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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

Fulltext ()

Applied Sciences 9 (2019), No.10, Art. 2025, 15 pp.
ISSN: 2076-3417
Journal Article, Electronic Publication
Fraunhofer IPM ()
Fraunhofer IWM ()
digital image correlation; real-time image processing; closed-loop control; High-Speed Deformation Measurement; GPGPU

Digital image correlation (DIC) is a highly accurate image-based deformation measurement method achieving a repeatability in the range of σ= 10−5 relative to the field-of-view. The method is well accepted in material testing for non-contact strain measurement. However, the correlation makes it computationally slow on conventional, CPU-based computers. Recently, there have been DIC implementations based on graphics processing units (GPU) for strain-field evaluations with numerous templates per image at rather low image rates, but there are no real-time implementations for fast strain measurements with sampling rates above 1 kHz. In this article, a GPU-based 2D-DIC system is described achieving a strain sampling rate of 1.2 kHz with a latency of less than 2 milliseconds. In addition, the system uses the incidental, characteristic microstructure of the specimen surface for marker-free correlation, without need for any surface preparation—even on polished hourglass specimen. The system generates an elongation signal for standard PID-controllers of testing machines so that it directly replaces mechanical extensometers. Strain-controlled LCF measurements of steel, aluminum, and nickel-based superalloys at temperatures of up to 1000 °C are reported and the performance is compared to other path-dependent and path-independent DIC systems. According to our knowledge, this is one of the first GPU-based image processing systems for real-time closed-loop applications.