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Institute of Turbomachinery and Fluid Dynamics
Logo Leibniz Universität Hannover
Institute of Turbomachinery and Fluid Dynamics
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Digital Image Correlation (DIC)

Field of Application

  • Non-contacting measurement of surface deformations for rotating machinery
  • Monitoring of rotor blade deformations for wind turbines
  • Stress analysis and modal analysis for individual machinery components

Measured Quantities

  • Deformation
  • Elongation
  • Tension
  • Damping
  • Frequency (FFT)

Description

Digital Image Correlation (DIC) is a non-invasive, optical measurement technique that can track surface motion and deformation over time. The relative surface motion over time is determined based on a set of reference images.

DIC can provide measurements of elongation and surface tension even for rotating machinery by removing rigid body motion. When combined with high speed image sensors DIC offers vast potential for vibration analysis on stationary and rotating machinery. 

A basic requirement for the application of DIC is a random, high-contrast and non-reflecting surface texture. If the natural texture of object does not fulfill this requirement an artificial texture can be applied. Different techniques for applying these textures include self-adhesive foil with a printed random pattern, a pattern directly printed on the surface or even toner sprinkled on the surface of the object.

The first step of the image analysis subdivides the random pattern of the surface of the reference image into discrete subsets. These exact subsets are later recovered in every image of the test series by means of a correlation algorithm. The result is a vector field for each image that represents the motion of the subsets relative to the reference image.  Application of sub-pixel interpolation enables the correlation algorithm to detect movements as little as 0.01 pixels.

Digital Image Correlation can be applied with a single camera setup for 2D planar motion. For 3D motion at least two cameras are needed in a stereoscopic setup. The line of sight for a single camera setup must be perpendicular to the surface of interest and only motions perpendicular to the camera can be recovered. A stereoscopic setup with at least two cameras is not limited by these restrictions. With two cameras 3D motions of arbitrary surfaces can be recovered. Additionally the line of sight for a stereoscopic setup is not restricted. For many applications even acute viewing angles onto the surface of the object are possible.

Contact

Stephanie Lehnhoff, M.Eng.