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Optical Measurement Methods

Digital Image Correlation

versatility, robustness, and ease of use

Digital Image Correlation (often referred to as “DIC”) is an easy-to-use optical method to measure deformation on an object’s surface. Digital Image Correlation has been proven over and over to be accurate when compared to valid FEA models. The DIC systems from Correlated Solutions utilize this advanced optical measurement technology.

Measurement Principle

DIC measures the shape (3D only), motion/displacement and deformation of objects by tracking natural or artificial prepared speckle patterns visible on their surface. This is done in small regions, called subsets. Here a subset is highlighted in red for camera image section covering 23 x 23 pixels. The pixels are represented by the grey value squares (e. g. digitized with 8 bit resolution), of which one is selected and marked in the subset and images in green. The subsets are numerically represented by the pixel grey values and their distribution.

Correlation principle: The subsets change their positions and shapes relative to the reference state. The VIC software models this displacement transformation (subset shape function) to define the deformed subset and displacement for its center (red cross) with subpixel resolution (e. g. 0,01 px).

Stereo triangulation principle

The principle of 2D correlation is now combined with the principle of stereo triangulation using two cameras (images). The positions of the subset centers (point P) prepared on the object surface are determined by the intersection of the corresponding light rays in VIC-3D. This allows to determine the shape (x, y, z) of the object surface from each image pair captured simultaneously for each deformation state.
As mentioned above, 3D deformations (U, V, W) is analysed relative to a reference state, but now between two stereo image pairs for each state. When combined with shape information, surface strains can be derived from the tangential (inplane) deformation fraction of a local number of points P and their deformation P(U, V, W) values, in combination with user defined spatial and timed filters in VIC-3D. The lack of contour information is one of the main limitations and sources of error for 2D DIC.

VIC-2D and VIC-3D stereo systems

What is required for a measurement?

The optoelectronic components include camera(s) with lenses, optional filters, and LED-based light source(s). Monochrome, low-noise, high-resolution, and high-speed cameras are available to suit different applications. The LED illumination minimizes thermal impact on the specimen and improves optical performance.
The mounting system includes a tripod with a 3D head, center column, and horizontal extension arm for precise positioning. For 3D DIC, it also features an adjustable stereo beam, fine camera alignment, and an optional linear stage for working distance and focus adjustment.
A desktop PC or laptop with the installed VIC software and hardware drivers is used to operate the system. Optional remote operation is available via the VIC-Snap app for smartphones and tablets.
The trigger and data acquisition unit synchronizes image acquisition with external analog signals e.g. force, displacement, or acceleration. It also triggers the cameras and light sources for stroboscopic illumination.
Accessories include tools for speckle pattern generation, such as rollers, stamps, printers, stickers, and airbrush equipment. For 3D DIC systems, calibration and certification equipment, including the optional VIC Gimbal, is also available.

Products

Explore our range of Digital Image Correlation (DIC) systems designed for precise, non-contact measurement and analysis.

Applications

Discover how our solutions are used across various industries to analyze deformation, strain, and material behavior.