Image correlation for materials testing

Digital image correlation (DIC) is an established image processing method used in materials research to measure strain and displacement of samples under load at subpixel level. For example, a change in length due to integral strain can be measured as the difference in displacement between two image areas, comparable with a mechanical extensometer. In crack propagation experiments, crack path, crack length and crack flank displacement can be measured within the strain field to characterize the opening and closing behavior of the cracks that are forming.

Due to the high computational load, this process can be very slow when using conventional processors, which makes it impossible to adhere to the recommendations of relevant standards such as ASTM E606 regarding strain control or ASTM E647 on the evaluation of crack propagation tests.

GPU enables strain measurement with measurement rates of up to 1500 Hz

The solution is the use of graphics processing units (GPU) that make it possible to measure integral strain – like mechanical extensometers – at a rate of up to 1500 Hz, and to process up to 74,000 measuring points per second in real time in strain fields.

Fraunhofer IPM’s »real-time optical displacement measurement system« (RODiS) is the first optical strain measurement system to enable strain-controlled fatigue tests according to ASTM E606, as well as fast, contactless and marker-free crack propagation compliance measurements pursuant to ASTM E647 for metallic samples at temperatures of up to 1000 °C. In this context, »marker-free« means that the sample does not have to be treated with a marker (such as speckle varnish); instead, the untreated microstructure can be used as correlation pattern.

© Fraunhofer IPM
Stress-strain diagrams at 800 °C, marker-free (black curve) and with speckle varnish (red curve, right hand side images)
© Fraunhofer IPM
Strain control for uniaxial and biaxial samples according to ASTM E606 with up to 1500 Hz
© Fraunhofer IPM
Crack length measurement in uniaxial and biaxial samples according to ASTM E647
© Fraunhofer IPM
Simultaneous measurement of integral strain along the test stand axes (green) and of the strain and displacement field (color scale)

Applications »Digital image correlation«

 

Deformation measurement (2D & 3D)

Jahr
Year
Titel/Autor:in
Title/Author
Publikationstyp
Publication Type
2022 Direction- and path-independent DIC strain-field evaluation for uniaxial and biaxial fatigue crack growth investigations
Conrad, Fabian; Blug, Andreas; Regina, David Joel; Kerl, Julian; Bertz, Alexander; Kontermann, Christian; Oechsner, Matthias
Konferenzbeitrag
Conference Paper
2021 Combining GPU-based full-field and strain-controlled 2D-DIC for simplified crack growth experiments
Blug, Andreas; Conrad, Fabian; Regina, David Joel; Bertz, Alexander; Kontermann, Christian; Carl, Daniel; Oechsner, Matthias
Vortrag
Presentation
2020 GPU-based digital image correlation system for uniaxial and biaxial crack growth investigations
Conrad, Fabian; Blug, Andreas; Kerl, Julian; Fehrenbach, Jonathan; Regina, David Joel; Bertz, Alexander; Kontermann, Christian; Carl, Daniel; Oechsner, Matthias
Zeitschriftenaufsatz
Journal Article
2019 GPU-based digital image correlation system for real-time strain-controlled fatigue and strain field measurement
Blug, Andreas; Regina, David Joel; Eckmann, Stefan; Senn, Melanie; Eberl, Chris; Bertz, Alexander; Carl, Daniel
Konferenzbeitrag
Conference Paper
2019 Real-Time GPU-Based Digital Image Correlation Sensor for Marker-Free Strain-Controlled Fatigue Testing
Blug, Andreas; Regina, David Joel; Eckmann, Stefan; Senn, Melanie; Bertz, Alexander; Carl, Daniel; Eberl, Chris
Zeitschriftenaufsatz
Journal Article
2017 Marker-free GPU-based digital image correlation system for high-temperature strain-controlled fatigue measurements
Blug, Andreas; Regina, David Joel; Eckmann, Stefan; Senn, M.; Eberl, Christoph; Bertz, Alexander; Carl, Daniel
Vortrag
Presentation
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