast event. The role of the armour is to protect people’s lives, and it does so by shielding them from the blast and absorbing part of its energy. The armour undergoes both elastic and plastic deformation. The full event is over in about 1/10th of the time that it would take you to blink, and by that time the residual shape of the armour bears no resemblance to the peak dynamic deformation that it had undergone just a few milliseconds earlier. In armour design, it is of paramount importance to measure this peak dynamic deformation. If the armour deforms too much, it might for example injure or kill the occupants of a vehicle. Test houses typically rely on shorting pins or honeycombs to gain an understanding of maximum dynamic deflection. These measurement methods have severe limitations, as they provide limited information and can get destroyed in the loadcase.
Advantages of 3D DIC
3D DIC provides a number of unique advantages;
1. As a non-contact optical technique, there is no need for any physical instrumentation to be attached to the armour.
2. Data is captured for the entire surface, as opposed to physical techniques (i.e. shorting pins) which only measure displacements in a particular area. DIC extracts data from the whole visible surface and not only how much it deforms, but also how it deforms.
3. A wealth of information. DIC extracts 3D information on displacements, strains, velocities and accelerations.
A CAE Analyst’s dream
The ultimate value of DIC and where it stands head and shoulders over traditional techniques is when used in conjunction with Computer Aided Engineering. By allowing the user to generate time-dependent contour plots, DIC bridges the gap between Finite Element Analysis (FEA) and experimental testing and is the ultimate correlation tool for CAE model correlation.