Can Digital Image Correlation Replace Extensometers?

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Measuring Strain in Materials Testing

Materials testing is critical to input simulation models with the correct information. Engineers have been using physical extensometers, like clip gauges, for decades. They provide a measure of the strain between two points. This strain is then used for materials characterization (stress-strain curve, Poisson's ration, etc.). In the 90s and the 2000s, non-contact extensometers were first developed, like laser extensometers or video extensometers. These systems allow measurements that were not possible before, such as at high temperature or on thin materials. But these systems are typically less sensitive than traditional extensometers (sensitive to out of plane motion, producing fake readings of strain). Also, they are still limited to a 2-point measurement (4 points are possible on some models).

ARAMIS was developed as a non-contact alternative to physical sensors like strain gauges or extensometers. Based on 3D Digital Image Correlation (DIC), ARAMIS optically tracks features in 3D on the surface of components. It is, therefore, possible to track 2 or 4 points to match the capability of traditional, laser or video extensometers. But ARAMIS offers much more than that. By measuring the dynamic shape, displacement and strain maps of the coupon, it is possible to get much more out of a simple tensile test, like necking behaviors, Lüders bands, local delamination, negative effects of coupon clamping, and more.


Benefits of ARAMIS as an Alternative to Extensometers

  • It matches the precision of any extensometers, but non-contact and automated
  • It provides local strain measurements, even at high strain in the necking area
  • It automatically calculates materials properties according to ASTM and ISO standards
  • It can characterize local strain concentrations (Lüders bands, load fronts, local delamination...)
  • It can help understand the effects of coupon clamping (misalignment of clamps, bending, twisting...)

How to Implement ARAMIS in a Materials Laboratory?

The ARAMIS system can be mounted on a load frame, much like a laser or video extensometer. The ARAMIS Professional software controls the cameras seamlessly and outputs a full 3D mesh of the tested coupon, with options to display the dynamic shape, displacements, and axial or principal strain maps. The automated materials scripts and templates can then be used to quickly calculate all material properties according to common ASTM and ISO standards.

The ARAMIS Kiosk Mode is a simplified interface for test machines operators to easily collect and analyze the data according to common standards with a 4-step process (sample preparation, data acquisition, automated analysis, reporting). This automated process reduces test lead time and operator variability while producing unmatched data quality.

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