2D Digital Image Correlation Applications

Vic 2D Applications         

In order for a setup to be a good 2D application (with just one camera), the specimen must be:

• Specimen must be flat
• Specimen must be planar to camera sensor
• No part of the specimen can have any out-of-plane motion towards or away from the camera

Since 2D is only working with one camera, the software must assume that the specimen in the image moves only in-plane and is completely flat and planar within that image.  If the test does not fall within these guidelines, then erroneous strains will be produced.  For example, in a tensile test, if the specimen necks and a region moves away from the camera, there will be a compression bias. Any motion away from the sensor will be reported as a compressive strain.  Any motion towards the sensor will be reported as a tensile strain.

Tips for 2D applications:

• Using a longer focal length will minimize bias due to out-of-plane motion.  The false strain produced by out of plane motion is equal to the amount of out-of-plane motion divided by the standoff distances between the lens and the specimen.
• 2D does not involve a calibration (other than a simple scale calibration), so low distortion lenses are preferred.  Since 2D is not calibrated the same way that 3D is, viewing through windows and mediums are more problematic in 2D.  Although, there is an inverse mapping method in 2D to remove these distortions.  This method involves translation stages, a high quality and flat speckle pattern that is larger than the field of view.  Procedurally, it is not as simple as standard 2d applications and sometimes not even logistically possible.