Image correlation

Principle of 2D Digital Image Correlation

The digital image correlation is a camera based technique for the measurement of deformations on object surfaces. The method tracks the grey pattern (speckle pattern") in small neighborhoods (subset or facette shown light blue in below camera images.

DIC_theory
Reference state Deformed state

Fullfield measurement

The analysis of images and sequences with digital image correlation allows the measurement of displacements and deformations at every camera pixel. The resulting fullfield information is very comprehensive and has many advantages compared to other measurement techniques.
Below images shows the speckle pattern of an object before and after deformation and the measured strain distribution.
 
2d_dic_000
Reference state
2d_dic_014
Deformed state
2d_dic_e1_014
Strain distribution
 

 

2d_dic_e1_014

Measured strain field E1 from images sequence.
 
 
 

3D-DIC

During the object deformation stereo images are recorded with two cameras. The stereo correlation between the left and right images allows the measurement of the geometry and position of the object for every load stage.
The temporal correlation calculates the 3D displacement and 3D deformation of the object. Below speckle images are recorded simultaneously with the left and right camera of a stereo system.
 
stereocorrelation
3D-geometry through stereo correlation.


The temporal correlation of e.g. the left images of a sequence measures the displacements and deformations related to the reference state of the specimen.

3dstrain
Strain calculation through stereo correlation and temporal correlation.

 

Further application samples related to DIC are listed in the section Applications/digital images correlation.