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Real-Time GPU-Based Digital Image Correlation Sensor for Marker-Free Strain-Controlled Fatigue Testing

1
Fraunhofer Institute for Physical Measurement Techniques IPM, 79110 Freiburg, Germany
2
Fraunhofer Institute for Mechanics of Materials IWM, 79108 Freiburg, Germany
*
Author to whom correspondence should be addressed.
Appl. Sci. 2019, 9(10), 2025; https://doi.org/10.3390/app9102025
Received: 18 March 2019 / Revised: 7 May 2019 / Accepted: 10 May 2019 / Published: 16 May 2019
(This article belongs to the Special Issue High-speed Optical 3D Shape and Deformation Measurement)
PDF [2208 KB, uploaded 16 May 2019]

Abstract

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.
Keywords: digital image correlation; experimental mechanics; real-time image processing; closed-loop control; high-speed deformation measurement; general-purpose computing on graphics processing units (GPGPU) digital image correlation; experimental mechanics; real-time image processing; closed-loop control; high-speed deformation measurement; general-purpose computing on graphics processing units (GPGPU)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Blug, A.; Regina, D.J.; Eckmann, S.; Senn, M.; Bertz, A.; Carl, D.; Eberl, C. Real-Time GPU-Based Digital Image Correlation Sensor for Marker-Free Strain-Controlled Fatigue Testing. Appl. Sci. 2019, 9, 2025.

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